+++ /dev/null
-<HTML>
-<HEAD>
-<TITLE>PostgreSQL FAQ</TITLE>
-</HEAD>
-<BODY BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#FF0000" VLINK="#A00000" ALINK="#0000FF">
-<H1>
-Frequently Asked Questions (FAQ) for PostgreSQL
-</H1>
-<P>
-Last updated: Fri Jun 2 11:32:13 EDT 2000
-<P>
-Current maintainer: Bruce Momjian (<A
-HREF="mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR><P>
-
-The most recent version of this document can be viewed at the postgreSQL
-Web site, <A HREF="http://www.Postgresql.org">http://www.PostgreSQL.org</A>.<P>
-
-Linux-specific questions are answered in <A
-HREF="http://www.PostgreSQL.org/docs/faq-linux.html">http://www.PostgreSQL.org/docs/faq-linux.html</A>.<P>
-
-HPUX-specific questions are answered in <A
-HREF="http://www.PostgreSQL.org/docs/faq-hpux.html">http://www.PostgreSQL.org/docs/faq-hpux.html</A>.<P>
-
-Solaris-specific questions are answered in <A
-HREF="http://www.postgresql.org/docs/faq-solaris.html">http://www.postgresql.org/docs/faq-solaris.html</A>.<P>
-
-Irix-specific questions are answered in <A
-HREF="http://www.PostgreSQL.org/docs/faq-irix.html">http://www.PostgreSQL.org/docs/faq-irix.html</A>.<P>
-
-<HR><P>
-
-<H2><CENTER>General Questions</CENTER></H2>
-
-<A HREF="#1.1">1.1</A>) What is PostgreSQL?<BR>
-<A HREF="#1.2">1.2</A>) What's the copyright on PostgreSQL?<BR>
-<A HREF="#1.3">1.3</A>) What Unix platforms does PostgreSQL run on?<BR>
-<A HREF="#1.4">1.4</A>) What non-unix ports are available?<BR>
-<A HREF="#1.5">1.5</A>) Where can I get PostgreSQL?<BR>
-<A HREF="#1.6">1.6</A>) Where can I get support for PostgreSQL?<BR>
-<A HREF="#1.7">1.7</A>) What is the latest release of PostgreSQL?<BR>
-<A HREF="#1.8">1.8</A>) What documentation is available for PostgreSQL?<BR>
-<A HREF="#1.9">1.9</A>) How do I find out about known bugs or missing features?<BR>
-<A HREF="#1.10">1.10</A>) How can I learn SQL?<BR>
-<A HREF="#1.11">1.11</A>) Is PostgreSQL Y2K compliant?<BR>
-<A HREF="#1.12">1.12</A>) How do I join the development team?<BR>
-<A HREF="#1.13">1.13</A>) How do I submit a bug report?<BR>
-<A HREF="#1.14">1.14</A>) How does PostgreSQL compare to other DBMS's?<BR>
-
-
-<H2><CENTER>User Client Questions</CENTER></H2>
-
-<A HREF="#2.1">2.1</A>) Are there ODBC drivers for
-PostgreSQL?<BR>
-<A HREF="#2.2">2.2</A>) What tools are available for hooking
-PostgreSQL to Web pages?<BR>
-<A HREF="#2.3">2.3</A>) Does PostgreSQL have a graphical user interface?
-A report generator? An embedded query language interface?<BR>
-<A HREF="#2.4">2.4</A>) What languages are available to communicate
-with PostgreSQL?<BR>
-
-
-<H2><CENTER>Administrative Questions</CENTER></H2>
-
-<A HREF="#3.1">3.1</A>) Why does initdb fail?<BR>
-<A HREF="#3.2">3.2</A>) How do I install PostgreSQL somewhere other than
-/usr/local/pgsql?<BR>
-<A HREF="#3.3">3.3</A>) When I start the postmaster, I get a
-<I>Bad System Call</I> or core dumped message. Why?<BR>
-<A HREF="#3.4">3.4</A>) When I try to start the postmaster, I get
-<I>IpcMemoryCreate</I> errors3. Why?<BR>
-<A HREF="#3.5">3.5</A>) When I try to start the postmaster, I get
-<I>IpcSemaphoreCreate</I> errors. Why?<BR>
-<A HREF="#3.6">3.6</A>) How do I prevent other hosts from accessing my
-PostgreSQL database?<BR>
-<A HREF="#3.7">3.7</A>) Why can't I connect to my database from
-another machine?<BR>
-<A HREF="#3.8">3.8</A>) Why can't I access the database as the
-<I>root</I> user?<BR>
-<A HREF="#3.9">3.9</A>) All my servers crash under concurrent
-table access. Why?<BR>
-<A HREF="#3.10">3.10</A>) How do I tune the database engine for
-better performance?<BR>
-<A HREF="#3.11">3.11</A>) What debugging features are available in
-PostgreSQL?<BR>
-<A HREF="#3.12">3.12</A>) I get 'Sorry, too many clients' when trying to
-connect. Why?<BR>
-<A HREF="#3.13">3.13</A>) What are the pg_psort.XXX files in my
-database directory?<BR>
-
-<H2><CENTER>Operational Questions</CENTER></H2>
-
-<A HREF="#4.1">4.1</A>) The system seems to be confused about commas,
-decimal points, and date formats.<BR>
-<A HREF="#4.2">4.2</A>) What is the exact difference between
-binary cursors and normal cursors?<BR>
-<A HREF="#4.3">4.3</A>) How do I <I>select</I> only the first few rows of
-a query?<BR>
-
-<A HREF="#4.4">4.4</A>) How do I get a list of tables, or other
-things I can see in <I>psql?</I><BR>
-<A HREF="#4.5">4.5</A>) How do you remove a column from a table?<BR>
-
-<A HREF="#4.6">4.6</A>) What is the maximum size for a
-row, table, database?<BR>
-<A HREF="#4.7">4.7</A>) How much database disk space is required
-to store data from a typical flat file?<BR>
-
-<A HREF="#4.8">4.8</A>) How do I find out what indices or
-operations are defined in the database?<BR>
-<A HREF="#4.9">4.9</A>) My queries are slow or don't make use of the
-indexes. Why?<BR>
-<A HREF="#4.10">4.10</A>) How do I see how the query optimizer is
-evaluating my query?<BR>
-<A HREF="#4.11">4.11</A>) What is an R-tree index?<BR>
-<A HREF="#4.12">4.12</A>) What is Genetic Query Optimization?<BR>
-
-<A HREF="#4.13">4.13</A>) How do I do regular expression searches
-and case-insensitive regexp searching?<BR>
-<A HREF="#4.14">4.14</A>) In a query, how do I detect if a field
-is NULL?<BR>
-<A HREF="#4.15">4.15</A>) What is the difference between the
-various character types?<BR>
-<A HREF="#4.16.1">4.16.1</A>) How do I create a serial/auto-incrementing field?<BR>
-<A HREF="#4.16.2">4.16.2</A>) How do I get the value of a serial insert?<BR>
-<A HREF="#4.16.3">4.16.3</A>) Don't currval() and nextval() lead to a
-race condition with other concurrent backend processes?<BR>
-
-<A HREF="#4.17">4.17</A>) What is an oid? What is a tid?<BR>
-<A HREF="#4.18">4.18</A>) What is the meaning of some of the terms
-used in PostgreSQL?<BR>
-
-<A HREF="#4.19">4.19</A>) Why do I get the error "FATAL: palloc
-failure: memory exhausted?"<BR>
-<A HREF="#4.20">4.20</A>) How do I tell what PostgreSQL version I
-am running? <BR>
-<A HREF="#4.21">4.21</A>) My large-object operations get <I>invalid
-large obj descriptor.</I> Why?<BR>
-<A HREF="#4.22">4.22</A>) How do I create a column that will default to the
-current time?<BR>
-<A HREF="#4.23">4.23</A>) Why are my subqueries using <CODE>IN</CODE> so
-slow?<BR>
-<A HREF="#4.24">4.24</A>) How do I do an <i>outer</i> join?<BR>
-
-<H2><CENTER>Extending PostgreSQL</CENTER></H2>
-
-<A HREF="#5.1">5.1</A>) I wrote a user-defined function. When I run
-it in <I>psql,</I> why does it dump core?<BR>
-<A HREF="#5.2">5.2</A>) What does the message:
-<I>NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!</I> mean?<BR>
-<A HREF="#5.3">5.3</A>) How can I contribute some nifty new types and functions
-for PostgreSQL?<BR>
-<A HREF="#5.4">5.4</A>) How do I write a C function to return a
-tuple?<BR>
-<A HREF="#5.5">5.5</A>) I have changed a source file. Why does the
-recompile does not see the change?<BR>
-
-
-<HR>
-
-<H2><CENTER>General Questions</CENTER></H2>
-<H4><A
-NAME="1.1">1.1</A>) What is PostgreSQL?</H4><P>
-
-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.<P>
-
-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 (<A
-HREF="mailto:scrappy@postgreSQL.org">scrappy@postgreSQL.org</A>). (See
-below on how to join). This team is now responsible for all current and
-future development of PostgreSQL.<P>
-
-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.<P>
-
-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.<P>
-
-It is pronounced <I>Post-Gres-Q-L.</I>
-
-<H4><A NAME="1.2">1.2</A>) What's the copyright on
-PostgreSQL?</H4><P>
-
-PostgreSQL is subject to the following COPYRIGHT.<P>
-
-PostgreSQL Data Base Management System<P>
-
-Portions copyright (c) 1996-2000, PostgreSQL, Inc
-
-Portions Copyright (c) 1994-6 Regents of the University of California<P>
-
-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.<P>
-
-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.<P>
-
-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.<P>
-
-
-
-<H4><A NAME="1.3">1.3</A>) What Unix platforms does PostgreSQL run
-on?</H4><P>
-
-The authors have compiled and tested PostgreSQL on the following
-platforms (some of these compiles require gcc):
-<UL>
-<LI> aix - IBM on AIX 3.2.5 or 4.x
-<LI> alpha - DEC Alpha AXP on Digital Unix 2.0, 3.2, 4.0
-<LI> BSD44_derived - OSs derived from 4.4-lite BSD (NetBSD, FreeBSD)
-<LI> bsdi - BSD/OS 2.x, 3.x, 4.x
-<LI> dgux - DG/UX 5.4R4.11
-<LI> hpux - HP PA-RISC on HP-UX 9.*, 10.*
-<LI> i386_solaris - i386 Solaris
-<LI> irix5 - SGI MIPS on IRIX 5.3
-<LI> linux - Intel i86
- Alpha
- SPARC
- PPC
- M68k
-<LI> sco - SCO 3.2v5
- Unixware
-<LI> sparc_solaris - SUN SPARC on Solaris 2.4, 2.5, 2.5.1
-<LI> sunos4 - SUN SPARC on SunOS 4.1.3
-<LI> svr4 - Intel x86 on Intel SVR4 and MIPS
-<LI> ultrix4 - DEC MIPS on Ultrix 4.4
-</UL>
-<P>
-
-<H4><A NAME="1.4">1.4</A>) What non-unix ports are available?</H4><P>
-
-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.<P>
-
-A file <I>win31.mak</I> is included in the distribution for making a
-Win32 libpq library and psql.<P>
-
-The database server is now working on Windows NT using the Cygnus
-Unix/NT porting library. See pgsql/doc/README.NT in the distribution.<P>
-There is also a web page at <A HREF=
-"http://www.freebsd.org/~kevlo/postgres/portNT.html">
-http://www.freebsd.org/~kevlo/postgres/portNT.html.</A>
-
-There is another port using U/Win at <A HREF=
-"http://surya.wipro.com/uwin/ported.html">http://surya.wipro.com/uwin/ported.html.</A>
-
-
-<H4><A NAME="1.5">1.5</A>) Where can I get PostgreSQL?</H4><P>
-The primary anonymous ftp site for PostgreSQL is
-<A
-HREF="ftp://ftp.postgreSQL.org/pub">ftp://ftp.postgreSQL.org/pub</A>
-<P>
-For mirror sites, see our main web site.
-
-<H4><A NAME="1.6">1.6</A>) Where can I get support for PostgreSQL?</H4><P>
-
-There is no official support for PostgreSQL from the University of
-California, Berkeley. It is maintained through volunteer effort.<P>
-
-The main mailing list is: <A
-HREF="mailto:pgsql-general@postgreSQL.org">pgsql-general@postgreSQL.org</A>.
-It is available for discussion of matters pertaining to PostgreSQL.
-To subscribe, send a mail with the lines in the body (not
-the subject line)
-
-<PRE>
- subscribe
- end
-</PRE><P>
-
-to <A
-HREF="mailto:pgsql-general-request@postgreSQL.org">pgsql-general-request@postgreSQL.org</A>.<P>
-
-There is also a digest list available. To subscribe to this list, send
-email to: <A HREF="mailto:pgsql-general-digest-request@postgreSQL.org">
-pgsql-general-digest-request@postgreSQL.org</A> with a BODY of:
-
-<PRE>
- subscribe
- end
-</PRE>
-
-Digests are sent out to members of this list whenever the main list has
-received around 30k of messages.<P>
-
-The bugs mailing list is available. To subscribe to this list, send email
-to <A
-HREF="mailto:bugs-request@postgreSQL.org">bugs-request@postgreSQL.org</A>
-with a BODY of:<P>
-
-<PRE>
- subscribe
- end
-</PRE>
-
-There is also a developers discussion mailing list available. To
-subscribe to this list, send email to <A
-HREF="mailto:hackers-request@postgreSQL.org">hackers-request@postgreSQL.org</A>
-with a BODY of:<P>
-
-<PRE>
- subscribe
- end
-</PRE><P>
-
-Additional mailing lists and information about PostgreSQL can be found
-via the PostgreSQL WWW home page at:
-
-<BLOCKQUOTE>
-<A HREF="http://postgreSQL.org">http://postgreSQL.org</A>
-</BLOCKQUOTE><P>
-
-There is also an IRC channel on EFNet, channel #PostgreSQL.
-I use the unix command <CODE>irc -c '#PostgreSQL' "$USER"
-irc.phoenix.net</CODE><P>
-
-Commercial support for PostgreSQL is available at <A
-HREF="http://www.pgsql.com">http://www.pgsql.com/</A><P>
-
-
-<H4><A NAME="1.7">1.7</A>) What is the latest release of PostgreSQL?</H4><P>
-
-The latest release of PostgreSQL is version 7.0.2.<P>
-
-We plan to have major releases every four months.<P>
-
-
-<H4><A NAME="1.8">1.8</A>) What documentation is available for PostgreSQL?</H4><P>
-
-Several manuals, manual pages, and some small test examples are
-included in the distribution. See the /doc directory. You can also
-browse the manual on-line at <A
-HREF="http://www.postgresql.org/docs/postgres">
-http://www.postgresql.org/docs/postgres.</A>
-in the distribution.
-<P>
-
-There is a PostgreSQL book availiable at <A
-HREF="http://www.postgresql.org/docs/awbook.html">
-http://www.postgresql.org/docs/awbook.html</A><P>
-
-<I>psql</I> has some nice \d commands to show information about types,
-operators, functions, aggregates, etc.<P>
-
-The web site contains even more documentation.<P>
-
-<H4><A NAME="1.9">1.9</A>) How do I find out about known bugs or missing features?
-</H4><P>
-
-PostgreSQL supports an extended subset of SQL-92. See our
-<A HREF="http://www.postgreSQL.org/docs/todo.html">
-TODO</A> for a list of known bugs, missing features, and future plans.<P>
-
-<H4><A NAME="1.10">1.10</A>) How can I learn SQL?</H4><P>
-
-The PostgreSQL book at <A
-HREF="http://www.postgresql.org/docs/awbook.html">
-http://www.postgresql.org/docs/awbook.html</A> teaches SQL.
