+Frequently Asked Questions (FAQ) for PostgreSQL
+
+Last updated: Sun Feb 1 16:13:28 EST 1998
+
+Current maintainer: Bruce Momjian (maillist@candle.pha.pa.us)
+
+The most recent version of this document can be viewed at the postgreSQL Web
+site, http://postgreSQL.org.
+
+Linux-specific questions are answered in
+http://postgreSQL.org/docs/faq-linux.shtml.
+
+Irix-specific questions are answered in
+http://postgreSQL.org/docs/faq-irix.shtml.
+
+ ------------------------------------------------------------------------
- Frequently Asked Questions (FAQ) for PostgreSQL
-
- Last updated: Sun Feb 1 16:13:28 EST 1998
-
- Current maintainer: Bruce Momjian (maillist@candle.pha.pa.us)
-
- The most recent version of this document can be viewed at the
- postgreSQL Web site, http://postgreSQL.org.
-
- Linux-specific questions are answered in
- http://postgreSQL.org/docs/FAQ-linux.shtml.
-
- Irix-specific questions are answered in
- http://postgreSQL.org/docs/FAQ-irix.shtml.
- _________________________________________________________________
-
Questions answered:
- 1) General questions
-
- 1.1) What is PostgreSQL?
- 1.2) What does PostgreSQL run on?
- 1.3) Where can I get PostgreSQL?
- 1.4) What's the copyright on PostgreSQL?
- 1.5) Support for PostgreSQL
- 1.6) Latest release of PostgreSQL
- 1.7) Is there a commercial version of PostgreSQL?
- 1.8) What documentation is available for PostgreSQL?
- 1.9) What version of SQL does PostgreSQL use?
- 1.10) Does PostgreSQL work with databases from earlier versions of
- postgres?
- 1.11) Are there ODBC drivers for PostgreSQL?
- 1.12) What tools are available for hooking postgres to Web pages?
- 1.13) Does PostgreSQL have a graphical user interface? A report
- generator? A embedded query language interface?
- 1.14) What is a good book to learn SQL?
-
- 2) Installation/Configuration questions
-
- 2.1) initdb doesn't run
- 2.2) when I start up the postmaster, I get "FindBackend: could not
- find a backend to execute..." "postmaster: could not find backend to
- execute..."
- 2.3) The system seems to be confused about commas, decimal points, and
- date formats.
- 2.4) How do I install PostgreSQL somewhere other than
- /usr/local/pgsql?
- 2.5) When I run postmaster, I get a Bad System Call core dumped
- message.
- 2.6) When I try to start the postmaster, I get IpcMemoryCreate errors.
- 2.7) I have changed a source file, but a recompile does not see the
- change?
- 2.8) How do I prevent other hosts from accessing my PostgreSQL
- 2.9) I can't access the database as the 'root' user.
- 2.10) All my servers crash under concurrent table access. Why?
- 2.11) How do I tune the database engine for better performance?
- 2.12) What debugging features are available in PostgreSQL?
- 2.13) How do I enable more than 32 concurrent backends?
-
- 3) Operational questions
-
- 3.1) Does PostgreSQL support nested subqueries?
- 3.2) I've having a lot of problems using rules.
- 3.3) I can't seem to write into the middle of large objects reliably.
- 3.4) How can I write client applications to PostgreSQL?
- 3.5) How do I set up a pg_group?
- 3.6) What is the exact difference between binary cursors and normal
- cursors?
- 3.7) What is a R-tree index and what is it used for?
- 3.8) What is the maximum size for a tuple?
- 3.9) I defined indices but my queries don't seem to make use of them.
- Why?
- 3.10) How do I do regular expression searches? case-insensitive regexp
- searching?
- 3.11) I experienced a server crash during a vacuum. How do I remove
- the lock file?
- 3.12) What is the difference between the various character types?
- 3.13) In a query, how do I detect if a field is NULL?
- 3.14) How do I see how the query optimizer is evaluating my query?
- 3.15) How do I create a serial field?
- 3.16) What are the pg_psort.XXX files in my database directory?
- 3.17) Why can't I connect to my database from another machine?
- 3.18) How do I find out what indexes or operations are defined in the
- database?
- 3.19) What is the time-warp feature and how does it relate to vacuum?
- 3.20) What is an oid? What is a tid?
- 3.21) What is the meaning of some of the terms used in Postgres?
- 3.22) What is Genetic Query Optimization?
- 3.23) How do you remove a column from a table?
- 3.24) How do SELECT only the first few rows of a query?
- 3.25) Why can't I create a column named "time"?
- 3.26) How much database disk space is required to store data from a
- typical flat file?
-
- 4) Questions about extending PostgreSQL
-
- 4.1) I wrote a user-defined function and when I run it in psql, it
- dumps core.
- 4.2) I get messages of the type NOTICE:PortalHeapMemoryFree:
- 0x402251d0
- 4.3) I've written some nifty new types and functions for PostgreSQL.
- 4.4) How do I write a C function to return a tuple?
-
- 5) Bugs
-
- 5.1) How do I make a bug report?
- _________________________________________________________________
-
+1) General questions
+
+1.1) What is PostgreSQL?
+1.2) What does PostgreSQL run on?
+1.3) Where can I get PostgreSQL?
+1.4) What's the copyright on PostgreSQL?
+1.5) Support for PostgreSQL
+1.6) Latest release of PostgreSQL
+1.7) Is there a commercial version of PostgreSQL?
+1.8) What documentation is available for PostgreSQL?
+1.9) What version of SQL does PostgreSQL use?
+1.10) Does PostgreSQL work with databases from earlier versions of postgres?
+1.11) Are there ODBC drivers for PostgreSQL?
+1.12) What tools are available for hooking postgres to Web pages?
+1.13) Does PostgreSQL have a graphical user interface? A report generator? A
+embedded query language interface?
+1.14) What is a good book to learn SQL?
+
+2) Installation/Configuration questions
+
+2.1) initdb doesn't run
+2.2) when I start up the postmaster, I get "FindBackend: could not find a
+backend to execute..." "postmaster: could not find backend to execute..."
+2.3) The system seems to be confused about commas, decimal points, and date
+formats.
+2.4) How do I install PostgreSQL somewhere other than /usr/local/pgsql?
