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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2//EN"> <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2//EN">
<html>
<head>
<meta name="generator" content=
"HTML Tidy for BSD/OS (vers 1st July 2002), see www.w3.org">
<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: Wed Dec 1 16:11:11 EST 2006</p>
<p>Current maintainer: Bruce Momjian (<a href=
"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</a>)<br>
</p>
<p>The most recent version of this document can be viewed at <a
href=
"http://www.PostgreSQL.org/docs/faqs/FAQ_DEV.html">http://www.PostgreSQL.org/docs/faqs/FAQ_DEV.html</a>.</p>
<hr>
<br>
<center>
<h2>General Questions</h2>
</center>
<a href="#1.1">1.1</a>) How do I get involved in PostgreSQL
development?<br>
<a href="#1.2">1.2</a>) What development environment is required
to develop code?<br>
<a href="#1.3">1.3</a>) What areas need work?<br>
<a href="#1.4">1.4</a>) What do I do after choosing an item to
work on?<br>
<a href="#1.5">1.5</a>) Where can I learn more about the code?<br>
<a href="#1.6">1.6</a>) I've developed a patch, what next?<br>
<a href="#1.7">1.7</a>) How do I download/update the current
source tree?<br>
<a href="#1.8">1.8</a>) How do I test my changes?<br>
<a href="#1.9">1.9</a>) What tools are available for
developers?<br>
<a href="#1.10">1.10</a>) What books are good for developers?<br>
<a href="#1.11">1.11</a>) What is configure all about?<br>
<a href="#1.12">1.12</a>) How do I add a new port?<br>
<a href="#1.13">1.13</a>) Why don't you use threads/raw
devices/async-I/O, &lt;insert your favorite wizz-bang feature
here&gt;?<br>
<a href="#1.14">1.14</a>) How are RPM's packaged?<br>
<a href="#1.15">1.15</a>) How are CVS branches handled?<br>
<a href="#1.16">1.16</a>) Where can I get a copy of the SQL
standards?<br>
<a href="#1.17">1.17</a>) Where can I get technical
assistance?<br>
<a href="#1.18">1.18</a>) How do I get involved in PostgreSQL web
site development?<br>
<center>
<h2>Technical Questions</h2>
</center>
<a href="#2.1">2.1</a>) How do I efficiently access information in
tables from the backend code?<br>
<a href="#2.2">2.2</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="#2.3">2.3</a>) Why do we use <i>Node</i> and <i>List</i>
to make data structures?<br>
<a href="#2.4">2.4</a>) I just added a field to a structure. What
else should I do?<br>
<a href="#2.5">2.5</a>) Why do we use <i>palloc</i>() and
<i>pfree</i>() to allocate memory?<br>
<a href="#2.6">2.6</a>) What is ereport()?<br>
<a href="#2.7">2.7</a>) What is CommandCounterIncrement()?<br>
<br>
<hr>
<center>
<h2>General Questions</h2>
</center>
<h3><a name="1.1">1.1</a>) How go I get involved in PostgreSQL
development?</h3>
<p>Download the code and have a look around. See <a href=
"#1.7">1.7</a>.</p>
<p>Subscribe to and read the <a href=
"http://archives.posrgresql.org/pgsql-hackers">pgsql-hackers</a>
mailing list (often termed 'hackers'). This is where the major
contributors and core members of the project discuss
development.</p>
<h3><a name="1.2">1.2</a>) What development environment is required
to develop code?</h3>
<p>PostgreSQL is developed mostly in the C programming language. It
also makes use of Yacc and Lex.</p>
<p>The source code is targeted at most of the popular Unix
platforms and the Windows environment (XP, Windows 2000, and
up).</p>
<p>Most developers make use of the open source development tool
chain. If you have contributed to open source software before, you
will probably be familiar with these tools. They include: GCC (<a
href="http://gcc.gnu.org">http://gcc.gnu.org</a>, GDB (<a href=
"http://www.gnu.org/software/gdb/gdb.html">www.gnu.org/software/gdb/gdb.html</a>),
autoconf (<a href=
"http://www.gnu.org/software/autoconf/">www.gnu.org/software/autoconf/</a>)
AND GNU make (<a href=
"http://www.gnu.org/software/make/make.html">www.gnu.org/software/make/make.html</a>.</p>
<p>Developers using this tool chain on Windows make use of MingW
(see <a href=
"http://www.mingw.org/">http://www.mingw.org/</a>).</p>
<p>Some developers use compilers from other software vendors with
mixed results.</p>
<p>Developers who are regularly rebuilding the source often pass
the --enable-depend flag to <i>configure</i>. The result is that
when you make a modification to a C header file, all files depend
upon that file are also rebuilt.</p>
<h3><a name="1.3">1.3</a>) What areas need work?</h3>
Outstanding features are detailed in the TODO list. This is located
in <i>doc/TODO</i> in the source distribution or at <a href=
"http://developer.postgresql.org/todo.php">http://developer.postgresql.org/todo.php</a>.