-
-There is a nice tutorial at <A
-HREF="http://w3.one.net/~jhoffman/sqltut.htm">
-http://w3.one.net/~jhoffman/sqltut.htm</A> and at <A
-HREF="http://ourworld.compuserve.com/homepages/graeme_birchall/HTM_COOK.HTM">
-http://ourworld.compuserve.com/homepages/graeme_birchall/HTM_COOK.HTM.</A><P>
-
-Another one is "Teach Yourself SQL in 21 Days, Second Edition" at <A
-HREF="http://members.tripod.com/er4ebus/sql/index.htm">
-http://members.tripod.com/er4ebus/sql/index.htm </A><P>
-
-Many of our users like <I>The Practical SQL Handbook</I>, Bowman et al.,
-Addison Wesley. Others like <I>The Complete Reference SQL</I>, Groff et al.,
-McGraw-Hill.<P>
-
-
-<H4><A NAME="1.11">1.11</A>) Is PostgreSQL Y2K compliant?</H4><P>
-
-Yes, we easily handle dates past the year 2000AD, and before 2000BC.<P>
-
-
-<H4><A NAME="1.12">1.12</A>) How do I join the development team?</H4><P>
-
-First, download the latest sources 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.<P>
-
-There are about a dozen people who have <SMALL>COMMIT</SMALL> privileges to
-the PostgreSQL CVS archive. All of them have submitted so many
-high-quality patches that it was a pain for the existing
-committers to keep up, and we had confidence that patches they
-committed were likely to be of high quality.
-
-<H4><A NAME="1.13">1.13</A>) How do I submit a bug report?</H4><P>
-
-Fill out the "bug-template" file and send it to: <A
-HREF="mailto:bugs@postgreSQL.org">bugs@postgreSQL.org</A><P>
-
-Also check out our ftp site <A
-HREF="ftp://ftp.postgreSQL.org/pub">ftp://ftp.postgreSQL.org/pub</A> to
-see if there is a more recent PostgreSQL version or patches.<P>
-
-
-<H4><A NAME="1.14">1.14</A>) How does PostgreSQL compare to other
-DBMS's?</H4><P>
-
-There are several ways of measuring software: features, performance,
-reliability, support, and price.<P>
-
-<DL>
-<DT> <B>Features</B>
-<DD>
-
-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 for our next release.<BR><BR>
-
-<DT> <B>Performance</B>
-<DD>
-
-PostgreSQL runs in two modes. Normal <I>fsync</I> 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 <I>no-fsync</I> 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 mode is select-able by
-the database administrator.<BR><BR>
-
-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 <I>Features</I>
-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 <a href="http://openacs.org/why-not-mysql.html">
-http://openacs.org/why-not-mysql.html</a><BR><BR>
-
-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.<BR><BR>
-
-<DT> <B>Reliability</B>
-<DD>
-
-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.<BR><BR>
-
-<DT> <B>Support</B>
-<DD>
-
-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.)<BR><BR>
-
-<DT> <B>Price</B>
-<DD>
-
-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.<BR><BR>
-</DL>
-
-<HR>
-
-<H2><CENTER>User Client Questions</CENTER></H2>
-<P>
-
-
-
-<H4><A NAME="2.1">2.1</A>) Are there ODBC drivers for PostgreSQL?</H4><P>
-
-There are two ODBC drivers available, PsqlODBC and OpenLink ODBC.<P>
-
-PsqlODBC is included in the distribution. More information about it can
-be gotten from: <A HREF="ftp://ftp.postgresql.org/pub/odbc/index.html">
-ftp://ftp.postgresql.org/pub/odbc/index.html</A><P>
-
-OpenLink ODBC can be gotten from <A HREF="http://www.openlinksw.com/">
-http://www.openlinksw.com</A>. 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).<P>
-
-They will probably be selling this product to people who need
-commercial-quality support, but a freeware version will always be
-available. Questions to <A
-HREF="mailto:postgres95@openlink.co.uk">postgres95@openlink.co.uk</A>.<P>
-
-See also the <A HREF="http://www.postgresql.org/docs/programmer/odbc.htm">
-ODBC chapter of the Programmer's Guide</A>.<P>
-
-
-<H4><A NAME="2.2">2.2</A>) What tools are available for hooking
-PostgreSQL to Web pages?</H4><P>
-
-A nice introduction to Database-backed Web pages can be seen at: <A
-HREF="http://www.webtools.com">http://www.webtools.com</A><P>
-
-There is also one at <A HREF="http://www.phone.net/home/mwm/hotlist/">
-http://www.phone.net/home/mwm/hotlist/.</A><P>
-
-For web integration, PHP is an excellent interface. It is at:
-<A HREF="http://www.php.net">http://www.php.net</A><P>
-
-PHP is great for simple stuff, but for more complex cases, many
-use the perl interface and CGI.pm.<P>
-
-A WWW gateway based on WDB using perl can be downloaded from <A
-HREF="http://www.eol.ists.ca/~dunlop/wdb-p95">http://www.eol.ists.ca/~dunlop/wdb-p95</A>
-
-<H4><A NAME="2.3">2.3</A>) Does PostgreSQL have a graphical user interface?
-A report generator? An embedded query language interface?</H4><P>
-
-We have a nice graphical user interface called <I>pgaccess,</I> which is
-shipped as part of the distribution. <I>Pgaccess</I> also has a report
-generator. The web page is <A HREF=
-"http://www.flex.ro/pgaccess">http://www.flex.ro/pgaccess</A><P>
-
-We also include <I>ecpg,</I> which is an embedded SQL query language interface for
-C.
-
-<H4><A NAME="2.4">2.4</A>) What languages are available to
-communicate with PostgreSQL?</H4><P>
-
-We have:
-<UL>
-<LI>C(libpq)
-<LI>C++(libpq++)
-<LI>Embedded C(ecpg)
-<LI>Java(jdbc)
-<LI>Perl(perl5)
-<LI>ODBC(odbc)
-<LI>Python(PyGreSQL)
-<LI>TCL(libpgtcl)
-<LI>C Easy API(libpgeasy)
-<LI>Embedded HTML(<A HREF="http://www.php.net">PHP from http://www.php.net</A>)
-</UL><P>
-
-<HR>
-
-<H2><CENTER>Administrative Questions</CENTER></H2><P>
-
-
-<H4><A NAME="3.1">3.1</A>) Why does initdb fail?</H4><P>
-
-<UL>
-<LI> check that you don't have any of the previous version's binaries in
-your path
-<LI> check to see that you have the proper paths set
-<LI> check that the <I>postgres</I> user owns the proper files
-</UL><P>
-
-
-<H4><A NAME="3.2">3.2</A>) How do I install PostgreSQL somewhere
-other than /usr/local/pgsql?</H4><P>
-
-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.<P>
-
-
-<H4><A NAME="3.3">3.3</A>) When I start the postmaster, I get a <I>Bad
-System Call</I> or core dumped message. Why?</H4><P>
-
-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.<P>
-
-
-<H4><A NAME="3.4">3.4</A>) When I try to start the postmaster, I
-get <I>IpcMemoryCreate</I> errors. Why?</H4><P>
-
-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
-and backend processes you configure postmaster to run with.
-For most systems, with default numbers of buffers and processes, you
-need a minimum of ~1MB.<P>
-
-<H4><A NAME="3.5">3.5</A>) When I try to start the postmaster, I
-get <I>IpcSemaphoreCreate</I> errors. Why?</H4><P>
-
-If the error message is <I>IpcSemaphoreCreate: semget failed (No space
-left on device)</I> 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 <I>-N</I> with a parameter less
-than the default of 32. A more permanent solution is to increase your
-kernel's <SMALL>SEMMNS</SMALL> and <SMALL>SEMMNI</SMALL> parameters.<P>
-
-If the error message is something else, you might not have semaphore
-support configured in your kernel at all.<P>
-
-
-<H4><A NAME="3.6">3.6</A>) How do I prevent other hosts from
-accessing my PostgreSQL database?</H4><P>
-
-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>-i</I> flag to the <I>postmaster,</I>
-<B>and</B> enable host-based authentication by modifying the file
-<I>$PGDATA/pg_hba.conf</I> accordingly. This will allow TCP/IP connections.