+2.5) When I run postmaster, I get a Bad System Call core dumped message.
+2.6) When I try to start the postmaster, I get IpcMemoryCreate errors.
+2.7) I have changed a source file, but a recompile does not see the change?
+2.8) How do I prevent other hosts from accessing my PostgreSQL
+2.9) I can't access the database as the 'root' user.
+2.10) All my servers crash under concurrent table access. Why?
+2.11) How do I tune the database engine for better performance?
+2.12) What debugging features are available in PostgreSQL?
+2.13) How do I enable more than 32 concurrent backends?
+
+3) Operational questions
+
+3.1) Does PostgreSQL support nested subqueries?
+3.2) I've having a lot of problems using rules.
+3.3) I can't seem to write into the middle of large objects reliably.
+3.4) How can I write client applications to PostgreSQL?
+3.5) How do I set up a pg_group?
+3.6) What is the exact difference between binary cursors and normal cursors?
+3.7) What is a R-tree index and what is it used for?
+3.8) What is the maximum size for a tuple?
+3.9) I defined indices but my queries don't seem to make use of them. Why?
+3.10) How do I do regular expression searches? case-insensitive regexp
+searching?
+3.11) I experienced a server crash during a vacuum. How do I remove the lock
+file?
+3.12) What is the difference between the various character types?
+3.13) In a query, how do I detect if a field is NULL?
+3.14) How do I see how the query optimizer is evaluating my query?
+3.15) How do I create a serial field?
+3.16) What are the pg_psort.XXX files in my database directory?
+3.17) Why can't I connect to my database from another machine?
+3.18) How do I find out what indexes or operations are defined in the
+database?
+3.19) What is the time-warp feature and how does it relate to vacuum?
+3.20) What is an oid? What is a tid?
+3.21) What is the meaning of some of the terms used in Postgres?
+3.22) What is Genetic Query Optimization?
+3.23) How do you remove a column from a table?
+3.24) How do SELECT only the first few rows of a query?
+3.25) Why can't I create a column named "time"?
+3.26) How much database disk space is required to store data from a typical
+flat file?
+
+4) Questions about extending PostgreSQL
+
+4.1) I wrote a user-defined function and when I run it in psql, it dumps
+core.
+4.2) I get messages of the type NOTICE:PortalHeapMemoryFree: 0x402251d0
+4.3) I've written some nifty new types and functions for PostgreSQL.
+4.4) How do I write a C function to return a tuple?
+
+5) Bugs
+
+5.1) How do I make a bug report?
+
+ ------------------------------------------------------------------------
+
Section 1: 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 being 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 current and future 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.
-
- 1.2) What does PostgreSQL run on?
-
- The authors have compiled and tested PostgreSQL on the following
- platforms(some of these compiles require gcc 2.7.0):
- * aix - IBM on AIX 3.2.5 or 4.x
- * alpha - DEC Alpha AXP on Digital Unix 2.0, 3.2, 4.0
- * BSD44_derived - OSs derived from 4.4-lite BSD (NetBSD, FreeBSD)
- * bsdi - BSD/OS 2.0, 2.01, 2.1, 3.0
- * dgux - DG/UX 5.4R4.11
- * hpux - HP PA-RISC on HP-UX 9.0, 10
- * i386_solaris - i386 Solaris
- * irix5 - SGI MIPS on IRIX 5.3
- * linux - Intel x86 on Linux 2.0 and Linux ELF SPARC on Linux ELF
- PPC on Linux Elf (For non-ELF Linux, see LINUX_ELF below).
- * sco - SCO 3.2v5
- * sparc_solaris - SUN SPARC on Solaris 2.4, 2.5, 2.5.1
- * sunos4 - SUN SPARC on SunOS 4.1.3
- * svr4 - Intel x86 on Intel SVR4 and MIPS
- * ultrix4 - DEC MIPS on Ultrix 4.4
-
- The following platforms have known problems/bugs:
- * nextstep - Motorola MC68K or Intel x86 on NeXTSTEP 3.2
-
- 1.3) Where can I get PostgreSQL?
-
- The primary anonymous ftp site for PostgreSQL is:
- * ftp://ftp.postgreSQL.org/pub
-
- A mirror site exists at:
- * ftp://postgres95.vnet.net/pub/postgres95
- * ftp://ftp.luga.or.at/pub/postgres95
- * ftp://cal011111.student.utwente.nl/pub/postgres95
- * ftp://ftp.uni-trier.de/pub/database/rdbms/postgres/postgres95
- * ftp://rocker.sch.bme.hu
-
- 1.4) What's the copyright on PostgreSQL?
-
- PostgreSQL is subject to the following COPYRIGHT.
-
- PostgreSQL Data Base Management System
-
- 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.
-
- 1.5) Support for PostgreSQL
-
- There is no official support for PostgreSQL from the original
- maintainers or from University of California, Berkeley. It is
- maintained through volunteer effort only.
-
- The main mailing list is: questions@postgreSQL.org. It is available
- for discussion o f matters pertaining to PostgreSQL, including but not
- limited to bug reports and fixes. For info on how to subscribe, send a
- mail with the lines in the body (not the subject line)
+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 being 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 current and future
+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.
+
+1.2) What does PostgreSQL run on?
+
+The authors have compiled and tested PostgreSQL on the following
+platforms(some of these compiles require gcc 2.7.0):
+
+ * aix - IBM on AIX 3.2.5 or 4.x
+ * alpha - DEC Alpha AXP on Digital Unix 2.0, 3.2, 4.0
+ * BSD44_derived - OSs derived from 4.4-lite BSD (NetBSD, FreeBSD)
+ * bsdi - BSD/OS 2.0, 2.01, 2.1, 3.0
+ * dgux - DG/UX 5.4R4.11
+ * hpux - HP PA-RISC on HP-UX 9.0, 10
+ * i386_solaris - i386 Solaris
+ * irix5 - SGI MIPS on IRIX 5.3
+ * linux - Intel x86 on Linux 2.0 and Linux ELF SPARC on Linux ELF PPC on
+ Linux Elf (For non-ELF Linux, see LINUX_ELF below).
