From: Bruce Momjian Date: Sat, 9 Dec 2000 04:29:38 +0000 (+0000) Subject: Update FAQ. X-Git-Tag: REL7_1_BETA2~219 X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=5eced96f2c2d038026ce29b41b38ed428e96c437;p=postgresql Update FAQ. --- diff --git a/doc/FAQ b/doc/FAQ index 11a4783ab8..69f40498fa 100644 --- a/doc/FAQ +++ b/doc/FAQ @@ -214,31 +214,29 @@ available for discussion of matters pertaining to PostgreSQL. To subscribe, send mail with the following lines in the body (not the subject line) - subscribe - end + subscribe + end to pgsql-general-request@PostgreSQL.org. There is also a digest list available. To subscribe to this list, send email to: pgsql-general-digest-request@PostgreSQL.org with a body of: - subscribe - end + subscribe + end Digests are sent out to members of this list whenever the main list has received around 30k of messages. The bugs mailing list is available. To subscribe to this list, send email to pgsql-bugs-request@PostgreSQL.org with a body of: - - subscribe - end + subscribe + end There is also a developers discussion mailing list available. To subscribe to this list, send email to pgsql-hackers-request@PostgreSQL.org with a body of: - - subscribe - end + subscribe + end Additional mailing lists and information about PostgreSQL can be found via the PostgreSQL WWW home page at: @@ -284,7 +282,7 @@ http://ourworld.compuserve.com/homepages/graeme_birchall/HTM_COOK.HTM. Another one is "Teach Yourself SQL in 21 Days, Second Edition" at - http://members.tripod.com/er4ebus/sql/index.htm + http://members.tripod.com/er4ebus/sql/index.htm Many of our users like The Practical SQL Handbook, Bowman, Judith S., et al., Addison-Wesley. Others like The Complete Reference SQL, Groff @@ -558,8 +556,8 @@ Both postmaster and postgres have several debug options available. First, whenever you start the postmaster, make sure you send the standard output and error to a log file, like: - cd /usr/local/pgsql - ./bin/postmaster >server.log 2>&1 & + cd /usr/local/pgsql + ./bin/postmaster >server.log 2>&1 & This will put a server.log file in the top-level PostgreSQL directory. This file contains useful information about problems or errors @@ -668,11 +666,11 @@ 4.5) How do you remove a column from a table? We do not support ALTER TABLE DROP COLUMN, but do this: - SELECT ... -- select all columns but the one you want to remove - INTO TABLE new_table - FROM old_table; - DROP TABLE old_table; - ALTER TABLE new_table RENAME TO old_table; + SELECT ... -- select all columns but the one you want to remove + INTO TABLE new_table + FROM old_table; + DROP TABLE old_table; + ALTER TABLE new_table RENAME TO old_table; 4.6) What is the maximum size for a row, table, database? @@ -680,7 +678,7 @@ Maximum size for a database? unlimited (60GB databases exist) Maximum size for a table? unlimited on all operating systems Maximum size for a row? 8k, configurable to 32k -Maximum number of rows in a table? unlimited +Maximum number of rows in a table? unlimited Maximum number of columns in a table? unlimited Maximum number of indexes on a table? unlimited @@ -798,7 +796,7 @@ Maximum number of indexes on a table? unlimited case-insensitive regular expression matching. There is no case-insensitive variant of the LIKE operator, but you can get the effect of case-insensitive LIKE with this: - WHERE lower(textfield) LIKE lower(pattern) + WHERE lower(textfield) LIKE lower(pattern) 4.14) In a query, how do I detect if a field is NULL? @@ -818,8 +816,8 @@ BYTEA bytea variable-length byte array (null-safe) some error messages. The last four types above are "varlena" types (i.e., the first four - bytes on disk are the length, followed by the data). Thus the actual - space used is slightly greater than the declared size. However, these + bytes on disk are the length, followed by the data). Thus the actual + space used is slightly greater than the declared size. However, these data types are also subject to compression or being stored out-of-line by TOAST, so the space on disk might also be less than expected. @@ -827,18 +825,18 @@ BYTEA bytea variable-length byte array (null-safe) PostgreSQL supports a SERIAL data type. It auto-creates a sequence and index on the column. For example, this: - CREATE TABLE person ( - id SERIAL, - name TEXT - ); + CREATE TABLE person ( + id SERIAL, + name TEXT + ); is automatically translated into this: - CREATE SEQUENCE person_id_seq; - CREATE TABLE person ( - id INT4 NOT NULL DEFAULT nextval('person_id_seq'), - name TEXT - ); - CREATE UNIQUE INDEX person_id_key ON person ( id ); + CREATE SEQUENCE person_id_seq; + CREATE TABLE person ( + id INT4 NOT NULL DEFAULT nextval('person_id_seq'), + name TEXT + ); + CREATE UNIQUE INDEX person_id_key ON person ( id ); See the create_sequence manual page for more information about sequences. You can also use each row's OID field as a unique value. @@ -853,8 +851,8 @@ BYTEA bytea variable-length byte array (null-safe) object with the nextval() function before inserting and then insert it explicitly. Using the example table in 4.16.1, that might look like this: - $newSerialID = nextval('person_id_seq'); - INSERT INTO person (id, name) VALUES ($newSerialID, 'Blaise Pascal'); + $newSerialID = nextval('person_id_seq'); + INSERT INTO person (id, name) VALUES ($newSerialID, 'Blaise Pascal'); You would then also have the new value stored in $newSerialID for use in other queries (e.g., as a foreign key to the person table). Note @@ -864,8 +862,8 @@ BYTEA bytea variable-length byte array (null-safe) Alternatively, you could retrieve the assigned SERIAL value with the currval() function after it was inserted by default, e.g., - INSERT INTO person (name) VALUES ('Blaise Pascal'); - $newID = currval('person_id_seq'); + INSERT INTO person (name) VALUES ('Blaise Pascal'); + $newID = currval('person_id_seq'); Finally, you could use the OID returned from the INSERT statement to look up the default value, though this is probably the least portable @@ -933,8 +931,8 @@ BYTEA bytea variable-length byte array (null-safe) It is possible you have run out of virtual memory on your system, or your kernel has a low limit for certain resources. Try this before starting the postmaster: - ulimit -d 65536 - limit datasize 64m + ulimit -d 65536 + limit datasize 64m Depending on your shell, only one of these may succeed, but it will set your process data segment limit much higher and perhaps allow the @@ -964,21 +962,21 @@ BYTEA bytea variable-length byte array (null-safe) 4.22) How do I create a column that will default to the current time? Use now(): - CREATE TABLE test (x int, modtime timestamp DEFAULT now() ); +CREATE TABLE test (x int, modtime timestamp DEFAULT now() ); 4.23) Why are my subqueries using IN so slow? Currently, we join subqueries to outer queries by sequentially scanning the result of the subquery for each row of the outer query. A workaround is to replace IN with EXISTS: - SELECT * - FROM tab - WHERE col1 IN (SELECT col2 FROM TAB2) +SELECT * + FROM tab + WHERE col1 IN (SELECT col2 FROM TAB2) to: - SELECT * - FROM tab - WHERE EXISTS (SELECT col2 FROM TAB2 WHERE col1 = col2) +SELECT * + FROM tab + WHERE EXISTS (SELECT col2 FROM TAB2 WHERE col1 = col2) We hope to fix this limitation in a future release. @@ -988,14 +986,14 @@ BYTEA bytea variable-length byte array (null-safe) can be simulated using UNION and NOT IN. For example, when joining tab1 and tab2, the following query does an outer join of the two tables: - SELECT tab1.col1, tab2.col2 - FROM tab1, tab2 - WHERE tab1.col1 = tab2.col1 - UNION ALL - SELECT tab1.col1, NULL - FROM tab1 - WHERE tab1.col1 NOT IN (SELECT tab2.col1 FROM tab2) - ORDER BY tab1.col1 + SELECT tab1.col1, tab2.col2 + FROM tab1, tab2 + WHERE tab1.col1 = tab2.col1 + UNION ALL + SELECT tab1.col1, NULL + FROM tab1 + WHERE tab1.col1 NOT IN (SELECT tab2.col1 FROM tab2) + ORDER BY tab1.col1 _________________________________________________________________ Extending PostgreSQL diff --git a/doc/src/FAQ/FAQ.html b/doc/src/FAQ/FAQ.html index 1123086be9..fd655a9ead 100644 --- a/doc/src/FAQ/FAQ.html +++ b/doc/src/FAQ/FAQ.html @@ -1,877 +1,917 @@ - - -PostgreSQL FAQ - - -

-Frequently Asked Questions (FAQ) for PostgreSQL -

-

-Last updated: Tue Oct 17 00:21:20 EDT 2000 -

-Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)

- -The most recent version of this document can be viewed at - -http://www.PostgreSQL.org/docs/faq-english.html.

- -Platform-specific questions are answered at http://www.PostgreSQL.org/docs/.