-<P>
-
-<H4><A NAME="3.7">3.7</A>) Why can't I connect to my database from
-another machine?</H4><P>
-
-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>-i</I> option, and add an
-appropriate host entry to the file
-<I>pgsql/data/pg_hba.conf</I>. See the <I>pg_hba.conf</I> manual page.<P>
-
-
-<H4><A NAME="3.8">3.8</A>) Why can't I access the database as the <I>root</I>
-user?</H4><P>
-
-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.<P>
-
-
-<H4><A NAME="3.9">3.9</A>) All my servers crash under concurrent
-table access. Why?</H4><P>
-
-This problem can be caused by a kernel that is not configured to support
-semaphores.<P>
-
-
-<H4><A NAME="3.10">3.10</A>) How do I tune the database engine for
-better performance?</H4><P>
-
-Certainly, indices can speed up queries. The <SMALL>EXPLAIN</SMALL> command
-allows you to see how PostgreSQL is interpreting your query, and which
-indices are being used.<P>
-
-If you are doing a lot of <SMALL>INSERTs</SMALL>, consider doing them in a large
-batch using the <SMALL>COPY</SMALL> command. This is much faster than single
-individual <SMALL>INSERTS.</SMALL> Second, statements not in a <SMALL>BEGIN
-WORK/COMMIT</SMALL> 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.<P>
-
-There are several tuning things that can be done. You can disable
-fsync() by starting the postmaster with a <I>-o -F</I> option. This will
-prevent <I>fsync()'s</I> from flushing to disk after every transaction.<P>
-
-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 up because you've exceeded
-your kernel's limit on shared memory space.
-Each buffer is 8K and the default is 64 buffers.<P>
-
-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).<P>
-
-You can also use the <SMALL>CLUSTER</SMALL> command to group data in base tables to
-match an index. See the cluster(l) manual page for more details.<P>
-
-
-<H4><A NAME="3.11">3.11</A>) What debugging features are available in
-PostgreSQL?</H4><P>
-
-PostgreSQL has several features that report status information that can
-be valuable for debugging purposes.<P>
-
-First, by running configure with the --enable-cassert option, many
-<I>assert()'s</I> monitor the progress of the backend and halt the program when
-something unexpected occurs.<P>
-
-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:
-<PRE>
- cd /usr/local/pgsql
- ./bin/postmaster >server.log 2>&1 &
-</PRE><P>
-
-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.<P>
-
-If the <i>postmaster</i> is not running, you can actually run the
-postgres backend from the command line, and type your SQL statement
-directly. This is recommended <B>only</B> 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.<P>
-
-If the <i>postmaster</i> is running, start <I>psql</I> in one window,
-then find the <small>PID</small> of the <i>postgres</i> process used by
-<i>psql.</i> Use a debugger to attach to the <i>postgres</i>
-<small>PID.</small> You can set breakpoints in the debugger and issue
-queries from <i>psql.</i> If you are debugging <i>postgres</i> startup,
-you can set PGOPTIONS="-W n", then start <i>psql.</i> This will cause
-startup to delay for <i>n</i> seconds so you can attach with the
-debugger and trace through the startup sequence.<P>
-
-The postgres program has -s, -A, and -t options that can be very useful
-for debugging and performance measurements.<P>
-
-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.<P>
-
-
-<H4><A NAME="3.12">3.12</A>) I get 'Sorry, too many clients' when trying
-to connect. Why?</H4><P>
-
-You need to increase the postmaster's limit on how many concurrent backend
-processes it can start.<P>
-
-In Postgres 6.5 and up, the default limit is 32 processes. You can
-increase it by restarting the postmaster with a suitable <I>-N</I>
-value. With the default configuration you can set <I>-N</I> as large as
-1024; if you need more, increase <SMALL>MAXBACKENDS</SMALL> in
-<I>include/config.h</I> and rebuild. You can set the default value of
-<I>-N</I> at configuration time, if you like, using configure's
-<I>--with-maxbackends</I> switch.<P>
-
-Note that if you make <I>-N</I> larger than 32, you must also increase
-<I>-B</I> 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,
-<SMALL>SHMMAX,</SMALL> the maximum number of semaphores,
-<SMALL>SEMMNS</SMALL> and <SMALL>SEMMNI,</SMALL> the maximum number of
-processes, <SMALL>NPROC,</SMALL> the maximum number of processes per
-user, <SMALL>MAXUPRC,</SMALL> and the maximum number of open files,
-<SMALL>NFILE</SMALL> and <SMALL>NINODE.</SMALL> The reason that Postgres
-has a limit on the number of allowed backend processes is so that you
-can ensure that your system won't run out of resources.<P>
-
-In Postgres versions prior to 6.5, the maximum number of backends was
-64, and changing it required a rebuild after altering the MaxBackendId
-constant in <I>include/storage/sinvaladt.h.</I><P>
-
-<H4><A NAME="3.13">3.13</A>) What are the pg_tempNNN.NN files in my
-database directory?</H4><P>
-
-They are temporary files generated by the query executor. For
-example, if a sort needs to be done to satisfy an <SMALL>ORDER BY,</SMALL> and
-the sort requires more space than the backend's -S parameter allows,
-then temp files are created to hold the extra data.<P>
-
-The temp files should go away automatically, but might not if a backend
-crashes during a sort. If you have no transactions running at the time,
-it is safe to delete the pg_tempNNN.NN files.<P>
-
-<HR>
-
-<H2><CENTER>Operational Questions</CENTER></H2><P>
-
-
-<H4><A NAME="4.1">4.1</A>) The system seems to be confused about
-commas, decimal points, and date formats.</H4><P>
-
-Check your locale configuration. PostgreSQL uses the locale settings 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.<P>
-
-
-<H4><A NAME="4.2">4.2</A>) What is the exact difference between
-binary cursors and normal cursors?</H4><P>
-
-See the <SMALL>DECLARE</SMALL> manual page for a description.<P>
-
-<H4><A NAME="4.3">4.3</A>) How do I <SMALL>SELECT</SMALL> only the first few
-rows of a query?</H4><P>
-
-See the <SMALL>FETCH</SMALL> manual page, or use SELECT ... LIMIT....<P>
-
-The entire query may have to be evaluated, even if you only want the
-first few rows. Consider a query that has an <SMALL>ORDER BY.</SMALL>
-If there is an index that matches the <SMALL>ORDER BY</SMALL>,
-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.<P>
-
-<H4><A NAME="4.4">4.4</A>) How do I get a list of tables, or other
-information I see in <I>psql?</I><BR></H4><P>
-
-You can read the source code for <I>psql,</I> file
-pgsql/src/bin/psql/psql.c. It contains SQL commands that generate the
-output for psql's backslash commands. You can also start <I>psql</I>
-with the <I>-E</I> option so that it will print out the queries it uses
-to execute the commands you give.<P>
-
-
-<H4><A NAME="4.5">4.5</A>) How do you remove a column from a
-table?</H4><P>
-
-We do not support <SMALL>ALTER TABLE DROP COLUMN,</SMALL> but do
-this:
-<PRE>
- 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;
-</PRE><P>
-
-
-
-
-<H4><A NAME="4.6">4.6</A>) What is the maximum size for a
-row, table, database?</H4><P>
-
-These are the limits:
-
-<PRE>
-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 columns table? unlimited
-Maximum number of indexes on a table? unlimited
-</PRE>
-
-Of course, these are not actually unlimited, but limited to available
-disk space.<P>
-
-To change the maximum row size, edit <I>include/config.h</I> and change
-<SMALL>BLCKSZ.</SMALL> To use attributes larger than 8K, you can also
-use the large object interface.<P>
-
-Row length limit will be removed in 7.1.<P>
-
-
-<H4><A NAME="4.7">4.7</A>)How much database disk space is required to
-store data from a typical flat file?<BR></H4><P>
-
-A Postgres database can require about six and a half times the disk space
-required to store the data in a flat file.<P>
-
-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:
-
-<PRE>
- 36 bytes: each row header (approximate)
- + 8 bytes: two int fields @ 4 bytes each
- + 4 bytes: pointer on page to tuple
- ----------------------------------------
- 48 bytes per row
-
- The data page size in PostgreSQL is 8192 bytes (8 KB), so:
-
- 8192 bytes per page
- ------------------- = 171 rows per database page (rounded up)
- 48 bytes per row
-
- 300000 data rows
- -------------------- = 1755 database pages
- 171 rows per page
-
-1755 database pages * 8192 bytes per page = 14,376,960 bytes (14MB)
-</PRE></P>
-
-Indexes do not contain as much overhead, but do contain the data that is
-being indexed, so they can be large also.<P>
-
-<H4><A NAME="4.8">4.8</A>) How do I find out what indices or
-operations are defined in the database?</H4><P>
-
-<I>psql</I> has a variety of backslash commands to show such information. Use
-\? to see them.<P>
-
-Also try the file <I>pgsql/src/tutorial/syscat.source.</I> It
-illustrates many of the <SMALL>SELECT</SMALL>s needed to get information from
-the database system tables.<P>
-
-
-<H4><A NAME="4.9">4.9</A>) My queries are slow or don't make
-use of the indexes. Why?</H4><P>
-
-PostgreSQL does not automatically maintain statistics. One has to make
-an explicit <SMALL>VACUUM</SMALL> call 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.<P>
-
-For column-specific optimization statistics, use <SMALL>VACUUM
-ANALYZE.</SMALL> <SMALL>VACUUM ANALYZE</SMALL> is important for complex
-multi-join 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 <SMALL>VACUUM
-ANALYZE</SMALL> must be run to collect them periodically.<P>
-
-Indexes are usually not used for <SMALL>ORDER BY</SMALL> 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.