+ * sco - SCO 3.2v5
+ * sparc_solaris - SUN SPARC on Solaris 2.4, 2.5, 2.5.1
+ * sunos4 - SUN SPARC on SunOS 4.1.3
+ * svr4 - Intel x86 on Intel SVR4 and MIPS
+ * ultrix4 - DEC MIPS on Ultrix 4.4
+
+The following platforms have known problems/bugs:
+
+ * nextstep - Motorola MC68K or Intel x86 on NeXTSTEP 3.2
+
+1.3) Where can I get PostgreSQL?
+
+The primary anonymous ftp site for PostgreSQL is:
+
+ * ftp://ftp.postgreSQL.org/pub
+
+A mirror site exists at:
+
+ * ftp://postgres95.vnet.net/pub/postgres95
+ * ftp://ftp.luga.or.at/pub/postgres95
+ * ftp://cal011111.student.utwente.nl/pub/postgres95
+ * ftp://ftp.uni-trier.de/pub/database/rdbms/postgres/postgres95
+ * ftp://rocker.sch.bme.hu
+
+1.4) What's the copyright on PostgreSQL?
+
+PostgreSQL is subject to the following COPYRIGHT.
+
+PostgreSQL Data Base Management System
+
+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.
+
+1.5) Support for PostgreSQL
+
+There is no official support for PostgreSQL from the original maintainers or
+from University of California, Berkeley. It is maintained through volunteer
+effort only.
+
+The main mailing list is: questions@postgreSQL.org. It is available for
+discussion o f matters pertaining to PostgreSQL, including but not limited
+to bug reports and fixes. For info on how to subscribe, send a mail with the
+lines in the body (not the subject line)
subscribe
end
- to questions-request@postgreSQL.org.
-
- There is also a digest list available. To subscribe to this list, send
- email to: questions-digest-request@postgreSQL.org with a BODY of:
+to questions-request@postgreSQL.org.
+There is also a digest list available. To subscribe to this list, send email
+to: questions-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.
-
- There is a bugs mailing list available. To subscribe to this list,
- send email to bugs-request@postgreSQL.org with a BODY of:
-
- There is also a developers discussion mailing list available. To
- subscribe to this list, send email to hackers-request@postgreSQL.org
- with a BODY of:
-
+Digests are sent out to members of this list whenever the main list has
+received around 30k of messages.
+
+There is a bugs mailing list available. To subscribe to this list, send
+email to bugs-request@postgreSQL.org with a BODY of:
+
+There is also a developers discussion mailing list available. To subscribe
+to this list, send email to hackers-request@postgreSQL.org with a BODY of:
subscribe
end
- Additional information about PostgreSQL can be found via the
- PostgreSQL WWW home page at:
-
+Additional information about PostgreSQL can be found via the PostgreSQL WWW
+home page at:
+
http://postgreSQL.org
-
- 1.6) Latest release of PostgreSQL
-
- The latest release of PostgreSQL is version 6.2.1, which was released
- on October 17th, 1997. We are testing 6.3 beta. For information about
- what is new in 6.3, see our TODO list on our WWW page.
-
- We plan to have major releases every three months.
-
- 1.7) Is there a commercial version of PostgreSQL?
-
- Illustra Information Technology (a wholly owned subsidiary of Informix
- Software, Inc.) sells an object-relational DBMS called Illustra that
- was originally based on postgres. Illustra has cosmetic similarities
- to PostgreSQL but has more features, is more robust, performs better,
- and offers real documentation and support. On the flip side, it costs
- money. For more information, contact sales@illustra.com
-
- 1.8) What documentation is available for PostgreSQL?
-
- A user manual, manual pages, and some small test examples are included
- in the distribution. The sql and built-in manual pages are
- particularly important.
-
- The www page contains pointers to an implementation guide and five
- papers written about postgres design concepts and features.
-
- 1.9) What version of SQL does PostgreSQL use?
-
- PostgreSQL supports a subset of SQL-92. It has most of the important
- constructs but lacks some of the functionality. The most visible
- differences are:
- * no support for nested subqueries
- * no HAVING clause under a GROUP BY
-
- On the other hand, you get to create user-defined types, functions,
- inheritance etc. If you're willing to help with PostgreSQL coding,
- eventually we can also add the missing features listed above.
-
- 1.10) Does PostgreSQL work with databases from earlier versions of postgres?
-
- PostgreSQL v1.09 is compatible with databases created with v1.01.
-
- Upgrading to 6.3 from earlier releases requires a dump and restore.
-
- Upgrading to 6.2.1 from pre-6.2 requires a dump and restore.
-
- Upgrading to 6.2.1 from 6.2 does not require a dump, but see the
- appropriate /migration file in the distribution.
-
- Those ugrading from versions earlier than 1.09 must upgrade to 1.09
- first without a dump/reload, then dump the data from 1.09, and then
- load it into 6.2.1 or 6.3 beta.
-
- 1.11) Are there ODBC drivers for PostgreSQL?
-
- There are two ODBC drivers available, PostODBC and OpenLink ODBC.
-
- For all people being interested in PostODBC, there are now two mailing
- lists devoted to the discussion of PostODBC. The mailing lists are:
- * postodbc-users@listserv.direct. net
- * postodbc-developers@listse rv.direct.net
-
- these lists are ordinary majordomo mailing lists. You can subscribe by
- sending a mail to:
- * majordomo@listserv.direct.net
-
- OpenLink ODBC is very popular. You can get it from
- http://www.openlinksw.com/postgres.html. It works with our standard
- ODBC client software so you'll have Postgres ODBC available on every
- client platform we support (Win, Mac, Unix, VMS).
-
- We 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.
-
- 1.12) What tools are available for hooking postgres to Web pages?
-
- A nice introduction to Database-backed Web pages can be seen at:
- http://www.webtools.com
-
- For web integration, PHP is an excellent interface. The URL for that
- is http://php.iquest.net
-
- PHP is great for simple stuff, but for more complex stuff, some still
- use the perl interface and CGI.pm.
-
- An WWW gatway based on WDB using perl can be downloaded from:
- * http://www.eol.ists.ca/~dunlop/wdb -p95
-
- 1.13) Does PostgreSQL have a graphical user interface? A report generator? A
- embedded query language interface?
-
- No. No. No. Not in the official distribution at least. Some users have
- reported some success at using 'pgbrowse' and 'onyx' as frontends to
- PostgreSQL. Several contributions are working on tk based frontend
- tools. Ask on the mailing list.