<p>You can learn more about these features by consulting the
archives, the SQL standards and the recommend texts (see <a href=
"#1.10">1.10</a>).</p>
<h3><a name="1.4">1.4</a>) What do I do after choosing an item to
work on?</h3>
<p>Send an email to pgsql-hackers with a proposal for what you want
to do (assuming your contribution is not trivial). Working in
isolation is not advisable: others may be working on the same TODO
item; you may have misunderstood the TODO item; your approach may
benefit from the review of others.</p>
<h3><a name="1.5">1.5</a>) Where can I learn more about the
code?</h3>
<p>Other than documentation in the source tree itself, you can find
some papers/presentations discussing the code at <a href=
"http://developers.postgresql.org">http://developers.postgresql.org</a>.</p>
<h3><a name="1.6">1.6</a>) I've developed a patch, what next?</h3>
<p>Generate the patch in contextual diff format. If you are
unfamiliar with this, you may find the script
<i>src/tools/makediff/difforig</i> useful.</p>
<p>Ensure that your patch is generated against the most recent
version of the code. If it is a patch adding new functionality, the
most recent version is cvs HEAD; if it is a bug fix, this will be
the most recently version of the branch which suffers from the bug
(for more on branches in PostgreSQL, see <a href=
"#1.15">1.15</a>).</p>
<p>Finally, submit the patch to pgsql-patches@postgresql.org. It
will be reviewed by other contributors to the project and may be
either accepted or sent back for further work.</p>
<h3><a name="1.7">1.7</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
<a href=
"ftp://ftp.postgresql.org">ftp://ftp.postgresql.org</a>.</p>
<p>Regular developers may want to take advantage of anonymous <HTML>
access to our source code management system. The source tree is <HEAD>
currently hosted in CVS. For details of how to obtain the source <META name="generator" content=
from CVS see <a href= "HTML Tidy for BSD/OS (vers 1st July 2002), see www.w3.org">
"http://developer.postgresql.org/docs/postgres/cvs.html">http://developer.postgresql.org/docs/postgres/cvs.html</a>.</p>
<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: Wed Dec 1 16:11:11 EST 2006</P>
<P>Current maintainer: Bruce Momjian (<A href=
"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR>
</P>
<P>The most recent version of this document can be viewed at <A
href=
"http://www.PostgreSQL.org/docs/faqs/FAQ_DEV.html">http://www.PostgreSQL.org/docs/faqs/FAQ_DEV.html</A>.</P>
<HR>
<BR>
<CENTER>
<H2>General Questions</H2>
</CENTER>
<A href="#1.1">1.1</A>) How do I get involved in PostgreSQL
development?<BR>
<A href="#1.2">1.2</A>) What development environment is required
to develop code?<BR>
<A href="#1.3">1.3</A>) What areas need work?<BR>
<A href="#1.4">1.4</A>) What do I do after choosing an item to
work on?<BR>
<A href="#1.5">1.5</A>) Where can I learn more about the code?<BR>
<A href="#1.6">1.6</A>) I've developed a patch, what next?<BR>
<A href="#1.7">1.7</A>) How do I download/update the current
source tree?<BR>
<A href="#1.8">1.8</A>) How do I test my changes?<BR>
<A href="#1.9">1.9</A>) What tools are available for
developers?<BR>
<A href="#1.10">1.10</A>) What books are good for developers?<BR>