- -

- -

General Questions

- -1.1) What is PostgreSQL?
-1.2) What's the copyright on PostgreSQL?
-1.3) What Unix platforms does PostgreSQL run on?
-1.4) What non-unix ports are available?
-1.5) Where can I get PostgreSQL?
-1.6) Where can I get support?
-1.7) What is the latest release?
-1.8) What documentation is available?
-1.9) How do I find out about known bugs or missing features?
-1.10) How can I learn SQL?
-1.11) Is PostgreSQL Y2K compliant?
-1.12) How do I join the development team?
-1.13) How do I submit a bug report?
-1.14) How does PostgreSQL compare to other DBMS's?
- - -

User Client Questions

- -2.1) Are there ODBC drivers for -PostgreSQL?
-2.2) What tools are available for hooking -PostgreSQL to Web pages?
-2.3) Does PostgreSQL have a graphical user interface? -A report generator? An embedded query language interface?
-2.4) What languages are available to communicate -with PostgreSQL?
- - -

Administrative Questions

- -3.1) Why does initdb fail?
-3.2) How do I install PostgreSQL somewhere other than -/usr/local/pgsql?
-3.3) When I start the postmaster, I get a -Bad System Call or core dumped message. Why?
-3.4) When I try to start the postmaster, I get -IpcMemoryCreate errors. Why?
-3.5) When I try to start the postmaster, I get -IpcSemaphoreCreate errors. Why?
-3.6) How do I prevent other hosts from accessing my -PostgreSQL database?
-3.7) Why can't I connect to my database from -another machine?
-3.8) Why can't I access the database as the -root user?
-3.9) All my servers crash under concurrent -table access. Why?
-3.10) How do I tune the database engine for -better performance?
-3.11) What debugging features are available?
-3.12) I get "Sorry, too many clients" when trying to -connect. Why?
-3.13) What are the pg_sorttempNNN.NN files in my -database directory?
- -

Operational Questions

- -4.1) Why is the system confused about commas, -decimal points, and date formats.
-4.2) What is the exact difference between -binary cursors and normal cursors?
-4.3) How do I SELECT only the first few rows of -a query?
- -4.4) How do I get a list of tables or other -things I can see in psql?
-4.5) How do you remove a column from a table?
- -4.6) What is the maximum size for a -row, table, database?
-4.7) How much database disk space is required -to store data from a typical text file?
- -4.8) How do I find out what indices or -operations are defined in the database?
-4.9) My queries are slow or don't make use of the -indexes. Why?
-4.10) How do I see how the query optimizer is -evaluating my query?
-4.11) What is an R-tree index?
-4.12) What is Genetic Query Optimization?
- -4.13) How do I do regular expression searches -and case-insensitive regular expression searches?
-4.14) In a query, how do I detect if a field -is NULL?
-4.15) What is the difference between the -various character types?
-4.16.1) How do I create a serial/auto-incrementing field?
-4.16.2) How do I get the value of a -SERIAL insert?
-4.16.3) Don't currval() and nextval() lead to a -race condition with other users?
- -4.17) What is an OID? What is a -TID?
-4.18) What is the meaning of some of the terms -used in PostgreSQL?
- -4.19) Why do I get the error "FATAL: palloc -failure: memory exhausted?"
-4.20) How do I tell what PostgreSQL version I -am running?
-4.21) My large-object operations get invalid -large obj descriptor. Why?
-4.22) How do I create a column that will default to the -current time?
-4.23) Why are my subqueries using -IN so slow?
-4.24) How do I do an outer join?
- -

Extending PostgreSQL

- -5.1) I wrote a user-defined function. When I run -it in psql, why does it dump core?
-5.2) What does the message -"NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!" mean?
-5.3) How can I contribute some nifty new types and functions -to PostgreSQL?
-5.4) How do I write a C function to return a -tuple?
-5.5) I have changed a source file. Why does the -recompile not see the change?
- - -
- -

General Questions

-

1.1) What is PostgreSQL?

- -PostgreSQL is an enhancement of the POSTGRES database management system, -a next-generation DBMS research prototype. While PostgreSQL retains the -powerful data model and rich data types of POSTGRES, it replaces the -PostQuel query language with an extended subset of SQL. PostgreSQL is -free and the complete source is available.

- -PostgreSQL development is performed by a team of Internet -developers who all subscribe to the PostgreSQL development mailing list. -The current coordinator is Marc G. Fournier (scrappy@PostgreSQL.org). (See -below on how to join). This team is now responsible for all development -of PostgreSQL.

- -The authors of PostgreSQL 1.01 were Andrew Yu and Jolly Chen. Many -others have contributed to the porting, testing, debugging, and -enhancement of the code. The original Postgres code, from which -PostgreSQL is derived, was the effort of many graduate students, -undergraduate students, and staff programmers working under the -direction of Professor Michael Stonebraker at the University of -California, Berkeley.

- -The original name of the software at Berkeley was Postgres. When SQL -functionality was added in 1995, its name was changed to Postgres95. The -name was changed at the end of 1996 to PostgreSQL.

- -It is pronounced Post-Gres-Q-L. - -

1.2) What's the copyright on -PostgreSQL?

- -PostgreSQL is subject to the following COPYRIGHT:

- -PostgreSQL Data Base Management System

- -Portions copyright (c) 1996-2000, PostgreSQL, Inc - -Portions Copyright (c) 1994-6 Regents of the University of California

- -Permission to use, copy, modify, and distribute this software and its -documentation for any purpose, without fee, and without a written -agreement is hereby granted, provided that the above copyright notice -and this paragraph and the following two paragraphs appear in all -copies.

- -IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY -FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, -INCLUDING LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS -DOCUMENTATION, EVEN IF THE UNIVERSITY OF CALIFORNIA HAS BEEN ADVISED OF -THE POSSIBILITY OF SUCH DAMAGE.

- -THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES, -INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY -AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER -IS ON AN "AS IS" BASIS, AND THE UNIVERSITY OF CALIFORNIA HAS NO -OBLIGATIONS TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR -MODIFICATIONS.

- - - -

1.3) What Unix platforms does PostgreSQL run -on?

- -The authors have compiled and tested PostgreSQL on the following -platforms (some of these compiles require gcc): -

-

- -

1.4) What non-unix ports are available?

- -It is possible to compile the libpq C library, psql, and other -interfaces and binaries to run on MS Windows platforms. In this case, -the client is running on MS Windows, and communicates via TCP/IP to a -server running on one of our supported Unix platforms.

- -A file win31.mak is included in the distribution for making a -Win32 libpq library and psql.

- -The database server is now working on Windows NT using Cygwin, the -Cygnus Unix/NT porting library. See pgsql/doc/FAQ_NT in the -distribution. It does not work on MS Windows 9X because Cygwin does not -support the features we need on those platforms.

- - -

1.5) Where can I get PostgreSQL?

-The primary anonymous ftp site for PostgreSQL is -ftp://ftp.PostgreSQL.org/pub. -For mirror sites, see our main Web site. - -

1.6) Where can I get support?

- -There is no support for PostgreSQL from the University of -California, Berkeley. It is maintained through volunteer effort.

- -The main mailing list is: pgsql-general@PostgreSQL.org. -It is available for discussion of matters pertaining to PostgreSQL. -To subscribe, send mail with the following lines in the body (not -the subject line) - -

-	subscribe
-	end
-

- -to pgsql-general-request@PostgreSQL.org.

- -There is also a digest list available. To subscribe to this list, send -email to: -pgsql-general-digest-request@PostgreSQL.org with a body of: - -

-	subscribe
-	end
-
- -Digests are sent out to members of this list whenever the main list has -received around 30k of messages.

- -The bugs mailing list is available. To subscribe to this list, send email -to pgsql-bugs-request@PostgreSQL.org -with a body of:

- -

-	subscribe
-	end
-
- -There is also a developers discussion mailing list available. To -subscribe to this list, send email to pgsql-hackers-request@PostgreSQL.org -with a body of:

- -

-	subscribe
-	end
-

- -Additional mailing lists and information about PostgreSQL can be found -via the PostgreSQL WWW home page at: - -

-http://www.PostgreSQL.org -

- -There is also an IRC channel on EFNet, channel #PostgreSQL. -I use the unix command irc -c '#PostgreSQL' "$USER" -irc.phoenix.net.

- -Commercial support for PostgreSQL is available at http://www.pgsql.com/.

- - -

1.7) What is the latest release?

- -The latest release of PostgreSQL is version 7.0.2.

- -We plan to have major releases every four months.

- - -

1.8) What documentation is available?

- -Several manuals, manual pages, and some small test examples are -included in the distribution. See the /doc directory. You can also -browse the manual online at -http://www.PostgreSQL.org/docs/postgres. -

- -There is a PostgreSQL book available at -http://www.PostgreSQL.org/docs/awbook.html.

- -psql has some nice \d commands to show information about types, -operators, functions, aggregates, etc.

+ -Our Web site contains even more documentation.

- -

1.9) How do I find out about known bugs or missing features? -

- -PostgreSQL supports an extended subset of SQL-92. See our - -TODO list for known bugs, missing features, and future plans.

- -

1.10) How can I learn SQL?

- -The PostgreSQL book at -http://www.PostgreSQL.org/docs/awbook.html teaches SQL. - -There is a nice tutorial at -http://w3.one.net/~jhoffman/sqltut.htm and at -http://ourworld.compuserve.com/homepages/graeme_birchall/HTM_COOK.HTM.

+ + + + + PostgreSQL FAQ + + + +

Frequently Asked Questions (FAQ) for PostgreSQL

+ +

Last updated: Tue Oct 17 00:21:20 EDT 2000

+ +

Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
+

+ +

The most recent version of this document can be viewed at http://www.PostgreSQL.org/docs/faq-english.html.

+ +

Platform-specific questions are answered at http://www.PostgreSQL.org/docs/.