-
- 1.14) What is a good book to learn SQL?
-
- Many of our users like The Practical SQL Handbook, Bowman et al,
- Addison Wesley.
- _________________________________________________________________
-
+
+1.6) Latest release of PostgreSQL
+
+The latest release of PostgreSQL is version 6.2.1, which was released on
+October 17th, 1997. We are testing 6.3 beta. For information about what is
+new in 6.3, see our TODO list on our WWW page.
+
+We plan to have major releases every three months.
+
+1.7) Is there a commercial version of PostgreSQL?
+
+Illustra Information Technology (a wholly owned subsidiary of Informix
+Software, Inc.) sells an object-relational DBMS called Illustra that was
+originally based on postgres. Illustra has cosmetic similarities to
+PostgreSQL but has more features, is more robust, performs better, and
+offers real documentation and support. On the flip side, it costs money. For
+more information, contact sales@illustra.com
+
+1.8) What documentation is available for PostgreSQL?
+
+A user manual, manual pages, and some small test examples are included in
+the distribution. The sql and built-in manual pages are particularly
+important.
+
+The www page contains pointers to an implementation guide and five papers
+written about postgres design concepts and features.
+
+1.9) What version of SQL does PostgreSQL use?
+
+PostgreSQL supports a subset of SQL-92. It has most of the important
+constructs but lacks some of the functionality. The most visible differences
+are:
+
+ * no support for nested subqueries
+ * no HAVING clause under a GROUP BY
+
+On the other hand, you get to create user-defined types, functions,
+inheritance etc. If you're willing to help with PostgreSQL coding,
+eventually we can also add the missing features listed above.
+
+1.10) Does PostgreSQL work with databases from earlier versions of postgres?
+
+PostgreSQL v1.09 is compatible with databases created with v1.01.
+
+Upgrading to 6.3 from earlier releases requires a dump and restore.
+
+Upgrading to 6.2.1 from pre-6.2 requires a dump and restore.
+
+Upgrading to 6.2.1 from 6.2 does not require a dump, but see the appropriate
+/migration file in the distribution.
+
+Those ugrading from versions earlier than 1.09 must upgrade to 1.09 first
+without a dump/reload, then dump the data from 1.09, and then load it into
+6.2.1 or 6.3 beta.
+
+1.11) Are there ODBC drivers for PostgreSQL?
+
+There are two ODBC drivers available, PostODBC and OpenLink ODBC.
+
+For all people being interested in PostODBC, there are now two mailing lists
+devoted to the discussion of PostODBC. The mailing lists are:
+
+ * postodbc-users@listserv.direct. net
+ * postodbc-developers@listse rv.direct.net
+
+these lists are ordinary majordomo mailing lists. You can subscribe by
+sending a mail to:
+
+ * majordomo@listserv.direct.net
+
+OpenLink ODBC is very popular. You can get it from
+http://www.openlinksw.com/postgres.html. It works with our standard ODBC
+client software so you'll have Postgres ODBC available on every client
+platform we support (Win, Mac, Unix, VMS).
+
+We 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.
+
+1.12) What tools are available for hooking postgres to Web pages?
+
+A nice introduction to Database-backed Web pages can be seen at:
+http://www.webtools.com
+
+For web integration, PHP is an excellent interface. The URL for that is
+http://php.iquest.net
+
+PHP is great for simple stuff, but for more complex stuff, some still use
+the perl interface and CGI.pm.
+
+An WWW gatway based on WDB using perl can be downloaded from:
+
+ * http://www.eol.ists.ca/~dunlop/wdb -p95
+
+1.13) Does PostgreSQL have a graphical user interface? A report generator? A
+embedded query language interface?
+
+No. No. No. Not in the official distribution at least. Some users have
+reported some success at using 'pgbrowse' and 'onyx' as frontends to
+PostgreSQL. Several contributions are working on tk based frontend tools.
+Ask on the mailing list.
+
+1.14) What is a good book to learn SQL?
+
+Many of our users like The Practical SQL Handbook, Bowman et al, Addison
+Wesley.
+
+ ------------------------------------------------------------------------
+
Section 2: Installation Questions
- 2.1) initdb doesn't run
-
- * check to see that you have the proper paths set
- * check that the 'postgres' user owns all the right files
- * ensure that there are files in $PGDATA/files, and that they are
- non-empty. If they aren't, then "gmake install" failed for some
- reason
-
- 2.2) when I start up the postmaster, I get "FindBackend: could not find a
- backend to execute..." "postmaster: could not find backend to execute..."
-
- You probably do not have the right path set up. The 'postgres'
- executable needs to be in your path.
-
- 2.3) The system seems to be confused about commas, decimal points, and date
- formats.
-
- Check your locale configuration. PostgreSQL uses the locale settings
- of the user that ran the postmaster process. Set those accordingly for
- your operating environment.
-
- 2.4) How do I install PostgreSQL somewhere other than /usr/local/pgsql?
-
- You need to edit Makefile.global and change POSTGRESDIR accordingly,
- or create a Makefile.custom and define POSTGRESDIR there.
-
- 2.5) When I run postmaster, I get a Bad System Call core dumped message.
-
- It could be a variety of problems, but first check to see that you
- have system V extensions installed on your kernel. PostgreSQL requires
- kernel support for shared memory.
-
- 2.6) When I try to start the postmaster, I get IpcMemoryCreate errors.
-
- You either do not have shared memory configured properly in 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 you configure postmaster to run with. For most systems, with
- default buffer sizes, you need a minimum of ~760K.
-
- 2.7) I have changed a source file, but a recompile does 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'.
-
- 2.8) How do I prevent other hosts from accessing my PostgreSQL backend?
-
- Use host-based authentication by modifying the file $PGDATA/pg_hba
- accordingly.
-
- 2.9) I can't access the database as the 'root' user.
-
- 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 any user to dynamically link object modules
- into the database engine.
-
- 2.10) All my servers crash under concurrent table access. Why?
-
- This problem can be caused by a kernel that is not configured to
- support semaphores.
-
- 2.11) How do I tune the database engine for better performance?