<A href="#1.11">1.11</A>) What is configure all about?<BR>
<A href="#1.12">1.12</A>) How do I add a new port?<BR>
<A href="#1.13">1.13</A>) Why don't you use threads/raw
devices/async-I/O, &lt;insert your favorite wizz-bang feature
here&gt;?<BR>
<A href="#1.14">1.14</A>) How are RPM's packaged?<BR>
<A href="#1.15">1.15</A>) How are CVS branches handled?<BR>
<A href="#1.16">1.16</A>) Where can I get a copy of the SQL
standards?<BR>
<A href="#1.17">1.17</A>) Where can I get technical
assistance?<BR>
<A href="#1.18">1.18</A>) How do I get involved in PostgreSQL web
site development?<BR>
<CENTER>
<H2>Technical Questions</H2>
</CENTER>
<A href="#2.1">2.1</A>) How do I efficiently access information in
tables from the backend code?<BR>
<A href="#2.2">2.2</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="#2.3">2.3</A>) Why do we use <I>Node</I> and <I>List</I>
to make data structures?<BR>
<A href="#2.4">2.4</A>) I just added a field to a structure. What
else should I do?<BR>
<A href="#2.5">2.5</A>) Why do we use <I>palloc</I>() and
<I>pfree</I>() to allocate memory?<BR>
<A href="#2.6">2.6</A>) What is ereport()?<BR>
<A href="#2.7">2.7</A>) What is CommandCounterIncrement()?<BR>
<BR>
<HR>
<CENTER>
<H2>General Questions</H2>
</CENTER>
<H3><A name="1.1">1.1</A>) How go I get involved in PostgreSQL
development?</H3>
<P>Download the code and have a look around. See <A href=
"#1.7">1.7</A>.</P>
<P>Subscribe to and read the <A href=
"http://archives.posrgresql.org/pgsql-hackers">pgsql-hackers</A>
mailing list (often termed 'hackers'). This is where the major
contributors and core members of the project discuss
development.</P>
<H3><A name="1.2">1.2</A>) What development environment is required
to develop code?</H3>
<P>PostgreSQL is developed mostly in the C programming language. It
also makes use of Yacc and Lex.</P>
<P>The source code is targeted at most of the popular Unix
platforms and the Windows environment (XP, Windows 2000, and
up).</P>
<P>Most developers make use of the open source development tool
chain. If you have contributed to open source software before, you
will probably be familiar with these tools. They include: GCC (<A
href="http://gcc.gnu.org">http://gcc.gnu.org</A>, GDB (<A href=
"http://www.gnu.org/software/gdb/gdb.html">www.gnu.org/software/gdb/gdb.html</A>),
autoconf (<A href=
"http://www.gnu.org/software/autoconf/">www.gnu.org/software/autoconf/</A>)
AND GNU make (<A href=
"http://www.gnu.org/software/make/make.html">www.gnu.org/software/make/make.html</A>.</P>
<P>Developers using this tool chain on Windows make use of MingW
(see <A href=
"http://www.mingw.org/">http://www.mingw.org/</A>).</P>
<P>Some developers use compilers from other software vendors with
mixed results.</P>
<P>Developers who are regularly rebuilding the source often pass
the --enable-depend flag to <I>configure</I>. The result is that
when you make a modification to a C header file, all files depend
upon that file are also rebuilt.</P>
<H3><A name="1.3">1.3</A>) What areas need work?</H3>
Outstanding features are detailed in the TODO list. This is located
in <I>doc/TODO</I> in the source distribution or at <A href=
"http://developer.postgresql.org/todo.php">http://developer.postgresql.org/todo.php</A>.