+
+ +
+

General Questions

+
+ 1.1) What is PostgreSQL?
+ 1.2) What's the copyright on PostgreSQL?
+ 1.3) What Unix platforms does PostgreSQL run + on?
+ 1.4) What non-unix ports are available?
+ 1.5) Where can I get PostgreSQL?
+ 1.6) Where can I get support?
+ 1.7) What is the latest release?
+ 1.8) What documentation is available?
+ 1.9) How do I find out about known bugs or + missing features?
+ 1.10) How can I learn SQL?
+ 1.11) Is PostgreSQL Y2K compliant?
+ 1.12) How do I join the development team?
+ 1.13) How do I submit a bug report?
+ 1.14) How does PostgreSQL compare to other + DBMS's?
+ + +
+

User Client Questions

+
+ 2.1) Are there ODBC drivers for PostgreSQL?
+ 2.2) What tools are available for hooking + PostgreSQL to Web pages?
+ 2.3) Does PostgreSQL have a graphical user + interface? A report generator? An embedded query language + interface?
+ 2.4) What languages are available to + communicate with PostgreSQL?
+ + +
+

Administrative Questions

+
+ 3.1) Why does initdb fail?
+ 3.2) How do I install PostgreSQL somewhere + other than /usr/local/pgsql?
+ 3.3) When I start the postmaster, I get + a Bad System Call or core dumped message. Why?
+ 3.4) When I try to start the postmaster, + I get IpcMemoryCreate errors. Why?
+ 3.5) When I try to start the postmaster, + I get IpcSemaphoreCreate errors. Why?
+ 3.6) How do I prevent other hosts from + accessing my PostgreSQL database?
+ 3.7) Why can't I connect to my database from + another machine?
+ 3.8) Why can't I access the database as the + root user?
+ 3.9) All my servers crash under concurrent + table access. Why?
+ 3.10) How do I tune the database engine for + better performance?
+ 3.11) What debugging features are + available?
+ 3.12) I get "Sorry, too many clients" + when trying to connect. Why?
+ 3.13) What are the pg_sorttempNNN.NN + files in my database directory?
+ + +
+

Operational Questions

+
+ 4.1) Why is the system confused about commas, + decimal points, and date formats.
+ 4.2) What is the exact difference between + binary cursors and normal cursors?
+ 4.3) How do I SELECT only the + first few rows of a query?
+ 4.4) How do I get a list of tables or other + things I can see in psql?
+ 4.5) How do you remove a column from a + table?
+ 4.6) What is the maximum size for a row, table, + database?
+ 4.7) How much database disk space is required + to store data from a typical text file?
+ 4.8) How do I find out what indices or + operations are defined in the database?
+ 4.9) My queries are slow or don't make use of + the indexes. Why?
+ 4.10) How do I see how the query optimizer is + evaluating my query?
+ 4.11) What is an R-tree index?
+ 4.12) What is Genetic Query Optimization?
+ 4.13) How do I do regular expression searches + and case-insensitive regular expression searches?
+ 4.14) In a query, how do I detect if a field + is NULL?
+ 4.15) What is the difference between the + various character types?
+ 4.16.1) How do I create a + serial/auto-incrementing field?
+ 4.16.2) How do I get the value of a + SERIAL insert?
+ 4.16.3) Don't currval() and + nextval() lead to a race condition with other users?
+ 4.17) What is an OID? What is a + TID?
+ 4.18) What is the meaning of some of the terms + used in PostgreSQL?
+ 4.19) Why do I get the error "FATAL: palloc + failure: memory exhausted?"
+ 4.20) How do I tell what PostgreSQL version I + am running?
+ 4.21) My large-object operations get + invalid large obj descriptor. Why?
+ 4.22) How do I create a column that will + default to the current time?
+ 4.23) Why are my subqueries using + IN so slow?
+ 4.24) How do I do an outer join?
+ + +
+

Extending PostgreSQL

+
+ 5.1) I wrote a user-defined function. When I run + it in psql, why does it dump core?
+ 5.2) What does the message + "NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!" + mean?
+ 5.3) How can I contribute some nifty new types + and functions to PostgreSQL?
+ 5.4) How do I write a C function to return a + tuple?
+ 5.5) I have changed a source file. Why does the + recompile not see the change?
+ +
+ +
+

General Questions

+
+ +

1.1) What is PostgreSQL?

+ +

PostgreSQL is an enhancement of the POSTGRES database management + system, a next-generation DBMS research prototype. While PostgreSQL + retains the powerful data model and rich data types of POSTGRES, it + replaces the PostQuel query language with an extended subset of + SQL. PostgreSQL is free and the complete source is available.

+ +

PostgreSQL development is performed by a team of Internet + developers who all subscribe to the PostgreSQL development mailing + list. The current coordinator is Marc G. Fournier (scrappy@PostgreSQL.org). (See + below on how to join). This team is now responsible for all + development of PostgreSQL.

+ +

The authors of PostgreSQL 1.01 were Andrew Yu and Jolly Chen. + Many others have contributed to the porting, testing, debugging, + and enhancement of the code. The original Postgres code, from which + PostgreSQL is derived, was the effort of many graduate students, + undergraduate students, and staff programmers working under the + direction of Professor Michael Stonebraker at the University of + California, Berkeley.

+ +

The original name of the software at Berkeley was Postgres. When + SQL functionality was added in 1995, its name was changed to + Postgres95. The name was changed at the end of 1996 to + PostgreSQL.

+ +

It is pronounced Post-Gres-Q-L.

+ +

1.2) What's the copyright on PostgreSQL?

+ +

PostgreSQL is subject to the following COPYRIGHT:

+ +

PostgreSQL Data Base Management System

+ +

Portions copyright (c) 1996-2000, PostgreSQL, Inc Portions + Copyright (c) 1994-6 Regents of the University of California

+ +

Permission to use, copy, modify, and distribute this software + and its documentation for any purpose, without fee, and without a + written agreement is hereby granted, provided that the above + copyright notice and this paragraph and the following two + paragraphs appear in all copies.

+ +

IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY + PARTY FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL + DAMAGES, INCLUDING LOST PROFITS, ARISING OUT OF THE USE OF THIS + SOFTWARE AND ITS DOCUMENTATION, EVEN IF THE UNIVERSITY OF + CALIFORNIA HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

+ +

THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY + WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES + OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE + SOFTWARE PROVIDED HEREUNDER IS ON AN "AS IS" BASIS, AND THE + UNIVERSITY OF CALIFORNIA HAS NO OBLIGATIONS TO PROVIDE MAINTENANCE, + SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.

+ +

1.3) What Unix platforms does PostgreSQL run + on?

+ +

The authors have compiled and tested PostgreSQL on the following + platforms (some of these compiles require gcc):

+ + -

1.14) How does PostgreSQL compare to other -DBMS's?

+

1.4) What non-unix ports are available?

-There are several ways of measuring software: features, performance, -reliability, support, and price.

+

It is possible to compile the libpq C library, psql, and + other interfaces and binaries to run on MS Windows platforms. In + this case, the client is running on MS Windows, and communicates + via TCP/IP to a server running on one of our supported Unix + platforms.

-
-
Features -
+

A file win31.mak is included in the distribution for + making a Win32 libpq library and psql.

-PostgreSQL has most features present in large commercial DBMS's, like -transactions, subselects, triggers, views, foreign key referential -integrity, and sophisticated locking. We have some features they don't -have, like user-defined types, inheritance, rules, and multi-version -concurrency control to reduce lock contention. We don't have outer -joins, but are working on them.

+

The database server is now working on Windows NT using Cygwin, + the Cygnus Unix/NT porting library. See pgsql/doc/FAQ_NT in + the distribution. It does not work on MS Windows 9X because Cygwin + does not support the features we need on those platforms.

-
Performance -
+

1.5) Where can I get PostgreSQL?

-PostgreSQL runs in two modes. Normal fsync mode flushes every -completed transaction to disk, guaranteeing that if the OS crashes or -loses power in the next few seconds, all your data is safely stored on -disk. In this mode, we are slower than most commercial databases, partly -because few of them do such conservative flushing to disk in their -default modes. In no-fsync mode, we are usually faster than -commercial databases, though in this mode, an OS crash could cause data -corruption. We are working to provide an intermediate mode that suffers -less performance overhead than full fsync mode, and will allow data -integrity within 30 seconds of an OS crash.

+

The primary anonymous ftp site for PostgreSQL is ftp://ftp.PostgreSQL.org/pub. + For mirror sites, see our main Web site.

-In comparison to MySQL or leaner database systems, we are slower on -inserts/updates because we have transaction overhead. Of course, MySQL -doesn't have any of the features mentioned in the Features -section above. We are built for flexibility and features, though we -continue to improve performance through profiling and source code -analysis. There is an interesting Web page comparing PostgreSQL to MySQL -at -http://openacs.org/why-not-mysql.html

+

1.6) Where can I get support?

-We handle each user connection by creating a Unix process. Backend -processes share data buffers and locking information. With multiple -CPU's, multiple backends can easily run on different CPU's.

+

There is no support for PostgreSQL from the University of + California, Berkeley. It is maintained through volunteer + effort.

-
Reliability -
+

The main mailing list is: pgsql-general@PostgreSQL.org. + It is available for discussion of matters pertaining to PostgreSQL. + To subscribe, send mail with the following lines in the body (not + the subject line)

+
+    subscribe
+    end
+
-We realize that a DBMS must be reliable, or it is worthless. We strive -to release well-tested, stable code that has a minimum of bugs. Each -release has at least one month of beta testing, and our release history -shows that we can provide stable, solid releases that are ready for -production use. We believe we compare favorably to other database -software in this area.

+

to pgsql-general-request@PostgreSQL.org.

-
Support -
+

There is also a digest list available. To subscribe to this + list, send email to: pgsql-general-digest-request@PostgreSQL.org + with a body of:

+
+    subscribe
+    end
+
+ Digests are sent out to members of this list whenever the main list + has received around 30k of messages. -Our mailing list provides a large group of developers and users to help -resolve any problems encountered. While we can not guarantee a fix, -commercial DBMS's don't always supply a fix either. Direct access to -developers, the user community, manuals, and the source code often make -PostgreSQL support superior to other DBMS's. -There is commercial per-incident support available for those who need -it. (See support FAQ item.)