-
- There are two things that can be done. You can use Openlink's option
- to 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 shared among the backend processes. If you make
- this parameter too high, the process will not start or crash
- unexpectedly. Each buffer is 8K and the defualt is 64 buffers.
-
- You can also use the postgres -S option to increase the maximum amount
- of memory used by each backend process for temporary sorts. Each
- buffer is 1K and the defualt is 512 buffers.
-
- 2.12) What debugging features are available in PostgreSQL?
-
- 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:
+2.1) initdb doesn't run
+
+ * check to see that you have the proper paths set
+ * check that the 'postgres' user owns all the right files
+ * ensure that there are files in $PGDATA/files, and that they are
+ non-empty. If they aren't, then "gmake install" failed for some reason
+
+2.2) when I start up the postmaster, I get "FindBackend: could not find a
+backend to execute..." "postmaster: could not find backend to execute..."
+
+You probably do not have the right path set up. The 'postgres' executable
+needs to be in your path.
+2.3) The system seems to be confused about commas, decimal points, and date
+formats.
+
+Check your locale configuration. PostgreSQL uses the locale settings of the
+user that ran the postmaster process. Set those accordingly for your
+operating environment.
+
+2.4) How do I install PostgreSQL somewhere other than /usr/local/pgsql?
+
+You need to edit Makefile.global and change POSTGRESDIR accordingly, or
+create a Makefile.custom and define POSTGRESDIR there.
+
+2.5) When I run postmaster, I get a Bad System Call core dumped message.
+
+It could be a variety of problems, but first check to see that you have
+system V extensions installed on your kernel. PostgreSQL requires kernel
+support for shared memory.
+
+2.6) When I try to start the postmaster, I get IpcMemoryCreate errors.
+
+You either do not have shared memory configured properly in 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 you configure
+postmaster to run with. For most systems, with default buffer sizes, you
+need a minimum of ~760K.
+
+2.7) I have changed a source file, but a recompile does 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'.
+
+2.8) How do I prevent other hosts from accessing my PostgreSQL backend?
+
+Use host-based authentication by modifying the file $PGDATA/pg_hba
+accordingly.
+
+2.9) I can't access the database as the 'root' user.
+
+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 any user to dynamically link object modules into the database
+engine.
+
+2.10) All my servers crash under concurrent table access. Why?
+
+This problem can be caused by a kernel that is not configured to support
+semaphores.
+
+2.11) How do I tune the database engine for better performance?
+
+There are two things that can be done. You can use Openlink's option to
+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 shared among the backend processes. If you make this
+parameter too high, the process will not start or crash unexpectedly. Each
+buffer is 8K and the defualt is 64 buffers.
+
+You can also use the postgres -S option to increase the maximum amount of
+memory used by each backend process for temporary sorts. Each buffer is 1K
+and the defualt is 512 buffers.
+
+2.12) What debugging features are available in PostgreSQL?
+
+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 can contain 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
- 1-3 that specifies the debug level. Be warned that a debug level of 3
- generates large log files.
-
- You can actuall 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. Some
- operating system can attach to a running backend directly to diagnose
- problems.
-
- The postgres program has a -s, -A, -t options that can be very usefull
- 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 current directory.
-
- The EXPLAIN command (see this FAQ) allows you to see how PostgreSQL is
- interpreting your query.
-
- 2.13) How do I enable more than 32 concurrent backends?
-
- Edit include/storage/sinvaladt.h, and change the value of
- MaxBackendId. In the future, we plan to make this a configurable
- prameter.
- _________________________________________________________________
-
+This will put a server.log file in the top-level PostgreSQL directory. This
+file can contain 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 1-3 that specifies
+the debug level. Be warned that a debug level of 3 generates large log
+files.
+
+You can actuall 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. Some operating system can attach to a
+running backend directly to diagnose problems.
+
+The postgres program has a -s, -A, -t options that can be very usefull 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
+current directory.
+
+The EXPLAIN command (see this FAQ) allows you to see how PostgreSQL is
+interpreting your query.
+
+2.13) How do I enable more than 32 concurrent backends?
+
+Edit include/storage/sinvaladt.h, and change the value of MaxBackendId. In
+the future, we plan to make this a configurable prameter.
+
+ ------------------------------------------------------------------------
+
Section 3: PostgreSQL Features
- 3.1) Does PostgreSQL support nested subqueries?
-
- Subqueries are not implemented, but they can be simulated using sql
- functions.
-
- 3.2) I've having a lot of problems using rules.
-
- Currently, the rule system in PostgreSQL is mostly broken. It works
- enough to support the view mechanism, but that's about it. Use
- PostgreSQL rules at your own peril.
-
- 3.3) I can't seem to write into the middle of large objects reliably.
-
- The Inversion large object system in PostgreSQL is also mostly broken.
- It works well enough for storing large wads of data and reading them
- back out, but the implementation has some underlying problems. Use
- PostgreSQL large objects at your own peril.
-
- 3.4) How can I write client applications to PostgreSQL?
-
- PostgreSQL supports a C-callable library interface called libpq as
- well as many others. See the /src/interfaces directory.
-
- Others have contributed a perl interface and a WWW gateway to
- PostgreSQL. See the PostgreSQL home pages for more details.
-
- 3.5) How do I set up a pg_group?
-
- Currently, there is no easy interface to set up user groups. You have
- to explicitly insert/update the pg_group table. For example:
+3.1) Does PostgreSQL support nested subqueries?
+
+Subqueries are not implemented, but they can be simulated using sql
+functions.
+
+3.2) I've having a lot of problems using rules.
+
+Currently, the rule system in PostgreSQL is mostly broken. It works enough
+to support the view mechanism, but that's about it. Use PostgreSQL rules at
+your own peril.
+
+3.3) I can't seem to write into the middle of large objects reliably.
+
+The Inversion large object system in PostgreSQL is also mostly broken. It
+works well enough for storing large wads of data and reading them back out,
+but the implementation has some underlying problems. Use PostgreSQL large
+objects at your own peril.
+
+3.4) How can I write client applications to PostgreSQL?
+PostgreSQL supports a C-callable library interface called libpq as well as
+many others. See the /src/interfaces directory.
+
+Others have contributed a perl interface and a WWW gateway to PostgreSQL.
+See the PostgreSQL home pages for more details.
+
+3.5) How do I set up a pg_group?