-<P>
-
-When using wild-card operators such as <SMALL>LIKE</SMALL> or <I>~,</I> indices can
-only be used if the beginning of the search is anchored to the start of
-the string. So, to use indices, <SMALL>LIKE</SMALL> searches should not
-begin with <I>%,</I> and <I>~</I>(regular expression searches) should
-start with <I>^.</I>
-
-<H4><A NAME="4.10">4.10</A>) How do I see how the query optimizer is
-evaluating my query?</H4><P>
-
-See the <SMALL>EXPLAIN</SMALL> manual page.<P>
-
-<H4><A NAME="4.11">4.11</A>) What is an R-tree index?</H4><P>
-
-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 <I>point,</I>
-the system can more efficient answer queries like select all points
-within a bounding rectangle.<P>
-
-The canonical paper that describes the original R-Tree design is:<P>
-
-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.<P>
-
-You can also find this paper in Stonebraker's "Readings in Database
-Systems"<P>
-
-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.<P>
-
-
-<H4><A NAME="4.12">4.12</A>) What is Genetic Query
-Optimization?</H4><P>
-
-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.<P>
-
-For further information see the documentation.
-
-
-
-<H4><A NAME="4.13">4.13</A>) How do I do regular expression searches and
-case-insensitive regexp searching?</H4><P>
-
-The <I>~</I> operator does regular-expression matching, and <I>~*</I>
-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 <SMALL>LIKE</SMALL> with this:
-<PRE>
- WHERE lower(textfield) LIKE lower(pattern)
-</PRE>
-
-<H4><A NAME="4.14">4.14</A>) In a query, how do I detect if a field
-is NULL?</H4><P>
-
-You test the column with IS NULL and IS NOT NULL.<P>
-
-
-<H4><A NAME="4.15">4.15</A>) What is the difference between the
-various character types?</H4>
-
-<PRE>
-Type Internal Name Notes
---------------------------------------------------
-"char" char 1 character
-CHAR(#) bpchar blank padded to the specified fixed length
-VARCHAR(#) varchar size specifies maximum length, no padding
-TEXT text length limited only by maximum row length
-BYTEA bytea variable-length array of bytes
-</PRE><P>
-
-You will see the internal name when examining system catalogs
-and in some error messages.<P>
-
-The last four types above are "varlena" types (i.e. the first four bytes
-are the length, followed by the data). <I>char(#)</I> allocates the
-maximum number of bytes no matter how much data is stored in the field.
-<I>text, varchar(#),</I> and <I>bytea</I> 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 all columns after the
-first column of this type.<P>
-
-
-<H4><A NAME="4.16.1">4.16.1</A>) How do I create a
-serial/auto-incrementing field?</H4><P>
-
-PostgreSQL supports <SMALL>SERIAL</SMALL> data type. It auto-creates a
-sequence and index on the column. For example, this...
-<PRE>
- CREATE TABLE person (
- id SERIAL,
- name TEXT
- );
-</PRE>
-...is automatically translated into this...
-<PRE>
- 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 );
-</PRE>
-See the <I>create_sequence</I> manual page for more information about sequences.
-
-You can also use each row's <I>oid</I> field as a unique value. However, if
-you need to dump and reload the database, you need to use <I>pg_dump's -o</I>
-option or <SMALL>COPY WITH OIDS</SMALL> option to preserve the oids.<P>
-
-For more details, see Bruce Momjian's chapter on
-<A HREF="http://www.postgresql.org/docs/aw_pgsql_book">Numbering Rows.</A>
-
-<H4><A NAME="4.16.2">4.16.2</A>) How do I get the back the generated SERIAL value after an insert?</H4><P>
-Probably the simplest approach is to to retrieve the next SERIAL value from the sequence object with the <I>nextval()</I> function <I>before</I> inserting and then insert it explicitly. Using the example table in <A HREF="#4.16.1">4.16.1</A>, that might look like this:
-<PRE>
- $newSerialID = nextval('person_id_seq');
- INSERT INTO person (id, name) VALUES ($newSerialID, 'Blaise Pascal');
-</PRE>
-You would then also have the new value stored in <CODE>$newSerialID</CODE> for use in other queries (e.g., as a foreign key to the <CODE>person</CODE> table). Note that the name of the automatically-created SEQUENCE object will be named <<I>table</I>>_<<I>serialcolumn</I>>_<I>seq</I>, where <I>table</I> and <I>serialcolumn</I> are the names of your table and your SERIAL column, respectively.
-<P>
-Similarly, you could retrieve the just-assigned SERIAL value with the <I>currval</I>() function <I>after</I> it was inserted by default, e.g.,
-<PRE>
- INSERT INTO person (name) VALUES ('Blaise Pascal');
- $newID = currval('person_id_seq');
-</PRE>
-Finally, you could use the <A HREF="#4.17">oid</A> returned from the
-INSERT statement to lookup the default value, though this is probably
-the least portable approach. In perl, using DBI with Edmund Mergl's
-DBD::Pg module, the oid value is made available via
-$sth->{pg_oid_status} after $sth->execute().
-
-<H4><A NAME="4.16.3">4.16.3</A>) Don't currval() and nextval() lead to a race condition with other
-concurrent backend processes?</H4><P>
-
-No. That has been handled by the backends.
-
-
-<H4><A NAME="4.17">4.17</A>) What is an oid? What is a tid?</H4><P>
-
-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 <I>backend/access/transam.h</I>). All
-user-created oids are equal or greater that this. By default, all these
-oids are unique not only within a table, or database, but unique within
-the entire PostgreSQL installation.<P>
-
-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. See the <I>sql(l)</I> manual page to see the other internal columns.