<P>You can learn more about these features by consulting the
archives, the SQL standards and the recommend texts (see <A href=
"#1.10">1.10</A>).</P>
<H3><A name="1.4">1.4</A>) What do I do after choosing an item to
work on?</H3>
<P>Send an email to pgsql-hackers with a proposal for what you want
to do (assuming your contribution is not trivial). Working in
isolation is not advisable: others may be working on the same TODO
item; you may have misunderstood the TODO item; your approach may
benefit from the review of others.</P>
<H3><A name="1.5">1.5</A>) Where can I learn more about the
code?</H3>
<P>Other than documentation in the source tree itself, you can find
some papers/presentations discussing the code at <A href=
"http://developers.postgresql.org">http://developers.postgresql.org</A>.</P>
<H3><A name="1.6">1.6</A>) I've developed a patch, what next?</H3>
<P>Generate the patch in contextual diff format. If you are
unfamiliar with this, you may find the script
<I>src/tools/makediff/difforig</I> useful.</P>
<P>Ensure that your patch is generated against the most recent
version of the code. If it is a patch adding new functionality, the
most recent version is cvs HEAD; if it is a bug fix, this will be
the most recently version of the branch which suffers from the bug
(for more on branches in PostgreSQL, see <A href=
"#1.15">1.15</A>).</P>
<P>Finally, submit the patch to pgsql-patches@postgresql.org. It
will be reviewed by other contributors to the project and may be
either accepted or sent back for further work.</P>
<h3><a name="1.8">1.8</a>) How do I test my changes?</h3> <H3><A name="1.7">1.7</A>) How do I download/update the current
source tree?</H3>
<p><b>Basic system testing</b></p> <P>There are several ways to obtain the source tree. Occasional
developers can just get the most recent source tree snapshot from
<A href=
"ftp://ftp.postgresql.org">ftp://ftp.postgresql.org</A>.</P>
<p>The easiest way to test your code is to ensure that it builds <P>Regular developers may want to take advantage of anonymous
against the latest verion of the code and that it does not generate access to our source code management system. The source tree is
compiler warnings.</p> currently hosted in CVS. For details of how to obtain the source
from CVS see <A href=
"http://developer.postgresql.org/docs/postgres/cvs.html">http://developer.postgresql.org/docs/postgres/cvs.html</A>.</P>
<p>It is worth advised that you pass --enable-cassert to <H3><A name="1.8">1.8</A>) How do I test my changes?</H3>
<i>configure</i>. This will turn on assertions with in the source
which will often show us bugs because they cause data corruption of
segmentation violations. This generally makes debugging much
easier.</p>
<p>Then, perform run time testing via psql.</p> <P><B>Basic system testing</B></P>
<p><b>Regression test suite</b></p> <P>The easiest way to test your code is to ensure that it builds
against the latest verion of the code and that it does not generate
compiler warnings.</P>
<p>The next step is to test your changes against the existing <P>It is worth advised that you pass --enable-cassert to
regression test suite. To do this, issue "make check" in the root <I>configure</I>. This will turn on assertions with in the source
directory of the source tree. If any tests failure, which will often show us bugs because they cause data corruption of
investigate.</p> segmentation violations. This generally makes debugging much
easier.</P>
<p>If you've deliberately changed existing behaviour, this change <P>Then, perform run time testing via psql.</P>
may cause a regression test failure but not any actual regression.
If so, you should also patch the regression test suite.</p>
<p><b>Other run time testing</b></p> <P><B>Regression test suite</B></P>
<p>Some developers make use of tools such as valgrind (<a href= <P>The next step is to test your changes against the existing
"http://valgrind.kde.org">http://valgrind.kde.org</a>) for memory regression test suite. To do this, issue "make check" in the root
testing, gprof (which comes with the GNU binutils suite) and directory of the source tree. If any tests failure,
oprofile (<a href= investigate.</P>
"http://oprofile.sourceforge.net/">http://oprofile.sourceforge.net/</a>)
for profiling and other related tools.</p>
<p><b>What about unit testing, static analysis, model <P>If you've deliberately changed existing behaviour, this change
checking...?</b></p> may cause a regression test failure but not any actual regression.