+
+Currently, there is no easy interface to set up user groups. You have to
+explicitly insert/update the pg_group table. For example:
jolly=> insert into pg_group (groname, grosysid, grolist)
jolly=> values ('posthackers', '1234', '{5443, 8261}');
CHANGE
jolly=>
- The fields in pg_group are:
- * groname: the group name. This a char16 and should be purely
- alphanumeric. Do not include underscores or other punctuation.
- * grosysid: the group id. This is an int4. This should be unique for
- each group.
- * grolist: the list of pg_user id's that belong in the group. This
- is an int4[].
-
- 3.6) What is the exact difference between binary cursors and normal cursors?
-
- See the declare manual page for a description.
-
- 3.7) What is a R-tree index and what is it used for?
-
- 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 a R-tree index can be built on an attribute of type
- 'point', the system can more efficient answer queries like 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"
-
- Builtin 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 require a bit of work and we don't currently have
- any documentation on how to do it.
-
- 3.8) What is the maximum size for a tuple?
-
- Tuples are limited to 8K bytes. Taking into account system attributes
- and other overhead, one should stay well shy of 8,000 bytes to be on
- the safe side. To use attributes larger than 8K, try using the large
- objects interface.
-
- Tuples do not cross 8k boundaries so a 5k tuple will require 8k of
- storage.
-
- 3.9) I defined indices but my queries don't seem to make use of them. Why?
-
- PostgreSQL does not automatically maintain statistics. One has to make
- an explicit 'vacuum' call to update the statistics. After statistics
- are updated, the optimizer has a better shot at using indices. Note
- that the optimizer is limited and does not use indices in some
- circumstances (such as OR clauses). For column-specific optimization
- statistics, use 'vacuum analyze'.
-
- If the system still does not see the index, it is probably because you
- have created an index on a field with the improper *_ops type. For
- example, you have created a CHAR(4) field, but have specified a
- char_ops index type_class.
-
- See the create_index manual page for information on what type classes
- are available. It must match the field type.
-
- Postgres does not warn the user when the improper index is created.
-
- Indexes not used for ORDER BY operations.
-
- 3.10) How do I do regular expression searches? case-insensitive regexp
- searching?
-
- See the pgbuiltin manual page. Search for regular expression.
-
- 3.11) I experienced a server crash during a vacuum. How do I remove the lock
- file?
-
- See the vacuum manual page.
-
- 3.12) What is the difference between the various character types?
-
+The fields in pg_group are:
+
+ * groname: the group name. This a char16 and should be purely
+ alphanumeric. Do not include underscores or other punctuation.
+ * grosysid: the group id. This is an int4. This should be unique for each
+ group.
+ * grolist: the list of pg_user id's that belong in the group. This is an
+ int4[].
+
+3.6) What is the exact difference between binary cursors and normal cursors?
+
+See the declare manual page for a description.
+
+3.7) What is a R-tree index and what is it used for?
+
+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 a
+R-tree index can be built on an attribute of type 'point', the system can
+more efficient answer queries like 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"
+
+Builtin 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 require a bit of work and we don't currently have any documentation
+on how to do it.
+
+3.8) What is the maximum size for a tuple?
+
+Tuples are limited to 8K bytes. Taking into account system attributes and
+other overhead, one should stay well shy of 8,000 bytes to be on the safe
+side. To use attributes larger than 8K, try using the large objects
+interface.
+
+Tuples do not cross 8k boundaries so a 5k tuple will require 8k of storage.
+
+3.9) I defined indices but my queries don't seem to make use of them. Why?
+
+PostgreSQL does not automatically maintain statistics. One has to make an
+explicit 'vacuum' call to update the statistics. After statistics are
+updated, the optimizer has a better shot at using indices. Note that the
+optimizer is limited and does not use indices in some circumstances (such as
+OR clauses). For column-specific optimization statistics, use 'vacuum
+analyze'.
+
+If the system still does not see the index, it is probably because you have
+created an index on a field with the improper *_ops type. For example, you
+have created a CHAR(4) field, but have specified a char_ops index
+type_class.
+
+See the create_index manual page for information on what type classes are
+available. It must match the field type.
+
+Postgres does not warn the user when the improper index is created.
+
+Indexes not used for ORDER BY operations.
+
+3.10) How do I do regular expression searches? case-insensitive regexp
+searching?
+
+See the pgbuiltin manual page. Search for regular expression.
+
+3.11) I experienced a server crash during a vacuum. How do I remove the lock
+file?
+
+See the vacuum manual page.
+
+3.12) What is the difference between the various character types?
+
Type Internal Name Notes
--------------------------------------------------
CHAR char 1 character }
TEXT text length limited only by maximum tuple length
BYTEA bytea variable-length array of bytes
- Remember, you need to use the internal name when creating indexes on
- these fields or when doing other internal operations.
-
- The last four types above are "varlena" types (i.e. the first four
- bytes are the length, followed by the data). CHAR(#) allocates the
- maximum number of bytes no matter how much data is stored in the
- field. TEXT, VARCHAR(#), and BYTEA all have variable length on the
- disk.
-
- 3.13) In a query, how do I detect if a field is NULL?
-
- You test the column with IS NULL and IS NOT NULL.
-
- 3.14) How do I see how the query optimizer is evaluating my query?
-
- See the explain manual page.
-
- 3.15) How do I create a serial field?
-
- Postgres does not allow the user to specifiy a user column as type
- SERIAL. Instead, you can use each row's oid field as a unique value.
- However, if you need to dump and reload the database, you need to use
- pgdump's -o option or COPY's WITH OIDS option to preserver the oids.
-
- We also have a SEQUENCE function that is similar to SERIAL. See the
- create_sequence manual page.
-
- Another valid way of doing this is to create a function:
+You need to use the internal name when doing internal operations.
+
+The last four types above are "varlena" types (i.e. the first four bytes are
+the length, followed by the data). CHAR(#) allocates the maximum number of
+bytes no matter how much data is stored in the field. TEXT, VARCHAR(#), and
+BYTEA all have variable length on the disk, and because of this, there is a
+small performance penalty for using them. Specifically, the penalty is for
+access to any columns after the first column of this type.
+
+3.13) In a query, how do I detect if a field is NULL?