-You can create an index on the oid field for faster access.<P>
-
-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:
-
-<PRE>
- CREATE TABLE new_table(old_oid oid, mycol int);
- SELECT INTO new SELECT old_oid, mycol FROM old;
- COPY new TO '/tmp/pgtable';
- DELETE FROM new;
- COPY new WITH OIDS FROM '/tmp/pgtable';
-<!--
- CREATE TABLE new_table (mycol int);
- INSERT INTO new_table (oid, mycol) SELECT oid, mycol FROM old_table;
--->
-</PRE><P>
-
-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.<P>
-
-
-<H4><A NAME="4.18">4.18</A>) What is the meaning of some of the terms
-used in PostgreSQL?</H4><P>
-
-Some of the source code and older documentation use terms that have more
-common usage. Here are some:
-
-<UL>
-<LI> table, relation, class
-<LI> row, record, tuple
-<LI> column, field, attribute
-<LI> retrieve, select
-<LI> replace, update
-<LI> append, insert
-<LI> oid, serial value
-<LI> portal, cursor
-<LI> range variable, table name, table alias
-</UL><P>
-
-<H4><A NAME="4.19">4.19</A>) Why do I get the error "FATAL: palloc
-failure: memory exhausted?"<BR></H4><P>
-
-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:
-
-<PRE>
- ulimit -d 65536
- limit datasize 64m
-</PRE>
-
-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.<P>
-
-<H4><A NAME="4.20">4.20</A>) How do I tell what PostgreSQL version I
-am running? <BR></H4><P>
-
-From <I>psql,</I> type <CODE>select version();</CODE><P>
-
-<H4><A NAME="4.21">4.21</A>) My large-object operations get <I>invalid
-large obj descriptor.</I> Why? <BR></H4><P>
-
-You need to put <CODE>BEGIN WORK</CODE> and <CODE>COMMIT
-</CODE> around any use of a large object handle, that is,
-surrounding <CODE>lo_open</CODE> ... <CODE>lo_close.</CODE><P>
-
-Current PostgreSQL enforces the rule by closing large object handles at
-transaction commit, which will be instantly upon completion of the
-<I>lo_open</I> command if you are not inside a transaction. So the
-first attempt to do anything with the handle will draw <I>invalid large
-obj descriptor.</I> 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.<P>
-
-If you are using a client interface like ODBC you may need to set
-<CODE>auto-commit off.</CODE><P>
-
-<H4><A NAME="4.22">4.22</A>) How do I create a column that will default to the
-current time?<BR></H4><P>
-Use <i>now()</i>:
-<CODE><PRE>
- CREATE TABLE test (x int, modtime timestamp default now() );
-</PRE></CODE>
-<P>
-<H4><A NAME="4.23">4.23</A>) Why are my subqueries using <CODE>IN</CODE> so
-slow?<BR></H4><P>
-Currently, we join subqueries to outer queries by sequential scanning
-the result of the subquery for each row of the outer query. A workaround
-is to replace <CODE>IN</CODE> with <CODE>EXISTS</CODE>. For example,
-change:
-<CODE><PRE>
- SELECT *
- FROM tab
- WHERE col1 IN (SELECT col2 FROM TAB2)
-</PRE></CODE>
-to:
-<CODE><PRE>
- SELECT *
- FROM tab
- WHERE EXISTS (SELECT col2 FROM TAB2 WHERE col1 = col2)
-</PRE></CODE>
-We hope to fix this limitation in a future release.
-
-<H4><A NAME="4.24">4.24</A>) How do I do an <i>outer</i> join?<BR></H4><P>
-PostgreSQL does not support outer joins in the current release. They can
-be simulated using <small>UNION</small> and <small>NOT IN</small>. For
-example, when joining <i>tab1</i> and <i>tab2,</i> the following query
-does an <i>outer</i> join of the two tables:
-<PRE>
- 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
-</PRE>
-
-<HR>
-
-<H2><CENTER>Extending PostgreSQL</CENTER></H2><P>
-
-
-<H4><A NAME="5.1">5.1</A>) I wrote a user-defined function. When
-I run it in <I>psql,</I> why does it dump core?</H4><P>
-
-The problem could be a number of things. Try testing your user-defined
-function in a stand alone test program first.
-
-<H4><A NAME="5.2">5.2</A>) What does the message:
-<I>NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!</I> mean?</H4><P>
-
-You are <I>pfree'ing</I> something that was not <I>palloc'ed.</I>
-Beware of mixing <I>malloc/free</I> and <I>palloc/pfree.</I>
-
-
-<H4><A NAME="5.3">5.3</A>) How can I contribute some nifty new types and
-functions for PostgreSQL?</H4><P>
-
-
-Send your extensions to the pgsql-hackers mailing list, and they will
-eventually end up in the <I>contrib/</I> subdirectory.<P>
-
-
-<H4><A NAME="5.4">5.4</A>) How do I write a C function to return a
-tuple?</H4><P>
-
-This requires wizardry so extreme that the authors have never
-tried it, though in principle it can be done.<P>
-
-<H4><A NAME="5.5">5.5</A>) I have changed a source file. Why does the
-recompile does not see the change?</H4><P>
-
-The Makefiles do not have the proper dependencies for include files. You
-have to do a <I>make clean</I> and then another <I>make</I>.
- You
-have to do a <I>make clean</I> and then another <I>make.</I><P>
-
-
-</BODY>
-</HTML>
-
+++ /dev/null
-<HTML>
-<HEAD>
-<TITLE>PostgreSQL Developers FAQ</title>
-</HEAD>
-<BODY BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#FF0000" VLINK="#A00000" ALINK="#0000FF">
-<H1>
-Developer's Frequently Asked Questions (FAQ) for PostgreSQL
-</H1>
-<P>
-Last updated: Fri Jun 9 21:54:54 EDT 2000
-<P>
-Current maintainer: Bruce Momjian (<a
-href="mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</a>)<BR>
-<P>
-The most recent version of this document can be viewed at
-the postgreSQL Web site, <a
-href="http://PostgreSQL.org">http://PostgreSQL.org</a>.
-<P>
-<HR>
-<P>
-
-<CENTER><H2>Questions</H2></CENTER>
-<a href="#1">1</a>) What tools are available for developers?<BR>
-<a href="#2">2</a>) What books are good for developers?<BR>
-<a href="#3">3</a>) Why do we use <I>palloc</I>() and <I>pfree</I>() to allocate memory?<BR>
-<a href="#4">4</a>) Why do we use <I>Node</I> and <I>List</I> to
-make data structures?<BR>
-<a href="#5">5</a>) How do I add a feature or fix a bug?<BR>
-<a href="#6">6</a>) How do I download/update the current source tree?<BR>
-<a href="#7">7</a>) How do I test my changes?<BR>
-<a href="#7">7</a>) I just added a field to a structure. What else
-should I do?<BR>
-<a href="#8">8</a>) Why are table, column, type, function, view
-names sometimes referenced as <I>Name</I> or <I>NameData,</I> and
-sometimes as <I>char *?</I><BR>
-<a href="#9">9</a>) How do I efficiently access information in
-tables from the backend code?<BR>
-<a href="#10">10</a>) What is elog()?<BR>
-<a href="#11">11</a>) What is configure all about?<BR>
-<a href="#12">12</a>) How do I add a new port?<BR>
-<BR>
-<HR>
-
-<H3><a
-name="1">1</a>) What tools are available for developers?</H3><P>
-
-Aside from the User documentation mentioned in the regular FAQ, there
-are several development tools available. First, all the files in the
-<I>/tools</I> directory are designed for developers.
-
-<PRE>
- RELEASE_CHANGES changes we have to make for each release
- SQL_keywords standard SQL'92 keywords
- backend description/flowchart of the backend directories
- ccsym find standard defines made by your compiler
- entab converts tabs to spaces, used by pgindent
- find_static finds functions that could be made static
- find_typedef get a list of typedefs in the source code
- make_ctags make vi 'tags' file in each directory
- make_diff make *.orig and diffs of source
- make_etags make emacs 'etags' files
- make_keywords.README make comparison of our keywords and SQL'92
- make_mkid make mkid ID files
- mkldexport create AIX exports file
- pgindent indents C source files
- pginclude scripts for adding/removing include files
- unused_oids in pgsql/src/include/catalog
-</PRE>
-
-Let me note some of these. If you point your browser at the
-<I>file:/usr/local/src/pgsql/src/tools/backend/index.html</I> directory,
-you will see few paragraphs describing the data flow, the backend
-components in a flow chart, and a description of the shared memory area.
-You can click on any flowchart box to see a description. If you then
-click on the directory name, you will be taken to the source directory,
-to browse the actual source code behind it. We also have several README
-files in some source directories to describe the function of the module.
- The browser will display these when you enter the directory also. The
-<I>tools/backend</I> directory is also contained on our web page under
-the title <I>How PostgreSQL Processes a Query.</I><P>
-
-
-Second, you really should have an editor that can handle tags, so you
-can tag a function call to see the function definition, and then tag
-inside that function to see an even lower-level function, and then back
-out twice to return to the original function. Most editors support this
-via <I>tags</I> or <I>etags</I> files.<P>
-
-
-Third, you need to get <I>id-utils</I> from:
-<pre>
- <a href="ftp://alpha.gnu.org/gnu/id-utils-3.2d.tar.gz">ftp://alpha.gnu.org/gnu/id-utils-3.2d.tar.gz</a>
- <a href="ftp://tug.org/gnu/id-utils-3.2d.tar.gz">ftp://tug.org/gnu/id-utils-3.2d.tar.gz</a>
- <a href="ftp://ftp.enst.fr/pub/gnu/gnits/id-utils-3.2d.tar.gz">ftp://ftp.enst.fr/pub/gnu/gnits/id-utils-3.2d.tar.gz</a>
-</pre>
-
-By running <I>tools/make_mkid</I>, an archive of source symbols can be
-created that can be rapidly queried like <I>grep</I> or edited. Others
-prefer <I>glimpse.</I><P>
-
-
-<I>make_diff</I> has tools to create patch diff files that can be
-applied to the distribution.<P>
-
-
-Our standard format is to indent each code level with one tab, where
-each tab is four spaces. You will need to set your editor to display
-tabs as four spaces:
-<BR>
-<PRE>
- vi in ~/.exrc:
- set tabstop=4
- set sw=4
- more:
- more -x4
- less:
- less -x4
- emacs:
- M-x set-variable tab-width
- or
- ; Cmd to set tab stops &etc for working with PostgreSQL code
- (c-add-style "pgsql"
- '("bsd"
- (indent-tabs-mode . t)
- (c-basic-offset . 4)
- (tab-width . 4)
- (c-offsets-alist .