+

The bugs mailing list is available. To subscribe to this list, + send email to pgsql-bugs-request@PostgreSQL.org + with a body of:

+
+    subscribe
+    end
+
+ There is also a developers discussion mailing list available. To + subscribe to this list, send email to pgsql-hackers-request@PostgreSQL.org + with a body of: +
+    subscribe
+    end
+
-
Price -
+

Additional mailing lists and information about PostgreSQL can be + found via the PostgreSQL WWW home page at:

-We are free for all use, both commercial and non-commercial. You can -add our code to your product with no limitations, except those outlined -in our BSD-style license stated above.

-
+
+ http://www.PostgreSQL.org +
-
+

There is also an IRC channel on EFNet, channel + #PostgreSQL. I use the unix command irc -c + '#PostgreSQL' "$USER" irc.phoenix.net.

-

User Client Questions

-

+

Commercial support for PostgreSQL is available at http://www.pgsql.com/.

+

1.7) What is the latest release?

+

The latest release of PostgreSQL is version 7.0.2.

-

2.1) Are there ODBC drivers for PostgreSQL?

+

We plan to have major releases every four months.

-There are two ODBC drivers available, PsqlODBC and OpenLink ODBC.

+

1.8) What documentation is available?

-PsqlODBC is included in the distribution. More information about it can -be gotten from -ftp://ftp.PostgreSQL.org/pub/odbc/.

+

Several manuals, manual pages, and some small test examples are + included in the distribution. See the /doc directory. You + can also browse the manual online at http://www.PostgreSQL.org/docs/postgres.

-OpenLink ODBC can be gotten from -http://www.openlinksw.com. It works with their standard ODBC client -software so you'll have PostgreSQL ODBC available on every client -platform they support (Win, Mac, Unix, VMS).

+

There is a PostgreSQL book available at http://www.PostgreSQL.org/docs/awbook.html.

-They will probably be selling this product to people who need -commercial-quality support, but a freeware version will always be -available. Questions to postgres95@openlink.co.uk.

+

psql has some nice \d commands to show information about + types, operators, functions, aggregates, etc.

-See also the -ODBC chapter of the Programmer's Guide.

+

Our Web site contains even more documentation.

+ +

1.9) How do I find out about known bugs or + missing features?

+ +

PostgreSQL supports an extended subset of SQL-92. See our TODO list for + known bugs, missing features, and future plans.

+

1.10) How can I learn SQL?

+ +

The PostgreSQL book at http://www.PostgreSQL.org/docs/awbook.html + teaches SQL. There is a nice tutorial at http://w3.one.net/~jhoffman/sqltut.htm + and at + http://ourworld.compuserve.com/homepages/graeme_birchall/HTM_COOK.HTM.

+ +

Another one is "Teach Yourself SQL in 21 Days, Second Edition" + at http://members.tripod.com/er4ebus/sql/index.htm

+ +

Many of our users like The Practical SQL Handbook, + Bowman, Judith S., et al., Addison-Wesley. Others like The + Complete Reference SQL, Groff et al., McGraw-Hill.

+ +

1.11) Is PostgreSQL Y2K compliant?

+ +

Yes, we easily handle dates past the year 2000AD, and before + 2000BC.

+ +

1.12) How do I join the development + team?

+ +

First, download the latest source and read the PostgreSQL + Developers documentation on our Web site, or in the distribution. + Second, subscribe to the pgsql-hackers and + pgsql-patches mailing lists. Third, submit high-quality + patches to pgsql-patches.

+ +

There are about a dozen people who have commit privileges to the + PostgreSQL CVS archive. They each have submitted so many + high-quality patches that it was impossible for the existing + committers to keep up, and we had confidence that patches they + committed were of high quality.

+ +

1.13) How do I submit a bug report?

+ +

Fill out the "bug-template" file and send it to: pgsql-bugs@PostgreSQL.org

+ +

Also check out our ftp site ftp://ftp.PostgreSQL.org/pub to + see if there is a more recent PostgreSQL version or patches.

+ +

1.14) How does PostgreSQL compare to other + DBMS's?

+ +

There are several ways of measuring software: features, + performance, reliability, support, and price.

+ +
+
Features
+ +
PostgreSQL has most features present in large commercial + DBMS's, like transactions, subselects, triggers, views, foreign + key referential integrity, and sophisticated locking. We have + some features they don't have, like user-defined types, + inheritance, rules, and multi-version concurrency control to + reduce lock contention. We don't have outer joins, but are + working on them.
+
+
+ +
Performance
+ +
PostgreSQL runs in two modes. Normal fsync mode + flushes every completed transaction to disk, guaranteeing that if + the OS crashes or loses power in the next few seconds, all your + data is safely stored on disk. In this mode, we are slower than + most commercial databases, partly because few of them do such + conservative flushing to disk in their default modes. In + no-fsync mode, we are usually faster than commercial + databases, though in this mode, an OS crash could cause data + corruption. We are working to provide an intermediate mode that + suffers less performance overhead than full fsync mode, and will + allow data integrity within 30 seconds of an OS crash.
+
+ In comparison to MySQL or leaner database systems, we are slower + on inserts/updates because we have transaction overhead. Of + course, MySQL doesn't have any of the features mentioned in the + Features section above. We are built for flexibility and + features, though we continue to improve performance through + profiling and source code analysis. There is an interesting Web + page comparing PostgreSQL to MySQL at http://openacs.org/why-not-mysql.html
+ +
+ We handle each user connection by creating a Unix process. + Backend processes share data buffers and locking information. + With multiple CPU's, multiple backends can easily run on + different CPU's.
+
+
+ +
Reliability
+ +
We realize that a DBMS must be reliable, or it is worthless. + We strive to release well-tested, stable code that has a minimum + of bugs. Each release has at least one month of beta testing, and + our release history shows that we can provide stable, solid + releases that are ready for production use. We believe we compare + favorably to other database software in this area.
+
+
+ +
Support
+ +
Our mailing list provides a large group of developers and + users to help resolve any problems encountered. While we can not + guarantee a fix, commercial DBMS's don't always supply a fix + either. Direct access to developers, the user community, manuals, + and the source code often make PostgreSQL support superior to + other DBMS's. There is commercial per-incident support available + for those who need it. (See support FAQ item.)
+
+
+ +
Price
+ +
We are free for all use, both commercial and non-commercial. + You can add our code to your product with no limitations, except + those outlined in our BSD-style license stated above.
+
+
+
+
-

2.2) What tools are available for hooking -PostgreSQL to Web pages?

+

+

User Client Questions

+
-A nice introduction to Database-backed Web pages can be seen at: http://www.webtools.com

+

2.1) Are there ODBC drivers for + PostgreSQL?

-There is also one at -http://www.phone.net/home/mwm/hotlist/.

+

There are two ODBC drivers available, PsqlODBC and OpenLink + ODBC.

-For Web integration, PHP is an excellent interface. It is at -http://www.php.net

+

PsqlODBC is included in the distribution. More information about + it can be gotten from ftp://ftp.PostgreSQL.org/pub/odbc/.

-For complex cases, many use the Perl interface and CGI.pm.

+

OpenLink ODBC can be gotten from http://www.openlinksw.com. It + works with their standard ODBC client software so you'll have + PostgreSQL ODBC available on every client platform they support + (Win, Mac, Unix, VMS).

-A WWW gateway based on WDB using Perl can be downloaded from http://www.eol.ists.ca/~dunlop/wdb-p95 +

They will probably be selling this product to people who need + commercial-quality support, but a freeware version will always be + available. Questions to postgres95@openlink.co.uk.

-

2.3) Does PostgreSQL have a graphical user interface? -A report generator? An embedded query language interface?

+

See also the ODBC chapter + of the Programmer's Guide.

-We have a nice graphical user interface called pgaccess, which is -shipped as part of the distribution. Pgaccess also has a report -generator. The Web page is http://www.flex.ro/pgaccess

+

2.2) What tools are available for hooking + PostgreSQL to Web pages?

-We also include ecpg, which is an embedded SQL query language interface for -C. +

A nice introduction to Database-backed Web pages can be seen at: + http://www.webtools.com

-

2.4) What languages are available to -communicate with PostgreSQL?

+

There is also one at http://www.phone.net/home/mwm/hotlist/.

-We have: -

+

For Web integration, PHP is an excellent interface. It is at http://www.php.net

-
+

For complex cases, many use the Perl interface and CGI.pm.

-

Administrative Questions

+

A WWW gateway based on WDB using Perl can be downloaded from http://www.eol.ists.ca/~dunlop/wdb-p95

+

2.3) Does PostgreSQL have a graphical user + interface? A report generator? An embedded query language + interface?

-

3.1) Why does initdb fail?

+

We have a nice graphical user interface called pgaccess, + which is shipped as part of the distribution. Pgaccess also + has a report generator. The Web page is http://www.flex.ro/pgaccess

-Try these: -

-If you see an error message about oidvector, you definately have -a version mismatch.

+

We also include ecpg, which is an embedded SQL query + language interface for C.

+

2.4) What languages are available to + communicate with PostgreSQL?

-

3.2) How do I install PostgreSQL somewhere -other than /usr/local/pgsql?

+

We have:

-The simplest way is to specify the --prefix option when running configure. -If you forgot to do that, you can edit Makefile.global and change POSTGRESDIR -accordingly, or create a Makefile.custom and define POSTGRESDIR there.