If so, you should also patch the regression test suite.</P>
<p>There have been a number of discussions about other testing <P><B>Other run time testing</B></P>
frameworks and some developers are exploring these ideas.</p>
<h3><a name="1.9">1.9</a>) What tools are available for <P>Some developers make use of tools such as valgrind (<A href=
developers?</h3> "http://valgrind.kde.org">http://valgrind.kde.org</A>) for memory
testing, gprof (which comes with the GNU binutils suite) and
oprofile (<A href=
"http://oprofile.sourceforge.net/">http://oprofile.sourceforge.net/</A>)
for profiling and other related tools.</P>
<p>First, all the files in the <i>src/tools</i> directory are <P><B>What about unit testing, static analysis, model
designed for developers.</p> checking...?</B></P>
<pre> <P>There have been a number of discussions about other testing
frameworks and some developers are exploring these ideas.</P>
<H3><A name="1.9">1.9</A>) What tools are available for
developers?</H3>
<P>First, all the files in the <I>src/tools</I> directory are
designed for developers.</P>
<PRE>
RELEASE_CHANGES changes we have to make for each release RELEASE_CHANGES changes we have to make for each release
backend description/flowchart of the backend directories backend description/flowchart of the backend directories
ccsym find standard defines made by your compiler ccsym find standard defines made by your compiler
...@@ -251,54 +253,52 @@ designed for developers.</p> ...@@ -251,54 +253,52 @@ designed for developers.</p>
pgindent indents source files pgindent indents source files
pgtest a semi-automated build system pgtest a semi-automated build system
thread a thread testing script thread a thread testing script
</pre> </PRE>
<p>In <i>src/include/catalog</i>:</p>
<pre> <P>In <I>src/include/catalog</I>:</P>
<PRE>
unused_oids a script which generates unused OIDs for use in system unused_oids a script which generates unused OIDs for use in system
catalogs catalogs
duplicate_oids finds duplicate OIDs in system catalog definitions duplicate_oids finds duplicate OIDs in system catalog definitions
</pre> </PRE>
If you point your browser at the <I>tools/backend/index.html</I>
If you point your browser at the <i>tools/backend/index.html</i> file, you will see few paragraphs describing the data flow, the
file, you will see few paragraphs describing the data flow, the backend components in a flow chart, and a description of the shared
backend components in a flow chart, and a description of the shared memory area. You can click on any flowchart box to see a
memory area. You can click on any flowchart box to see a description. If you then click on the directory name, you will be
description. If you then click on the directory name, you will be taken to the source directory, to browse the actual source code
taken to the source directory, to browse the actual source code behind it. We also have several README files in some source
behind it. We also have several README files in some source directories to describe the function of the module. The browser
directories to describe the function of the module. The browser will display these when you enter the directory also. The
will display these when you enter the directory also. The <I>tools/backend</I> directory is also contained on our web page
<i>tools/backend</i> directory is also contained on our web page under the title <I>How PostgreSQL Processes a Query.</I>
under the title <i>How PostgreSQL Processes a Query.</i>
<p>Second, you really should have an editor that can handle tags, <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 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, then tag inside that function to see an even lower-level function,
and then back out twice to return to the original function. Most 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> editors support this via <I>tags</I> or <I>etags</I> files.</P>
<p>Third, you need to get <i>id-utils</i> from <a href= <P>Third, you need to get <I>id-utils</I> from <A href=
"ftp://ftp.gnu.org/gnu/id-utils/">ftp://ftp.gnu.org/gnu/id-utils/</a></p> "ftp://ftp.gnu.org/gnu/id-utils/">ftp://ftp.gnu.org/gnu/id-utils/</A></P>
<p>By running <i>tools/make_mkid</i>, an archive of source symbols <P>By running <I>tools/make_mkid</I>, an archive of source symbols
can be created that can be rapidly queried.</p> can be created that can be rapidly queried.</P>
<p>Some developers make use of cscope, which can be found at <a <P>Some developers make use of cscope, which can be found at <A
href="http://cscope.sf.net">http://cscope.sf.net/</a>. Others use href="http://cscope.sf.net">http://cscope.sf.net/</A>. Others use
glimpse, which can be found at <a href= glimpse, which can be found at <A href=
"http://webglimpse.net/">http://webglimpse.net/</a>.</p> "http://webglimpse.net/">http://webglimpse.net/</A>.</P>
<p><i>tools/make_diff</i> has tools to create patch diff files that <P><I>tools/make_diff</I> has tools to create patch diff files that
can be applied to the distribution. This produces context diffs, can be applied to the distribution. This produces context diffs,
which is our preferred format.</p> which is our preferred format.</P>
<p>Our standard format is to indent each code level with one tab, <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 where each tab is four spaces. You will need to set your editor to
display tabs as four spaces:<br> display tabs as four spaces:<BR>
</p> </P>
<PRE>
<pre>
vi in ~/.exrc: vi in ~/.exrc:
set tabstop=4 set tabstop=4
set sw=4 set sw=4
...@@ -339,497 +339,492 @@ display tabs as four spaces:<br> ...@@ -339,497 +339,492 @@ display tabs as four spaces:<br>
* c-basic-offset: 4 * c-basic-offset: 4
* End: * End:
*/ */
</pre> </PRE>
<BR>
<br> <I>pgindent</I> will the format code by specifying flags to your
<i>pgindent</i> will the format code by specifying flags to your operating system's utility <I>indent.</I> This <A href=
operating system's utility <i>indent.</i> This <a href= "http://ezine.daemonnews.org/200112/single_coding_style.html">article</A>
"http://ezine.daemonnews.org/200112/single_coding_style.html">article</a> describes the value of a consistent coding style.