+
+You test the column with IS NULL and IS NOT NULL.
+
+3.14) How do I see how the query optimizer is evaluating my query?
+
+See the explain manual page.
+
+3.15) How do I create a serial field?
+
+Postgres does not allow the user to specifiy a user column as type SERIAL.
+Instead, you can use each row's oid field as a unique value. However, if you
+need to dump and reload the database, you need to use pgdump's -o option or
+COPY's WITH OIDS option to preserver the oids.
+
+We also have a SEQUENCE function that is similar to SERIAL. See the
+create_sequence manual page.
+
+Another valid way of doing this is to create a function:
create table my_oids (f1 int4);
insert into my_oids values (1);
'update my_oids set f1 = f1 + 1; select f1 from my_oids; '
language 'sql';
- then:
+then:
create table my_stuff (my_key int4, value text);
insert into my_stuff values (new_oid(), 'hello');
- However, keep in mind there is a race condition here where one server
- could do the update, then another one do an update, and they both
- could select the same new id. This statement should be performed
- within a transaction.
-
- Yet another way is to use general trigger function autoinc() from
- contrib/spi/autoinc.c.
-
- 3.16) What are the pg_psort.XXX files in my database directory?
-
- They are temporary sort files generated by the query executor. For
- example, if a sort needs to be done to satisfy an ORDER BY, some temp
- files are generated as a result of the sort.
-
- If you have no transactions or sorts running at the time, it is safe
- to delete the pg_psort.XXX files.
-
- 3.17) Why can't I connect to my database from another machine?
-
- The default configuration allows only connections from tcp/ip host
- localhost. You need to add a host entry to the file pgsql/data/pg_hba.
- See the hba_conf manual page.
-
- 3.18) How do I find out what indexes or operations are defined in the
- database?
-
- Run the file pgsql/src/tutorial/syscat.source. It illustrates many of
- the 'select's needed to get information out of the database system
- tables.
-
- 3.19) What is the time-warp feature and how does it relate to vacuum?
-
- PostgreSQL handles data changes differently than most database
- systems. When a row is changed in a table, the original row is marked
- with the time it was changed, and a new row is created with the
- current data. By default, only current rows are used in a table. If
- you specify a date/time after the table name in a FROM clause, you can
- access the data that was current at that time, i.e.
+However, keep in mind there is a race condition here where one server could
+do the update, then another one do an update, and they both could select the
+same new id. This statement should be performed within a transaction.
+Yet another way is to use general trigger function autoinc() from
+contrib/spi/autoinc.c.
+
+3.16) What are the pg_psort.XXX files in my database directory?
+
+They are temporary sort files generated by the query executor. For example,
+if a sort needs to be done to satisfy an ORDER BY, some temp files are
+generated as a result of the sort.
+
+If you have no transactions or sorts running at the time, it is safe to
+delete the pg_psort.XXX files.
+
+3.17) Why can't I connect to my database from another machine?
+
+The default configuration allows only connections from tcp/ip host
+localhost. You need to add a host entry to the file pgsql/data/pg_hba. See
+the hba_conf manual page.
+
+3.18) How do I find out what indexes or operations are defined in the
+database?
+
+Run the file pgsql/src/tutorial/syscat.source. It illustrates many of the
+'select's needed to get information out of the database system tables.
+
+3.19) What is the time-warp feature and how does it relate to vacuum?
+
+PostgreSQL handles data changes differently than most database systems. When
+a row is changed in a table, the original row is marked with the time it was
+changed, and a new row is created with the current data. By default, only
+current rows are used in a table. If you specify a date/time after the table
+name in a FROM clause, you can access the data that was current at that
+time, i.e.
SELECT *
FROM employees ['July 24, 1996 09:00:00']
- displays employee rows in the table at the specified time. You can
- specify intervals like [date,date], [date,], [,date], or [,]. This
- last option accesses all rows that ever existed.
-
- INSERTed rows get a timestamp too, so rows that were not in the table
- at the desired time will not appear.
-
- Vacuum removes rows that are no longer current. This time-warp feature
- is used by the engine for rollback and crash recovery. Expiration
- times can be set with purge.
-
- In 6.0, once a table is vacuumed, the creation time of a row may be
- incorrect, causing time-traval to fail.
-
- The time-travel feature will be removed in 6.3.
-
- 3.20) What is an oid? What is a tid?
-
- Oids are Postgres's answer to unique row ids or serial columns. Every
- row that is created in Postgres gets a unique oid. All oids generated
- by initdb are less than 16384 (from backend/access/transam.h). All
- post-initdb (user-created) oids are equal or greater that this. All
- these oids are unique not only within a table, or database, but unique
- within the entire postgres installation.
-
- Postgres uses oids in its internal system tables to link rows in
- separate 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. See the sql(l) manual page to see the other internal
- columns. You can create an index on the oid field for faster access.
-
- Tids are used to indentify 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. They can not be
- accessed through sql.
-
- 3.21) What is the meaning of some of the terms used in Postgres?
-
- Some of the source code and older documentation use terms that have
- more common usage. Here are some:
- * row, record, tuple
- * attribute, field, column
- * table, class
- * retrieve, select
- * replace, update
- * append, insert
- * oid, serial value
- * portal, cursor
- * range variable, table name, table alias
-
- Please let me know if you think of any more.
-
- 3.22) What is Genetic Query Optimization?
-
- The GEQO module in PostgreSQL is intended to solve the query
- optimization problem of joining many tables by means of a Genetic
- Algorithm (GA). It allows the handling of large join queries through
- non-exhaustive search.
-
- For further information see README.GEQO <utesch@aut.tu-freiberg.de>.
-
- 3.23) How do you remove a column from a table?
-
- We do not support ALTER TABLE DROP COLUMN, but do this:
+displays employee rows in the table at the specified time. You can specify
+intervals like [date,date], [date,], [,date], or [,]. This last option
+accesses all rows that ever existed.
+
+INSERTed rows get a timestamp too, so rows that were not in the table at the
+desired time will not appear.
+
+Vacuum removes rows that are no longer current. This time-warp feature is
+used by the engine for rollback and crash recovery. Expiration times can be
+set with purge.
+
+In 6.0, once a table is vacuumed, the creation time of a row may be
+incorrect, causing time-traval to fail.