+

+
+
+

Administrative Questions

+
-

3.6) How do I prevent other hosts from -accessing my PostgreSQL database?

+

3.1) Why does initdb fail?

-By default, PostgreSQL only allows connections from the local machine -using Unix domain sockets. Other machines will not be able to connect -unless you add the -i flag to the postmaster, -and enable host-based authentication by modifying the file -$PGDATA/pg_hba.conf accordingly. This will allow TCP/IP connections. -

+

Try these:

-

3.7) Why can't I connect to my database from -another machine?

+

-You should not create database users with user id 0 (root). They will be -unable to access the database. This is a security precaution because -of the ability of users to dynamically link object modules into the -database engine.

+

If you see an error message about oidvector, you + definately have a version mismatch.

+

3.2) How do I install PostgreSQL somewhere + other than /usr/local/pgsql?

-

3.9) All my servers crash under concurrent -table access. Why?

+

The simplest way is to specify the --prefix option when running + configure. If you forgot to do that, you can edit + Makefile.global and change POSTGRESDIR accordingly, or + create a Makefile.custom and define POSTGRESDIR there.

-This problem can be caused by a kernel that is not configured to support -semaphores.

+

3.3) When I start the postmaster, I + get a Bad System Call or core dumped message. Why?

+

It could be a variety of problems, but first check to see that + you have System V extensions installed in your kernel. PostgreSQL + requires kernel support for shared memory and semaphores.

-

3.10) How do I tune the database engine for -better performance?

+

3.4) When I try to start the + postmaster, I get IpcMemoryCreate errors. Why?

-Certainly, indices can speed up queries. The EXPLAIN command -allows you to see how PostgreSQL is interpreting your query, and which -indices are being used.

+

You either do not have shared memory configured properly in your + kernel or you need to enlarge the shared memory available in the + kernel. The exact amount you need depends on your architecture and + how many buffers and backend processes you configure for the + postmaster. For most systems, with default numbers of + buffers and processes, you need a minimum of ~1MB.

-If you are doing a lot of INSERTs, consider doing them in a large -batch using the COPY command. This is much faster than -individual INSERTS. Second, statements not in a BEGIN -WORK/COMMIT transaction block are considered to be in their -own transaction. Consider performing several statements in a single -transaction block. This reduces the transaction overhead. Also -consider dropping and recreating indices when making large data -changes.

+

3.5) When I try to start the + postmaster, I get IpcSemaphoreCreate errors. + Why?

-There are several tuning options. You can disable -fsync() by starting the postmaster with a -o -F -option. This will prevent fsync()'s from flushing to disk after -every transaction.

+

If the error message is IpcSemaphoreCreate: semget failed (No + space left on device) then your kernel is not configured with + enough semaphores. Postgres needs one semaphore per potential + backend process. A temporary solution is to start the + postmaster with a smaller limit on the number of backend + processes. Use -N with a parameter less than the default of + 32. A more permanent solution is to increase your kernel's + SEMMNS and SEMMNI parameters.

-You can also use the postmaster -B option to increase the number of -shared memory buffers used by the backend processes. If you make this -parameter too high, the postmaster may not start because you've exceeded -your kernel's limit on shared memory space. -Each buffer is 8K and the default is 64 buffers.

+

If the error message is something else, you might not have + semaphore support configured in your kernel at all.

-You can also use the backend -S option to increase the maximum amount -of memory used by the backend process for temporary sorts. The -S value -is measured in kilobytes, and the default is 512 (ie, 512K).

+

3.6) How do I prevent other hosts from + accessing my PostgreSQL database?

-You can also use the CLUSTER command to group data in tables to -match an index. See the CLUSTER manual page for more details.

+

By default, PostgreSQL only allows connections from the local + machine using Unix domain sockets. Other machines will not be able + to connect unless you add the -i flag to the + postmaster, and enable host-based authentication by + modifying the file $PGDATA/pg_hba.conf accordingly. This + will allow TCP/IP connections.

+

3.7) Why can't I connect to my database from + another machine?

-

3.11) What debugging features are available?

+

The default configuration allows only unix domain socket + connections from the local machine. To enable TCP/IP connections, + make sure the postmaster has been started with the -i + option, and add an appropriate host entry to the file + pgsql/data/pg_hba.conf.

-PostgreSQL has several features that report status information that can -be valuable for debugging purposes.

+

3.8) Why can't I access the database as the + root user?

-First, by running configure with the --enable-cassert option, many -assert()'s monitor the progress of the backend and halt the program when -something unexpected occurs.

+

You should not create database users with user id 0 (root). They + will be unable to access the database. This is a security + precaution because of the ability of users to dynamically link + object modules into the database engine.

-Both postmaster and postgres have several debug options available. -First, whenever you start the postmaster, make sure you send the -standard output and error to a log file, like: +

3.9) All my servers crash under concurrent + table access. Why?

+ +

This problem can be caused by a kernel that is not configured to + support semaphores.

+ +

3.10) How do I tune the database engine for + better performance?

+ +

Certainly, indices can speed up queries. The + EXPLAIN command allows you to see how PostgreSQL is + interpreting your query, and which indices are being used.

+ +

If you are doing a lot of INSERTs, consider doing + them in a large batch using the COPY command. This + is much faster than individual INSERTS. Second, + statements not in a BEGIN WORK/COMMIT transaction + block are considered to be in their own transaction. Consider + performing several statements in a single transaction block. This + reduces the transaction overhead. Also consider dropping and + recreating indices when making large data changes.

+ +

There are several tuning options. You can disable fsync() + by starting the postmaster with a -o -F option. This + will prevent fsync()'s from flushing to disk after every + transaction.

+ +

You can also use the postmaster -B option to + increase the number of shared memory buffers used by the backend + processes. If you make this parameter too high, the + postmaster may not start because you've exceeded your + kernel's limit on shared memory space. Each buffer is 8K and the + default is 64 buffers.

+ +

You can also use the backend -S option to increase the + maximum amount of memory used by the backend process for temporary + sorts. The -S value is measured in kilobytes, and the + default is 512 (ie, 512K).

+ +

You can also use the CLUSTER command to group + data in tables to match an index. See the CLUSTER + manual page for more details.

+ +

3.11) What debugging features are + available?

+ +

PostgreSQL has several features that report status information + that can be valuable for debugging purposes.

+ +

First, by running configure with the --enable-cassert + option, many assert()'s monitor the progress of the backend + and halt the program when something unexpected occurs.

+ +

Both postmaster and postgres have several debug + options available. First, whenever you start the postmaster, + make sure you send the standard output and error to a log file, + like:

-	cd /usr/local/pgsql
-	./bin/postmaster >server.log 2>&1 &
-

- -This will put a server.log file in the top-level PostgreSQL directory. -This file contains useful information about problems or errors -encountered by the server. Postmaster has a -d option that allows even -more detailed information to be reported. The -d option takes a number -that specifies the debug level. Be warned that high debug level values -generate large log files.

- -If the postmaster is not running, you can actually run the -postgres backend from the command line, and type your SQL statement -directly. This is recommended only for debugging purposes. Note -that a newline terminates the query, not a semicolon. If you have -compiled with debugging symbols, you can use a debugger to see what is -happening. Because the backend was not started from the postmaster, it -is not running in an identical environment and locking/backend -interaction problems may not be duplicated.

- -If the postmaster is running, start psql in one window, -then find the PID of the postgres process used by -psql. Use a debugger to attach to the postgres -PID. You can set breakpoints in the debugger and issue -queries from psql. If you are debugging postgres startup, -you can set PGOPTIONS="-W n", then start psql. This will cause -startup to delay for n seconds so you can attach with the -debugger and trace through the startup sequence.

- -The postgres program has -s, -A, and -t options that can be very useful -for debugging and performance measurements.

- -You can also compile with profiling to see what functions are taking -execution time. The backend profile files will be deposited in the -pgsql/data/base/dbname directory. The client profile file will be put -in the client's current directory.

- - -

3.12) I get 'Sorry, too many clients' when trying -to connect. Why?

- -You need to increase the postmaster's limit on how many concurrent backend -processes it can start.

- -In PostgreSQL 6.5 and up, the default limit is 32 processes. You can -increase it by restarting the postmaster with a suitable -N -value. With the default configuration you can set -N as large as -1024. If you need more, increase MAXBACKENDS in -include/config.h and rebuild. You can set the default value of --N at configuration time, if you like, using configure's ---with-maxbackends switch.

- -Note that if you make -N larger than 32, you must also increase --B beyond its default of 64; -B must be at least twice -N, and -probably should be more than that for best performance. For large -numbers of backend processes, you are also likely to find that you need -to increase various Unix kernel configuration parameters. Things to -check include the maximum size of shared memory blocks, -SHMMAX; the maximum number of semaphores, -SEMMNS and SEMMNI; the maximum number of -processes, NPROC; the maximum number of processes per -user, MAXUPRC; and the maximum number of open files, -NFILE and NINODE. The reason that PostgreSQL -has a limit on the number of allowed backend processes is so -your system won't run out of resources.

- -In PostgreSQL versions prior to 6.5, the maximum number of backends was -64, and changing it required a rebuild after altering the MaxBackendId -constant in include/storage/sinvaladt.h.

- -

3.13) What are the pg_sorttempNNN.NN files in my -database directory?

- -They are temporary files generated by the query executor. For -example, if a sort needs to be done to satisfy an ORDER BY, and -the sort requires more space than the backend's -S parameter allows, -then temporary files are created to hold the extra data.

- -The temporary files should be deleted automatically, but might not if a backend -crashes during a sort. If you have no backends running at the time, -it is safe to delete the pg_tempNNN.NN files.