- ((case-label . +))))
- t) ; t = set this mode on
-
- and add this to your autoload list (modify file path in macro):
-
- (setq auto-mode-alist
- (cons '("\\`/usr/local/src/pgsql/.*\\.[chyl]\\'" . pgsql-c-mode)
- auto-mode-alist))
- or
- /*
- * Local variables:
- * tab-width: 4
- * c-indent-level: 4
- * c-basic-offset: 4
- * End:
- */
-</PRE>
-<BR>
-<I>pgindent</I> will the format code by specifying
-flags to your operating system's utility <I>indent.</I><P>
-<I>pgindent</I> is run on all source files just before each beta test
-period. It auto-formats all source files to make them consistent.
-Comment blocks that need specific line breaks should be formatted as
-<I>block comments,</I> where the comment starts as
-<CODE>/*------</CODE>. These comments will not be reformatted in any
-way.
-
-<I>pginclude</I> contains scripts used to add needed #include's to
-include files, and removed unneeded #include's.
-
-When adding system types, you will need to assign oids to them.
-There is also a script called <I>unused_oids</I> in
-<I>pgsql/src/include/catalog</I> that shows the unused oids.
-
-<H3><a name="2">2</a>) What books are good for developers?</H3><P>
-
-I have four good books, <I>An Introduction to Database Systems,</I> by
-C.J. Date, Addison, Wesley, <I>A Guide to the SQL Standard,</I> by C.J.
-Date, et. al, Addison, Wesley, <I>Fundamentals of Database Systems,</I>
-by Elmasri and Navathe, and <I>Transaction Processing,</I> by Jim Gray,
-Morgan, Kaufmann<P>
-
-There is also a database performance site, with a handbook on-line
-written by Jim Gray at <A
-HREF="http://www.benchmarkresources.com">http://www.benchmarkresources.com.</A>
-
-
-
-<H3><a name="3">3</a>) Why do we use <I>palloc</I>() and <I>pfree</I>()
-to allocate memory?</H3><P>
-
-<I>palloc()</I> and <I>pfree()</I> are used in place of malloc() and
-free() because we automatically free all memory allocated when a
-transaction completes. This makes it easier to make sure we free memory
-that gets allocated in one place, but only freed much later. There are
-several contexts that memory can be allocated in, and this controls when
-the allocated memory is automatically freed by the backend.<P>
-
-
-<H3><a name="4">4</a>) Why do we use <I>Node</I> and <I>List</I> to
-make data structures?</H3><P>
-
-We do this because this allows a consistent way to pass data inside the
-backend in a flexible way. Every node has a <I>NodeTag</I> which
-specifies what type of data is inside the Node. <I>Lists</I> are groups
-of <I>Nodes chained together as a forward-linked list.</I><P>
-Here are some of the <I>List</I> manipulation commands:
-<BLOCKQUOTE>
-<DL>
-<DT>lfirst(i)
-<DD>return the data at list element <I>i.</I>
-<DT>lnext(i)
-<DD>return the next list element after <I>i.</I>
-<DT>foreach(i, list)
-<DD>loop through <I>list,</I> assigning each list element to <I>i.</I>
-It is important to note that <I>i</I> is a List *, not the data in the
-<I>List</I> element. You need to use <I>lfirst(i)</I> to get at the data.
-Here is a typical code snipped that loops through a List containing
-<I>Var *'s</I> and processes each one:
-<PRE>
-<CODE>
- List *i, *list;
-
- foreach(i, list)
- {
- Var *var = lfirst(i);
-
- /* process var here */
- }
-</CODE>
-</PRE>
-<DT>lcons(node, list)
-<DD>add <I>node</I> to the front of <I>list,</I> or create a new list with
-<I>node</I> if <I>list</I> is <I>NIL.</I>
-<DT>lappend(list, node)
-<DD>add <I>node</I> to the end of <I>list.</I> This is more expensive
-that lcons.
-<DT>nconc(list1, list2)
-<DD>Concat <I>list2</I> on to the end of <I>list1.</I>
-<DT>length(list)
-<DD>return the length of the <I>list.</I>
-<DT>nth(i, list)
-<DD>return the <I>i</I>'th element in <I>list.</I>
-<DT>lconsi, ...
-<DD>There are integer versions of these: <I>lconsi, lappendi, nthi.</I>
-<I>List's</I> containing integers instead of Node pointers are used to
-hold list of relation object id's and other integer quantities.
-</DL>
-</BLOCKQUOTE>
-You can print nodes easily inside <I>gdb.</I> First, to disable
-output truncation when you use the gdb <I>print</I> command:
-<PRE>
-<CODE>
- (gdb) set print elements 0
-</CODE>
-</PRE>
-Instead of printing values in gdb format, you can use the next two
-commands to print out List, Node, and structure contents in a verbose
-format that is easier to understand. List's are unrolled into nodes,
-and nodes are printed in detail. The first prints in a short format,
-and the second in a long format:
-<PRE>
-<CODE>
- (gdb) call print(any_pointer)
- (gdb) call pprint(any_pointer)
-</CODE>
-</PRE>
-The output appears in the postmaster log file, or on your screen if you
-are running a backend directly without a postmaster.
-<P>
-
-<H3><a name="5">5</a>) How do I add a feature or fix a bug?</H3><P>
-
-The source code is over 250,000 lines. Many problems/features are
-isolated to one specific area of the code. Others require knowledge of
-much of the source. If you are confused about where to start, ask the
-hackers list, and they will be glad to assess the complexity and give
-pointers on where to start.<P>
-
-Another thing to keep in mind is that many fixes and features can be
-added with surprisingly little code. I often start by adding code, then
-looking at other areas in the code where similar things are done, and by
-the time I am finished, the patch is quite small and compact.<P>
-
-When adding code, keep in mind that it should use the existing
-facilities in the source, for performance reasons and for simplicity.
-Often a review of existing code doing similar things is helpful.<P>
-
-
-<H3><a name="6">6</a>) How do I download/update the current source
-tree?</H3><P>
-
-
-There are several ways to obtain the source tree. Occasional developers
-can just get the most recent source tree snapshot from
-ftp.postgresql.org. For regular developers, you can use CVS. CVS
-allows you to download the source tree, then occasionally update your
-copy of the source tree with any new changes. Using CVS, you don't have
-to download the entire source each time, only the changed files.