+
+The time-travel feature will be removed in 6.3.
+
+3.20) What is an oid? What is a tid?
+
+Oids are Postgres's answer to unique row ids or serial columns. Every row
+that is created in Postgres gets a unique oid. All oids generated by initdb
+are less than 16384 (from backend/access/transam.h). All post-initdb
+(user-created) oids are equal or greater that this. All these oids are
+unique not only within a table, or database, but unique within the entire
+postgres installation.
+
+Postgres uses oids in its internal system tables to link rows in separate
+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. See
+the sql(l) manual page to see the other internal columns. You can create an
+index on the oid field for faster access.
+
+Tids are used to indentify 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. They can not be accessed through
+sql.
+
+3.21) What is the meaning of some of the terms used in Postgres?
+
+Some of the source code and older documentation use terms that have more
+common usage. Here are some:
+
+ * row, record, tuple
+ * attribute, field, column
+ * table, class
+ * retrieve, select
+ * replace, update
+ * append, insert
+ * oid, serial value
+ * portal, cursor
+ * range variable, table name, table alias
+
+Please let me know if you think of any more.
+
+3.22) What is Genetic Query Optimization?
+
+The GEQO module in PostgreSQL is intended to solve the query optimization
+problem of joining many tables by means of a Genetic Algorithm (GA). It
+allows the handling of large join queries through non-exhaustive search.
+
+For further information see README.GEQO <utesch@aut.tu-freiberg.de>.
+
+3.23) 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
DROP TABLE old_table;
ALTER TABLE new_table RENAME TO old_table;
- 3.24) How do SELECT only the first few rows of a query?
-
- See the fetch manual page.
-
- This only prevents all row results from being transfered to the
- client. The entire query must be evaluated, even if you only want just
- first few rows. Consider a query that has and ORDER BY. There is no
- way to return any rows until the entire query is evaluated and sorted.
-
- 3.25) Why can't I create a column named "time"?
-
- 6.2.1 has added some new restricted keywords as we make PostgreSQL
- more ANSI-92 compilant. The next release will have this restriction
- removed. There is a patch on ftp.postgresql.org that will allow this
- feature now.
-
- 3.26)How much database disk space is required to store data from a typical
- flat file?
-
- Consider a file with 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:
+3.24) How do SELECT only the first few rows of a query?
+
+See the fetch manual page.
+
+This only prevents all row results from being transfered to the client. The
+entire query must be evaluated, even if you only want just first few rows.
+Consider a query that has and ORDER BY. There is no way to return any rows
+until the entire query is evaluated and sorted.
+
+3.25) Why can't I create a column named "time"?
+
+6.2.1 has added some new restricted keywords as we make PostgreSQL more
+ANSI-92 compilant. The next release will have this restriction removed.
+There is a patch on ftp.postgresql.org that will allow this feature now.
+
+3.26)How much database disk space is required to store data from a typical
+flat file?
+
+Consider a file with 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:
40 bytes + each row header (approximate)
8 bytes + two int fields @ 4 bytes each
Indexes do not contain as much overhead, but do contain the data that
is being indexed, so they can be large also.
- _________________________________________________________________
-
+
+ ------------------------------------------------------------------------
+
Section 4: Extending PostgreSQL
- 4.1) I wrote a user-defined function and when I run it in psql, it dumps
- core.
-
- The problem could be a number of things. Try testing your user-defined
- function in a stand alone test program first. Also, make sure you are
- not sending elog NOTICES when the front-end is expecting data, such as
- during a type_in() or type_out() functions
-
- 4.2) I get messages of the type NOTICE:PortalHeapMemoryFree: 0x402251d0 not
- in alloc set!
-
- You are pfree'ing something that was not palloc'ed. When writing
- user-defined functions, do not include the file "libpq-fe.h". Doing so
- will cause your palloc to be a malloc instead of a free. Then, when
- the backend pfrees the storage, you get the notice message.
-
- 4.3) I've written some nifty new types and functions for PostgreSQL.
-
- Please share them with other PostgreSQL users. Send your extensions to
- mailing list, and they will eventually end up in the contrib/
- subdirectory.
-
- 4.4) How do I write a C function to return a tuple?
-
- This requires extreme wizardry, so extreme that the authors have not
- ever tried it, though in principle it can be done. The short answer is
- ... you can't. This capability is forthcoming in the future.
- _________________________________________________________________
-
+4.1) I wrote a user-defined function and when I run it in psql, it dumps
+core.
+
+The problem could be a number of things. Try testing your user-defined
+function in a stand alone test program first. Also, make sure you are not
+sending elog NOTICES when the front-end is expecting data, such as during a
+type_in() or type_out() functions
+
+4.2) I get messages of the type NOTICE:PortalHeapMemoryFree: 0x402251d0 not
+in alloc set!
+
+You are pfree'ing something that was not palloc'ed. When writing
+user-defined functions, do not include the file "libpq-fe.h". Doing so will
+cause your palloc to be a malloc instead of a free. Then, when the backend
+pfrees the storage, you get the notice message.
+
+4.3) I've written some nifty new types and functions for PostgreSQL.
+
+Please share them with other PostgreSQL users. Send your extensions to
+mailing list, and they will eventually end up in the contrib/ subdirectory.
+
+4.4) How do I write a C function to return a tuple?
+
+This requires extreme wizardry, so extreme that the authors have not ever
+tried it, though in principle it can be done. The short answer is ... you
+can't. This capability is forthcoming in the future.
+
+ ------------------------------------------------------------------------
+
Section 5: Bugs
- 5.1) How do I make a bug report?
-
- Check the current FAQ at http://postgreSQL.org
-
- Also check out our ftp site ftp://ftp.postgreSQL.org/pub to see if
- there is a more recent PostgreSQL version.
-
- You can also fill out the "bug-template" file and send it to:
- * bugs@postgreSQL.org
-
- This is the address of the developers mailing list.
+5.1) How do I make a bug report?
+
+Check the current FAQ at http://postgreSQL.org
+
+Also check out our ftp site ftp://ftp.postgreSQL.org/pub to see if there is
+a more recent PostgreSQL version.
+
+You can also fill out the "bug-template" file and send it to:
+
+ * bugs@postgreSQL.org
+
+This is the address of the developers mailing list.
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