- -

- -

Operational Questions

- - -

4.1) Why is system confused about -commas, decimal points, and date formats.

- -Check your locale configuration. PostgreSQL uses the locale setting of -the user that ran the postmaster process. There are postgres and psql -SET commands to control the date format. Set those accordingly for -your operating environment.

- - -

4.2) What is the exact difference between -binary cursors and normal cursors?

- -See the DECLARE manual page for a description.

- -

4.3) How do I SELECT only the first few -rows of a query?

- -See the FETCH manual page, or use SELECT ... LIMIT....

- -The entire query may have to be evaluated, even if you only want the -first few rows. Consider a query that has an ORDER BY. -If there is an index that matches the ORDER BY, -PostgreSQL may be able to evaluate only the first few records requested, -or the entire query may have to be evaluated until the desired rows have -been generated.

- -

4.4) How do I get a list of tables or other -things I can see in psql?

- -You can read the source code for psql in file -pgsql/src/bin/psql/psql.c. It contains SQL commands that generate the -output for psql's backslash commands. You can also start psql -with the -E option so it will print out the queries it uses -to execute the commands you give.

- - -

4.5) How do you remove a column from a -table?

+ cd /usr/local/pgsql + ./bin/postmaster >server.log 2>&1 & + -We do not support ALTER TABLE DROP COLUMN, but do -this: +

This will put a server.log file in the top-level PostgreSQL + directory. This file contains useful information about problems or + errors encountered by the server. Postmaster has a -d + option that allows even more detailed information to be reported. + The -d option takes a number that specifies the debug level. + Be warned that high debug level values generate large log + files.

+ +

If the postmaster is not running, you can actually run + the postgres backend from the command line, and type your + SQL statement directly. This is recommended only for + debugging purposes. Note that a newline terminates the query, not a + semicolon. If you have compiled with debugging symbols, you can use + a debugger to see what is happening. Because the backend was not + started from the postmaster, it is not running in an + identical environment and locking/backend interaction problems may + not be duplicated.

+ +

If the postmaster is running, start psql in one + window, then find the PID of the postgres + process used by psql. Use a debugger to attach to the + postgres PID. You can set breakpoints in the + debugger and issue queries from psql. If you are debugging + postgres startup, you can set PGOPTIONS="-W n", then start + psql. This will cause startup to delay for n seconds + so you can attach with the debugger and trace through the startup + sequence.

+ +

The postgres program has -s, -A, and -t + options that can be very useful for debugging and performance + measurements.

+ +

You can also compile with profiling to see what functions are + taking execution time. The backend profile files will be deposited + in the pgsql/data/base/dbname directory. The client profile + file will be put in the client's current directory.

+ +

3.12) I get 'Sorry, too many clients' when + trying to connect. Why?

+ +

You need to increase the postmaster's limit on how many + concurrent backend processes it can start.

+ +

In PostgreSQL 6.5 and up, the default limit is 32 processes. You + can increase it by restarting the postmaster with a suitable + -N value. With the default configuration you can set + -N as large as 1024. If you need more, increase + MAXBACKENDS in include/config.h and rebuild. + You can set the default value of -N at configuration time, + if you like, using configure's --with-maxbackends + switch.

+ +

Note that if you make -N larger than 32, you must also + increase -B beyond its default of 64; -B must be at + least twice -N, and probably should be more than that for + best performance. For large numbers of backend processes, you are + also likely to find that you need to increase various Unix kernel + configuration parameters. Things to check include the maximum size + of shared memory blocks, SHMMAX; the maximum number + of semaphores, SEMMNS and SEMMNI; the + maximum number of processes, NPROC; the maximum + number of processes per user, MAXUPRC; and the + maximum number of open files, NFILE and + NINODE. The reason that PostgreSQL has a limit on + the number of allowed backend processes is so your system won't run + out of resources.

+ +

In PostgreSQL versions prior to 6.5, the maximum number of + backends was 64, and changing it required a rebuild after altering + the MaxBackendId constant in + include/storage/sinvaladt.h.

+ +

3.13) What are the pg_sorttempNNN.NN + files in my database directory?

+ +

They are temporary files generated by the query executor. For + example, if a sort needs to be done to satisfy an ORDER + BY, and the sort requires more space than the backend's + -S parameter allows, then temporary files are created to + hold the extra data.

+ +

The temporary files should be deleted automatically, but might + not if a backend crashes during a sort. If you have no backends + running at the time, it is safe to delete the pg_tempNNN.NN + files.

+
+ +
+

Operational Questions

+
+ +

4.1) Why is system confused about commas, + decimal points, and date formats.

+ +

Check your locale configuration. PostgreSQL uses the locale + setting of the user that ran the postmaster process. There + are postgres and psql SET commands to control the date format. Set + those accordingly for your operating environment.

+ +

4.2) What is the exact difference between + binary cursors and normal cursors?

+ +

See the DECLARE manual page for a + description.

+ +

4.3) How do I SELECT only the + first few rows of a query?

+ +

See the FETCH manual page, or use SELECT ... + LIMIT....

+ +

The entire query may have to be evaluated, even if you only want + the first few rows. Consider a query that has an ORDER + BY. If there is an index that matches the ORDER + BY, PostgreSQL may be able to evaluate only the first few + records requested, or the entire query may have to be evaluated + until the desired rows have been generated.

+ +

4.4) How do I get a list of tables or other + things I can see in psql?
+

+ +

You can read the source code for psql in file + pgsql/src/bin/psql/psql.c. It contains SQL commands that + generate the output for psql's backslash commands. You can also + start psql with the -E option so it will print out + the queries it uses to execute the commands you give.

+ +

4.5) How do you remove a column from a + table?

+ +

We do not support ALTER TABLE DROP COLUMN, but do + this:

-	SELECT ...  -- select all columns but the one you want to remove
-	INTO TABLE new_table
-	FROM old_table;
-	DROP TABLE old_table;
-	ALTER TABLE new_table RENAME TO old_table;
-

- - - - -

4.6) What is the maximum size for a -row, table, database?

+ SELECT ... -- select all columns but the one you want to remove + INTO TABLE new_table + FROM old_table; + DROP TABLE old_table; + ALTER TABLE new_table RENAME TO old_table; + -These are the limits: +

4.6) What is the maximum size for a row, + table, database?

+

These are the limits:

-Maximum size for a database? 	         unlimited (60GB databases exist)
+Maximum size for a database?             unlimited (60GB databases exist)
 Maximum size for a table?                unlimited on all operating systems
 Maximum size for a row?                  8k, configurable to 32k
-Maximum number of rows in a table?	 unlimited
+Maximum number of rows in a table?   unlimited
 Maximum number of columns in a table?    unlimited
-Maximum number of indexes on a table?	 unlimited
+Maximum number of indexes on a table?    unlimited
+ Of course, these are not actually unlimited, but limited to + available disk space. -Of course, these are not actually unlimited, but limited to available -disk space.

- -To change the maximum row size, edit include/config.h and change -BLCKSZ. To use attributes larger than 8K, you can also -use the large object interface.

- -The row length limit will be removed in 7.1.

- +

To change the maximum row size, edit include/config.h and + change BLCKSZ. To use attributes larger than 8K, you + can also use the large object interface.

-

4.7) How much database disk space is required to -store data from a typical text file?

+

The row length limit will be removed in 7.1.

-A PostgreSQL database may need six-and-a-half times the disk space -required to store the data in a flat file.

+

4.7) How much database disk space is required + to store data from a typical text file?
+

-Consider a file of 300,000 lines with two integers on each line. The -flat file is 2.4MB. The size of the PostgreSQL database file containing -this data can be estimated at 14MB: +

A PostgreSQL database may need six-and-a-half times the disk + space required to store the data in a flat file.

+

Consider a file of 300,000 lines with two integers on each line. + The flat file is 2.4MB. The size of the PostgreSQL database file + containing this data can be estimated at 14MB:

     36 bytes: each row header (approximate)
    + 8 bytes: two int fields @ 4 bytes each
@@ -890,106 +930,107 @@ this data can be estimated at 14MB:
       171 rows per page
 
 1755 database pages * 8192 bytes per page  =  14,376,960 bytes (14MB)
-

- -Indexes do not require as much overhead, but do contain the data that is -being indexed, so they can be large also.

- -

4.8) How do I find out what indices or -operations are defined in the database?

- -psql has a variety of backslash commands to show such information. Use -\? to see them.

- -Also try the file pgsql/src/tutorial/syscat.source. It -illustrates many of the SELECTs needed to get information from -the database system tables.

- - -

4.9) My queries are slow or don't make -use of the indexes. Why?

- -PostgreSQL does not automatically maintain statistics. VACUUM -must be run to update the statistics. After -statistics are updated, the optimizer knows how many rows in the table, -and can better decide if it should use indices. Note that the optimizer -does not use indices in cases when the table is small because a -sequential scan would be faster.

- -For column-specific optimization statistics, use VACUUM -ANALYZE. VACUUM ANALYZE is important for complex -multijoin queries, so the optimizer can estimate the number of rows -returned from each table, and choose the proper join order. The backend -does not keep track of column statistics on its own, so VACUUM -ANALYZE must be run to collect them periodically.

- -Indexes are usually not used for ORDER BY operations: a -sequential scan followed by an explicit sort is faster than an indexscan -of all tuples of a large table, because it takes fewer disk accesses. -

- -When using wild-card operators such as LIKE or ~, indices can -only be used if the beginning of the search is anchored to the start of -the string. So, to use indices, LIKE searches should not -begin with %, and ~(regular expression searches) should -start with ^. - -

4.10) How do I see how the query optimizer is -evaluating my query?