describes the value of a consistent coding style.
<p><i>pgindent</i> is run on all source files just before each beta <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 test period. It auto-formats all source files to make them
consistent. Comment blocks that need specific line breaks should be consistent. Comment blocks that need specific line breaks should be
formatted as <i>block comments,</i> where the comment starts as formatted as <I>block comments,</I> where the comment starts as
<code>/*------</code>. These comments will not be reformatted in <CODE>/*------</CODE>. These comments will not be reformatted in
any way.</p> any way.</P>
<p><i>pginclude</i> contains scripts used to add needed <P><I>pginclude</I> contains scripts used to add needed
<code>#include</code>'s to include files, and removed unneeded <CODE>#include</CODE>'s to include files, and removed unneeded
<code>#include</code>'s.</p> <CODE>#include</CODE>'s.</P>
<p>When adding system types, you will need to assign oids to them. <P>When adding system types, you will need to assign oids to them.
There is also a script called <i>unused_oids</i> in There is also a script called <I>unused_oids</I> in
<i>pgsql/src/include/catalog</i> that shows the unused oids.</p> <I>pgsql/src/include/catalog</I> that shows the unused oids.</P>
<h3><a name="1.10">1.10</a>) What books are good for <H3><A name="1.10">1.10</A>) What books are good for
developers?</h3> developers?</H3>
<p>I have four good books, <i>An Introduction to Database <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 Systems,</I> by C.J. Date, Addison, Wesley, <I>A Guide to the SQL
Standard,</i> by C.J. Date, et. al, Addison, Wesley, Standard,</I> by C.J. Date, et. al, Addison, Wesley,
<i>Fundamentals of Database Systems,</i> by Elmasri and Navathe, <I>Fundamentals of Database Systems,</I> by Elmasri and Navathe,
and <i>Transaction Processing,</i> by Jim Gray, Morgan, and <I>Transaction Processing,</I> by Jim Gray, Morgan,
Kaufmann</p> Kaufmann</P>
<p>There is also a database performance site, with a handbook <P>There is also a database performance site, with a handbook
on-line written by Jim Gray at <a href= on-line written by Jim Gray at <A href=
"http://www.benchmarkresources.com">http://www.benchmarkresources.com.</a>.</p> "http://www.benchmarkresources.com">http://www.benchmarkresources.com.</A>.</P>
<h3><a name="1.11">1.11</a>) What is configure all about?</h3> <H3><A name="1.11">1.11</A>) What is configure all about?</H3>
<p>The files <i>configure</i> and <i>configure.in</i> are part of <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 the GNU <I>autoconf</I> package. Configure allows us to test for
various capabilities of the OS, and to set variables that can then various capabilities of the OS, and to set variables that can then
be tested in C programs and Makefiles. Autoconf is installed on the be tested in C programs and Makefiles. Autoconf is installed on the
PostgreSQL main server. To add options to configure, edit PostgreSQL main server. To add options to configure, edit
<i>configure.in,</i> and then run <i>autoconf</i> to generate <I>configure.in,</I> and then run <I>autoconf</I> to generate
<i>configure.</i></p> <I>configure.</I></P>
<p>When <i>configure</i> is run by the user, it tests various OS <P>When <I>configure</I> is run by the user, it tests various OS
capabilities, stores those in <i>config.status</i> and capabilities, stores those in <I>config.status</I> and
<i>config.cache,</i> and modifies a list of <i>*.in</i> files. For <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 example, if there exists a <I>Makefile.in,</I> configure generates
a <i>Makefile</i> that contains substitutions for all @var@ a <I>Makefile</I> that contains substitutions for all @var@
parameters found by configure.</p> parameters found by configure.</P>
<p>When you need to edit files, make sure you don't waste time <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> 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 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, you run <I>make distclean</I> from the top-level source directory,
all files derived by configure are removed, so you see only the all files derived by configure are removed, so you see only the
file contained in the source distribution.</p> file contained in the source distribution.</P>
<h3><a name="1.12">1.12</a>) How do I add a new port?</h3> <H3><A name="1.12">1.12</A>) How do I add a new port?</H3>