-Anonymous CVS does not allows developers to update the remote source
-tree, though privileged developers can do this. There is a CVS FAQ on
-our web site that describes how to use remote CVS. You can also use
-CVSup, which has similarly functionality, and is available from
-ftp.postgresql.org.<P>
-
-To update the source tree, there are two ways. You can generate a patch
-against your current source tree, perhaps using the make_diff tools
-mentioned above, and send them to the patches list. They will be
-reviewed, and applied in a timely manner. If the patch is major, and we
-are in beta testing, the developers may wait for the final release
-before applying your patches.<P>
-
-For hard-core developers, Marc(scrappy@postgresql.org) will give you a
-Unix shell account on postgresql.org, so you can use CVS to update the
-main source tree, or you can ftp your files into your account, patch,
-and cvs install the changes directly into the source tree. <P>
-
-<H3><a name="6">6</a>) How do I test my changes?</H3><P>
-
-First, use <I>psql</I> to make sure it is working as you expect. Then
-run <I>src/test/regress</I> and get the output of
-<I>src/test/regress/checkresults</I> with and without your changes, to
-see that your patch does not change the regression test in unexpected
-ways. This practice has saved me many times. The regression tests test
-the code in ways I would never do, and has caught many bugs in my
-patches. By finding the problems now, you save yourself a lot of
-debugging later when things are broken, and you can't figure out when it
-happened.<P>
-
-
-<H3><a name="7">7</a>) I just added a field to a structure. What else
-should I do?</H3><P>
-
-The structures passing around from the parser, rewrite, optimizer, and
-executor require quite a bit of support. Most structures have support
-routines in <I>src/backend/nodes</I> used to create, copy, read, and output
-those structures. Make sure you add support for your new field to these
-files. Find any other places the structure may need code for your new
-field. <I>mkid</I> is helpful with this (see above).<P>
-
-
-<H3><a name="8">8</a>) Why are table, column, type, function, view
-names sometimes referenced as <I>Name</I> or <I>NameData,</I> and
-sometimes as <I>char *?</I></H3><P>
-
-Table, column, type, function, and view names are stored in system
-tables in columns of type <I>Name.</I> Name is a fixed-length,
-null-terminated type of <I>NAMEDATALEN</I> bytes. (The default value
-for NAMEDATALEN is 32 bytes.)
-
-<PRE><CODE>
- typedef struct nameData
- {
- char data[NAMEDATALEN];
- } NameData;
- typedef NameData *Name;
-</CODE></PRE>
-
-Table, column, type, function, and view names that come into the
-backend via user queries are stored as variable-length, null-terminated
-character strings.<P>
-
-Many functions are called with both types of names, ie. <I>heap_open().</I>
-Because the Name type is null-terminated, it is safe to pass it to a
-function expecting a char *. Because there are many cases where on-disk
-names(Name) are compared to user-supplied names(char *), there are many
-cases where Name and char * are used interchangeably.<P>
-
-<H3><a name="9">9</a>) How do I efficiently access information in
-tables from the backend code?</H3><P>
-
-You first need to find the tuples(rows) you are interested in. There
-are two ways. First, <I>SearchSysCacheTuple()</I> and related functions
-allow you to query the system catalogs. This is the preferred way to
-access system tables, because the first call to the cache loads the
-needed rows, and future requests can return the results without
-accessing the base table. The caches use system table indexes
-to look up tuples. A list of available caches is located in
-<I>src/backend/utils/cache/syscache.c.</I>
-<I>src/backend/utils/cache/lsyscache.c</I> contains many column-specific
-cache lookup functions.<P>
-
-The rows returned are cached-owned versions of the heap rows. They are
-invalidated when the base table changes. Because the cache is local to
-each backend, you may use the pointer returned from the cache for short
-periods without making a copy of the tuple. If you send the pointer
-into a large function that will be doing its own cache lookups, it is
-possible the cache entry may be flushed, so you should use
-<I>SearchSysCacheTupleCopy()</I> in these cases, and <I>pfree()</I> the
-tuple when you are done.<P>
-
-If you can't use the system cache, you will need to retrieve the data
-directly from the heap table, using the buffer cache that is shared by
-all backends. The backend automatically takes care of loading the rows
-into the buffer cache.<P>
-
-Open the table with <I>heap_open().</I> You can then start a table scan
-with <I>heap_beginscan(),</I> then use <I>heap_getnext()</I> and
-continue as long as <I>HeapTupleIsValid()</I> returns true. Then do a
-<I>heap_endscan().</I> <I>Keys</I> can be assigned to the <I>scan.</I>
-No indexes are used, so all rows are going to be compared to the keys,
-and only the valid rows returned.<P>
-
-You can also use <I>heap_fetch()</I> to fetch rows by block
-number/offset. While scans automatically lock/unlock rows from the
-buffer cache, with <I>heap_fetch(),</I> you must pass a <I>Buffer</I>
-pointer, and <I>ReleaseBuffer()</I> it when completed.
-
-Once you have the row, you can get data that is common to all tuples,
-like <I>t_self</I> and <I>t_oid,</I> by merely accessing the
-<I>HeapTuple</I> structure entries.
-
-If you need a table-specific column, you should take the HeapTuple
-pointer, and use the <I>GETSTRUCT()</I> macro to access the
-table-specific start of the tuple. You then cast the pointer as a
-<I>Form_pg_proc</I> pointer if you are accessing the pg_proc table, or
-<I>Form_pg_type</I> if you are accessing pg_type. You can then access
-the columns by using a structure pointer:
-
-<PRE>
-<CODE>
- ((Form_pg_class) GETSTRUCT(tuple))->relnatts
-</CODE>
-</PRE>
-
-You should not directly change <I>live</I> tuples in this way. The best
-way is to use <I>heap_tuplemodify()</I> and pass it your palloc'ed
-tuple, and the values you want changed. It returns another palloc'ed
-tuple, which you pass to <I>heap_replace().</I>
-
-You can delete tuples by passing the tuple's <I>t_self</I> to
-<I>heap_destroy().</I> You can use it for <I>heap_update()</I> too.
-
-Remember, tuples can be either system cache versions, which may go away
-soon after you get them, buffer cache versions, which go away when
-you <I>heap_getnext(),</I> <I>heap_endscan,</I> or
-<I>ReleaseBuffer()</I>, in the <I>heap_fetch()</I> case. Or it may be a
-palloc'ed tuple, that you must <I>pfree()</I> when finished.
-
-<H3><a name="10">10</a>) What is elog()?</H3><P>
-
-<I>elog()</I> is used to send messages to the front-end, and optionally
-terminate the current query being processed. The first parameter is an
-elog level of <I>NOTICE,</I> <I>DEBUG,</I> <I>ERROR,</I> or
-<I>FATAL.</I>
-
-<I>NOTICE</I> prints on the user's terminal and the postmaster logs.
-<I>DEBUG</I> prints only in the postmaster logs. <I>ERROR</I> prints in
-both places, and terminates the current query, never returning from the call.
-<I>FATAL</I> terminates the backend process.
-
-The remaining parameters of <I>elog</I> are a <I>printf</I>-style set of
-parameters to print.
-
-<H3><a name="11">11</a>) What is configure all about?</H3><P>
-
-The files <I>configure</I> and <I>configure.in</I> are part of the
-GNU <I>autoconf</I> package. Configure allows us to test for various
-capabilities of the OS, and to set variables that can then be tested in
-C programs and Makefiles. Autoconf is installed on the PostgreSQL main
-server. To add options to configure, edit <I>configure.in,</I> and then
-run <I>autoconf</I> to generate <I>configure.</I><P>
-
-When <I>configure</I> is run by the user, it tests various OS
-capabilities, stores those in <I>config.status</I> and
-<I>config.cache,</I> and modifies a list of <I>*.in</I> files. For
-example, if there exists a <I>Makefile.in,</I> configure generates a
-<I>Makefile</I> that contains substitutions for all @var@ parameters
-found by configure.<P>
-
-When you need to edit files, make sure you don't waste time modifying
-files generated by <I>configure.</I> Edit the <I>*.in</I> file, and
-re-run <I>configure</I> to recreate the needed file. If you run <I>make
-distclean</I> from the top-level source directory, all files derived by
-configure are removed, so you see only the file contained in the source
-distribution.<P>
-
-<H3><a name="12">12</a>) How do I add a new port?</H3><P>
-
-There are a variety of places that need to be modified to add a new
-port. First, start in the <I>src/template</I> directory. Add an
-appropriate entry for your OS. Also, use <I>src/config.guess</I> to add
-your OS to <I>src/template/.similar.</I> You shouldn't match the OS
-version exactly. The <I>configure</I> test will look for an exact OS
-version number, and if not found, find a match without version number.
-Edit <I>src/configure.in</I> to add your new OS. (See configure item
-above.) You will need to run autoconf, or patch <I>src/configure</I>
-too.<P>
-
-Then, check <I>src/include/port</I> and add your new OS file, with
-appropriate values. Hopefully, there is already locking code in
-<I>src/include/storage/s_lock.h</I> for your CPU. There is also a
-<I>src/makefiles</I> directory for port-specific Makefile handling.
-There is a <I>backend/port</I> directory if you need special files for
-your OS.<P>
-
-
-</BODY>
-</HTML>
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