- -See the EXPLAIN manual page.

- -

4.11) What is an R-tree index?

- -An R-tree index is used for indexing spatial data. A hash index can't -handle range searches. A B-tree index only handles range searches in a -single dimension. R-tree's can handle multi-dimensional data. For -example, if an R-tree index can be built on an attribute of type point, -the system can more efficiently answer queries such as "select all points -within a bounding rectangle."

- -The canonical paper that describes the original R-tree design is:

- -Guttman, A. "R-trees: A Dynamic Index Structure for Spatial Searching." -Proc of the 1984 ACM SIGMOD Int'l Conf on Mgmt of Data, 45-57.

- -You can also find this paper in Stonebraker's "Readings in Database -Systems".

- -Built-in R-trees can handle polygons and boxes. In theory, R-trees can -be extended to handle higher number of dimensions. In practice, -extending R-trees requires a bit of work and we don't currently have any -documentation on how to do it.

- - -

4.12) What is Genetic Query -Optimization?

- -The GEQO module speeds query -optimization when joining many tables by means of a Genetic -Algorithm (GA). It allows the handling of large join queries through -nonexhaustive search.

- -

4.13) How do I do regular expression searches and -case-insensitive regular expression searches?

+ -The ~ operator does regular expression matching, and ~* -does case-insensitive regular expression matching. There is no -case-insensitive variant of the LIKE operator, but you can get the -effect of case-insensitive LIKE with this: +

Indexes do not require as much overhead, but do contain the data + that is being indexed, so they can be large also.

+ +

4.8) How do I find out what indices or + operations are defined in the database?

+ +

psql has a variety of backslash commands to show such + information. Use \? to see them.

+ +

Also try the file pgsql/src/tutorial/syscat.source. It + illustrates many of the SELECTs needed to get + information from the database system tables.

+ +

4.9) My queries are slow or don't make use of + the indexes. Why?

+ +

PostgreSQL does not automatically maintain statistics. + VACUUM must be run to update the statistics. After + statistics are updated, the optimizer knows how many rows in the + table, and can better decide if it should use indices. Note that + the optimizer does not use indices in cases when the table is small + because a sequential scan would be faster.

+ +

For column-specific optimization statistics, use VACUUM + ANALYZE. VACUUM ANALYZE is important for + complex multijoin queries, so the optimizer can estimate the number + of rows returned from each table, and choose the proper join order. + The backend does not keep track of column statistics on its own, so + VACUUM ANALYZE must be run to collect them + periodically.

+ +

Indexes are usually not used for ORDER BY + operations: a sequential scan followed by an explicit sort is + faster than an indexscan of all tuples of a large table, because it + takes fewer disk accesses.

+ +

When using wild-card operators such as LIKE or + ~, indices can only be used if the beginning of the search + is anchored to the start of the string. So, to use indices, + LIKE searches should not begin with %, and + ~(regular expression searches) should start with + ^.

+ +

4.10) How do I see how the query optimizer + is evaluating my query?

+ +

See the EXPLAIN manual page.

+ +

4.11) What is an R-tree index?

+ +

An R-tree index is used for indexing spatial data. A hash index + can't handle range searches. A B-tree index only handles range + searches in a single dimension. R-tree's can handle + multi-dimensional data. For example, if an R-tree index can be + built on an attribute of type point, the system can more + efficiently answer queries such as "select all points within a + bounding rectangle."

+ +

The canonical paper that describes the original R-tree design + is:

+ +

Guttman, A. "R-trees: A Dynamic Index Structure for Spatial + Searching." Proc of the 1984 ACM SIGMOD Int'l Conf on Mgmt of Data, + 45-57.

+ +

You can also find this paper in Stonebraker's "Readings in + Database Systems".

+ +

Built-in R-trees can handle polygons and boxes. In theory, + R-trees can be extended to handle higher number of dimensions. In + practice, extending R-trees requires a bit of work and we don't + currently have any documentation on how to do it.

+ +

4.12) What is Genetic Query + Optimization?

+ +

The GEQO module speeds query optimization when joining many + tables by means of a Genetic Algorithm (GA). It allows the handling + of large join queries through nonexhaustive search.

+ +

4.13) How do I do regular expression + searches and case-insensitive regular expression searches?

+ +

The ~ operator does regular expression matching, and + ~* does case-insensitive regular expression matching. There + is no case-insensitive variant of the LIKE operator, but you can + get the effect of case-insensitive LIKE with + this:

-	WHERE lower(textfield) LIKE lower(pattern)
+    WHERE lower(textfield) LIKE lower(pattern)
-

4.14) In a query, how do I detect if a field -is NULL?

- -You test the column with IS NULL and IS NOT NULL.

- +

4.14) In a query, how do I detect if a field + is NULL?

-

4.15) What is the difference between the -various character types?

+

You test the column with IS NULL and IS NOT NULL.

+

4.15) What is the difference between the + various character types?

 Type            Internal Name   Notes
 --------------------------------------------------
@@ -998,103 +1039,110 @@ CHAR(#)         bpchar          blank padded to the specified fixed length
 VARCHAR(#)      varchar         size specifies maximum length, no padding
 TEXT            text            no specific upper limit on length
 BYTEA           bytea           variable-length byte array (null-safe)
-

+ -You will see the internal name when examining system catalogs -and in some error messages.

- -The last four types above are "varlena" types (i.e., the first four -bytes on disk are the length, followed by the data). Thus the actual -space used is slightly greater than the declared size. However, these -data types are also subject to compression or being stored out-of-line -by TOAST, so the space on disk might also be less than expected.

+

You will see the internal name when examining system catalogs + and in some error messages.

+

The last four types above are "varlena" types (i.e., the first + four bytes on disk are the length, followed by the data). Thus the + actual space used is slightly greater than the declared size. + However, these data types are also subject to compression or being + stored out-of-line by TOAST, so the space on disk might also be + less than expected.

-

4.16.1) How do I create a -serial/auto-incrementing field?

+

4.16.1) How do I create a + serial/auto-incrementing field?

-PostgreSQL supports a SERIAL data type. It auto-creates a -sequence and index on the column. For example, this: +

PostgreSQL supports a SERIAL data type. It + auto-creates a sequence and index on the column. For example, + this:

-	CREATE TABLE person ( 
-		id   SERIAL, 
-		name TEXT 
-	);
+    CREATE TABLE person ( 
+        id   SERIAL, 
+        name TEXT 
+    );
-is automatically translated into this: + is automatically translated into this: 
-	CREATE SEQUENCE person_id_seq;
-	CREATE TABLE person ( 
-		id   INT4 NOT NULL DEFAULT nextval('person_id_seq'),
-		name TEXT 
-	);
-	CREATE UNIQUE INDEX person_id_key ON person ( id );
+    CREATE SEQUENCE person_id_seq;
+    CREATE TABLE person ( 
+        id   INT4 NOT NULL DEFAULT nextval('person_id_seq'),
+        name TEXT 
+    );
+    CREATE UNIQUE INDEX person_id_key ON person ( id );
-See the create_sequence manual page for more information about sequences. - -You can also use each row's OID field as a unique value. However, if -you need to dump and reload the database, you need to use pg_dump's -o -option or COPY WITH OIDS option to preserve the OIDs.

- -Numbering Rows. - -

4.16.2) How do I get the value of a -SERIAL insert?

-One approach is to to retrieve the next SERIAL value from the sequence object with the nextval() function before inserting and then insert it explicitly. Using the example table in 4.16.1, that might look like this: + See the create_sequence manual page for more information + about sequences. You can also use each row's OID field as a + unique value. However, if you need to dump and reload the database, + you need to use pg_dump's -o option or COPY WITH + OIDS option to preserve the OIDs. + +

Numbering + Rows.

+ +

4.16.2) How do I get the value of a + SERIAL insert?

+ +

One approach is to to retrieve the next SERIAL value from the + sequence object with the nextval() function before + inserting and then insert it explicitly. Using the example table in + 4.16.1, that might look like this:

-	$newSerialID = nextval('person_id_seq');
-	INSERT INTO person (id, name) VALUES ($newSerialID, 'Blaise Pascal');
+    $newSerialID = nextval('person_id_seq');
+    INSERT INTO person (id, name) VALUES ($newSerialID, 'Blaise Pascal');
- -You would then also have the new value stored in -$newSerialID for use in other queries (e.g., as a foreign -key to the person table). Note that the name of the -automatically created SEQUENCE object will be named -<table>_<serialcolumn>_seq, where -table and serialcolumn are the names of your table and -your SERIAL column, respectively. - -

-Alternatively, you could retrieve the assigned SERIAL value with the currval() function after it was inserted by default, e.g., + You would then also have the new value stored in + $newSerialID for use in other queries (e.g., as a + foreign key to the person table). Note that the name + of the automatically created SEQUENCE object will be named + <table>_<serialcolumn>_seq, where + table and serialcolumn are the names of your table + and your SERIAL column, respectively. + +

Alternatively, you could retrieve the assigned SERIAL value with + the currval() function after it was inserted by + default, e.g.,

-	INSERT INTO person (name) VALUES ('Blaise Pascal');
-	$newID = currval('person_id_seq');
+    INSERT INTO person (name) VALUES ('Blaise Pascal');
+    $newID = currval('person_id_seq');
- -Finally, you could use the OID -returned from the INSERT statement to look up the default value, though -this is probably the least portable approach. In Perl, using DBI with -Edmund Mergl's DBD::Pg module, the oid value is made available via -$sth->{pg_oid_status} after $sth->execute(). - -

4.16.3) Don't currval() and nextval() lead to -a race condition with other users?