<p>There are a variety of places that need to be modified to add a <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 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 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 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 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 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. 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 (See configure item above.) You will need to run autoconf, or patch
<i>src/configure</i> too.</p> <I>src/configure</I> too.</P>
<p>Then, check <i>src/include/port</i> and add your new OS file, <P>Then, check <I>src/include/port</I> and add your new OS file,
with appropriate values. Hopefully, there is already locking code with appropriate values. Hopefully, there is already locking code
in <i>src/include/storage/s_lock.h</i> for your CPU. There is also 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 a <I>src/makefiles</I> directory for port-specific Makefile
handling. There is a <i>backend/port</i> directory if you need handling. There is a <I>backend/port</I> directory if you need
special files for your OS.</p> special files for your OS.</P>
<h3><a name="1.13">1.13</a>) Why don't you use threads/raw <H3><A name="1.13">1.13</A>) Why don't you use threads/raw
devices/async-I/O, &lt;insert your favorite wizz-bang feature devices/async-I/O, &lt;insert your favorite wizz-bang feature
here&gt;?</h3> here&gt;?</H3>
<p>There is always a temptation to use the newest operating system <P>There is always a temptation to use the newest operating system
features as soon as they arrive. We resist that temptation.</p> features as soon as they arrive. We resist that temptation.</P>
<p>First, we support 15+ operating systems, so any new feature has <P>First, we support 15+ operating systems, so any new feature has
to be well established before we will consider it. Second, most new to be well established before we will consider it. Second, most new
<i>wizz-bang</i> features don't provide <i>dramatic</i> <I>wizz-bang</I> features don't provide <I>dramatic</I>
improvements. Third, they usually have some downside, such as improvements. Third, they usually have some downside, such as
decreased reliability or additional code required. Therefore, we decreased reliability or additional code required. Therefore, we
don't rush to use new features but rather wait for the feature to don't rush to use new features but rather wait for the feature to
be established, then ask for testing to show that a measurable be established, then ask for testing to show that a measurable
improvement is possible.</p> improvement is possible.</P>
<p>As an example, threads are not currently used in the backend <P>As an example, threads are not currently used in the backend
code because:</p> code because:</P>
<ul> <UL>
<li>Historically, threads were unsupported and buggy.</li> <LI>Historically, threads were unsupported and buggy.</LI>
<li>An error in one backend can corrupt other backends.</li> <LI>An error in one backend can corrupt other backends.</LI>
<li>Speed improvements using threads are small compared to the <LI>Speed improvements using threads are small compared to the
remaining backend startup time.</li> remaining backend startup time.</LI>
<li>The backend code would be more complex.</li> <LI>The backend code would be more complex.</LI>
</ul> </UL>
<p>So, we are not ignorant of new features. It is just that we are <P>So, we are not ignorant of new features. It is just that we are
cautious about their adoption. The TODO list often contains links cautious about their adoption. The TODO list often contains links
to discussions showing our reasoning in these areas.</p> to discussions showing our reasoning in these areas.</P>
<h3><a name="1.14">1.14</a>) How are RPMs packaged?</h3> <H3><A name="1.14">1.14</A>) How are RPMs packaged?</H3>
<p>This was written by Lamar Owen:</p> <P>This was written by Lamar Owen:</P>
<p>2001-05-03</p> <P>2001-05-03</P>
<p>As to how the RPMs are built -- to answer that question sanely <P>As to how the RPMs are built -- to answer that question sanely
requires me to know how much experience you have with the whole RPM requires me to know how much experience you have with the whole RPM
paradigm. 'How is the RPM built?' is a multifaceted question. The paradigm. 'How is the RPM built?' is a multifaceted question. The
obvious simple answer is that I maintain:</p> obvious simple answer is that I maintain:</P>