- -No. This is handled by the backends. - - -

4.17) What is an OID? What is a -TID?

- -OIDs are PostgreSQL's answer to unique row ids. Every -row that is created in PostgreSQL gets a unique OID. All -OIDs generated during initdb are less than 16384 -(from backend/access/transam.h). All user-created -OIDs are equal to or greater than this. By default, all -these OIDs are unique not only within a table or -database, but unique within the entire PostgreSQL installation.

- -PostgreSQL uses OIDs in its internal system tables to link rows between -tables. These OIDs can be used to identify specific user rows and used -in joins. It is recommended you use column type OID to -store OID -values. You can create an index on the OID field for faster access.

- -Oids are assigned to all new rows from a central area that is used by -all databases. If you want to change the OID to something else, or if -you want to make a copy of the table, with the original OID's, there is -no reason you can't do it: - + Finally, you could use the OID + returned from the INSERT statement to look up the default value, + though this is probably the least portable approach. In Perl, using + DBI with Edmund Mergl's DBD::Pg module, the oid value is made + available via $sth->{pg_oid_status} after + $sth->execute(). + +

4.16.3) Don't currval() and + nextval() lead to a race condition with other users?

+ +

No. This is handled by the backends.

+ +

4.17) What is an OID? What is + a TID?

+ +

OIDs are PostgreSQL's answer to unique row ids. + Every row that is created in PostgreSQL gets a unique + OID. All OIDs generated during + initdb are less than 16384 (from + backend/access/transam.h). All user-created + OIDs are equal to or greater than this. By default, + all these OIDs are unique not only within a table or + database, but unique within the entire PostgreSQL installation.

+ +

PostgreSQL uses OIDs in its internal system + tables to link rows between tables. These OIDs can + be used to identify specific user rows and used in joins. It is + recommended you use column type OID to store + OID values. You can create an index on the + OID field for faster access.

+ +

Oids are assigned to all new rows from a central + area that is used by all databases. If you want to change the + OID to something else, or if you want to make a copy + of the table, with the original OID's, there is no + reason you can't do it:

         CREATE TABLE new_table(old_oid oid, mycol int);
         SELECT old_oid, mycol INTO new FROM old;
@@ -1102,162 +1150,180 @@ no reason you can't do it:
         DELETE FROM new;
         COPY new WITH OIDS FROM '/tmp/pgtable';
 
-

+ -OIDs are stored as 4-byte integers, and will overflow -at 4 billion. No one has reported this ever happening, and we plan to -have the limit removed before anyone does.

+

OIDs are stored as 4-byte integers, and will + overflow at 4 billion. No one has reported this ever happening, and + we plan to have the limit removed before anyone does.

-TIDs are used to identify specific physical rows with block and offset -values. Tids change after rows are modified or reloaded. They are used -by index entries to point to physical rows.

+

TIDs are used to identify specific physical rows + with block and offset values. Tids change after rows are modified + or reloaded. They are used by index entries to point to physical + rows.

+

4.18) What is the meaning of some of the + terms used in PostgreSQL?

-

4.18) What is the meaning of some of the terms -used in PostgreSQL?

+

Some of the source code and older documentation use terms that + have more common usage. Here are some:

-Some of the source code and older documentation use terms that have more -common usage. Here are some: + + +

A list of general database terms can be found at: http://www.comptechnews.com/~reaster/dbdesign.html

-Depending on your shell, only one of these may succeed, but it will set -your process data segment limit much higher and perhaps allow the query -to complete. This command applies to the current process, and all -subprocesses created after the command is run. If you are having a problem -with the SQL client because the backend is returning too much data, try -it before starting the client.

- -

4.20) How do I tell what PostgreSQL version I -am running?

- -From psql, type select version();

- -

4.21) My large-object operations get invalid -large obj descriptor. Why?

- -You need to put BEGIN WORK and COMMIT - around any use of a large object handle, that is, -surrounding lo_open ... lo_close.

- -Currently PostgreSQL enforces the rule by closing large object handles -at transaction commit. So the first attempt to do anything with the -handle will draw invalid large obj descriptor. So code that used -to work (at least most of the time) will now generate that error message -if you fail to use a transaction.

- -If you are using a client interface like ODBC you may need to set -auto-commit off.

- -

4.22) How do I create a column that will default to the -current time?

-Use now(): -

-	CREATE TABLE test (x int, modtime timestamp DEFAULT now() );
-
-

-

4.23) Why are my subqueries using -IN so slow?

-Currently, we join subqueries to outer queries by sequentially scanning -the result of the subquery for each row of the outer query. A workaround -is to replace IN with EXISTS: -

-	SELECT *
-	FROM tab
-	WHERE col1 IN (SELECT col2 FROM TAB2)
-
-to: -
-	SELECT *
-	FROM tab
-	WHERE EXISTS (SELECT col2 FROM TAB2 WHERE col1 = col2)
-
 -We hope to fix this limitation in a future release. - -

4.24) How do I do an outer join?

-PostgreSQL does not support outer joins in the current release. They can -be simulated using UNION and NOT IN. For -example, when joining tab1 and tab2, the following query -does an outer join of the two tables: +

4.19) Why do I get the error "FATAL: + palloc failure: memory exhausted?"
+

+ +

It is possible you have run out of virtual memory on your + system, or your kernel has a low limit for certain resources. Try + this before starting the postmaster:

-	SELECT tab1.col1, tab2.col2
-	FROM tab1, tab2
-	WHERE tab1.col1 = tab2.col1
-	UNION ALL
-	SELECT tab1.col1, NULL
-	FROM tab1
-	WHERE tab1.col1 NOT IN (SELECT tab2.col1 FROM tab2)
-	ORDER BY tab1.col1
+    ulimit -d 65536
+    limit datasize 64m
+ Depending on your shell, only one of these may succeed, but it will + set your process data segment limit much higher and perhaps allow + the query to complete. This command applies to the current process, + and all subprocesses created after the command is run. If you are + having a problem with the SQL client because the backend is + returning too much data, try it before starting the client. + +

4.20) How do I tell what PostgreSQL version + I am running?
+

+ +

From psql, type select version();

+ +

4.21) My large-object operations get + invalid large obj descriptor. Why?
+

-
+

You need to put BEGIN WORK and COMMIT + around any use of a large object handle, that is, surrounding + lo_open ... lo_close.

-

Extending PostgreSQL

+

Currently PostgreSQL enforces the rule by closing large object + handles at transaction commit. So the first attempt to do anything + with the handle will draw invalid large obj descriptor. So + code that used to work (at least most of the time) will now + generate that error message if you fail to use a transaction.

+

If you are using a client interface like ODBC you may need to + set auto-commit off.

+ +

4.22) How do I create a column that will + default to the current time?
+

+ +

Use now():

+
+CREATE TABLE test (x int, modtime timestamp DEFAULT now() );
+
+
-

5.1) I wrote a user-defined function. When -I run it in psql, why does it dump core?

+

4.23) Why are my subqueries using + IN so slow?
+

-The problem could be a number of things. Try testing your user-defined -function in a stand-alone test program first. +

Currently, we join subqueries to outer queries by sequentially + scanning the result of the subquery for each row of the outer + query. A workaround is to replace IN with + EXISTS:

+
+SELECT *
+    FROM tab
+    WHERE col1 IN (SELECT col2 FROM TAB2)
+
+
+ to: +
+SELECT *
+    FROM tab
+    WHERE EXISTS (SELECT col2 FROM TAB2 WHERE col1 = col2)
+
+
+ We hope to fix this limitation in a future release. -

5.2) What does the message -"NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!" mean?

+

4.24) How do I do an outer join?
+

-You are pfree'ing something that was not palloc'ed. -Beware of mixing malloc/free and palloc/pfree. +

PostgreSQL does not support outer joins in the current release. + They can be simulated using UNION and NOT + IN. For example, when joining tab1 and tab2, + the following query does an outer join of the two + tables:

+
+    SELECT tab1.col1, tab2.col2
+    FROM tab1, tab2
+    WHERE tab1.col1 = tab2.col1
+    UNION ALL
+    SELECT tab1.col1, NULL
+    FROM tab1
+    WHERE tab1.col1 NOT IN (SELECT tab2.col1 FROM tab2)
+    ORDER BY tab1.col1
+
+
+
+

Extending PostgreSQL

+
-

5.3) How can I contribute some nifty new types and -functions to PostgreSQL?

+

5.1) I wrote a user-defined function. When I + run it in psql, why does it dump core?

+

The problem could be a number of things. Try testing your + user-defined function in a stand-alone test program first.

-Send your extensions to the pgsql-hackers mailing list, and they will -eventually end up in the contrib/ subdirectory.

+

5.2) What does the message + "NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!" + mean?

+

You are pfree'ing something that was not + palloc'ed. Beware of mixing malloc/free and + palloc/pfree.

-

5.4) How do I write a C function to return a -tuple?

+

5.3) How can I contribute some nifty new + types and functions to PostgreSQL?

-This requires wizardry so extreme that the authors have never -tried it, though in principle it can be done.

+

Send your extensions to the pgsql-hackers mailing list, + and they will eventually end up in the contrib/ + subdirectory.

-

5.5) I have changed a source file. Why does the -recompile not see the change?

+

5.4) How do I write a C function to return a + tuple?

-The Makefiles do not have the proper dependencies for include files. You -have to do a make clean and then another make.

+

This requires wizardry so extreme that the authors have never + tried it, though in principle it can be done.

+

5.5) I have changed a source file. Why does + the recompile not see the change?

- +

The Makefiles do not have the proper dependencies for + include files. You have to do a make clean and then another + make.

+