<ol> <OL>
<li>A set of patches to make certain portions of the source tree <LI>A set of patches to make certain portions of the source tree
'behave' in the different environment of the RPMset;</li> 'behave' in the different environment of the RPMset;</LI>
<li>The initscript;</li> <LI>The initscript;</LI>
<li>Any other ancilliary scripts and files;</li> <LI>Any other ancilliary scripts and files;</LI>
<li>A README.rpm-dist document that tries to adequately document <LI>A README.rpm-dist document that tries to adequately document
both the differences between the RPM build and the WHY of the both the differences between the RPM build and the WHY of the
differences, as well as useful RPM environment operations (like, differences, as well as useful RPM environment operations (like,
using syslog, upgrading, getting postmaster to start at OS boot, using syslog, upgrading, getting postmaster to start at OS boot,
etc);</li> etc);</LI>
<li>The spec file that throws it all together. This is not a <LI>The spec file that throws it all together. This is not a
trivial undertaking in a package of this size.</li> trivial undertaking in a package of this size.</LI>
</ol> </OL>
<p>I then download and build on as many different canonical <P>I then download and build on as many different canonical
distributions as I can -- currently I am able to build on Red Hat distributions as I can -- currently I am able to build on Red Hat
6.2, 7.0, and 7.1 on my personal hardware. Occasionally I receive 6.2, 7.0, and 7.1 on my personal hardware. Occasionally I receive
opportunity from certain commercial enterprises such as Great opportunity from certain commercial enterprises such as Great
Bridge and PostgreSQL, Inc. to build on other distributions.</p> Bridge and PostgreSQL, Inc. to build on other distributions.</P>
<p>I test the build by installing the resulting packages and <P>I test the build by installing the resulting packages and
running the regression tests. Once the build passes these tests, I running the regression tests. Once the build passes these tests, I
upload to the postgresql.org ftp server and make a release upload to the postgresql.org ftp server and make a release
announcement. I am also responsible for maintaining the RPM announcement. I am also responsible for maintaining the RPM
download area on the ftp site.</p> download area on the ftp site.</P>
<p>You'll notice I said 'canonical' distributions above. That <P>You'll notice I said 'canonical' distributions above. That
simply means that the machine is as stock 'out of the box' as simply means that the machine is as stock 'out of the box' as
practical -- that is, everything (except select few programs) on practical -- that is, everything (except select few programs) on
these boxen are installed by RPM; only official Red Hat released these boxen are installed by RPM; only official Red Hat released
RPMs are used (except in unusual circumstances involving software RPMs are used (except in unusual circumstances involving software
that will not alter the build -- for example, installing a newer that will not alter the build -- for example, installing a newer
non-RedHat version of the Dia diagramming package is OK -- non-RedHat version of the Dia diagramming package is OK --
installing Python 2.1 on the box that has Python 1.5.2 installed is installing Python 2.1 on the box that has Python 1.5.2 installed is
not, as that alters the PostgreSQL build). The RPM as uploaded is not, as that alters the PostgreSQL build). The RPM as uploaded is
built to as close to out-of-the-box pristine as is possible. Only built to as close to out-of-the-box pristine as is possible. Only
the standard released 'official to that release' compiler is used the standard released 'official to that release' compiler is used
-- and only the standard official kernel is used as well.</p> -- and only the standard official kernel is used as well.</P>
<p>For a time I built on Mandrake for RedHat consumption -- no <P>For a time I built on Mandrake for RedHat consumption -- no
more. Nonstandard RPM building systems are worse than useless. more. Nonstandard RPM building systems are worse than useless.
Which is not to say that Mandrake is useless! By no means is Which is not to say that Mandrake is useless! By no means is
Mandrake useless -- unless you are building Red Hat RPMs -- and Red Mandrake useless -- unless you are building Red Hat RPMs -- and Red
Hat is useless if you're trying to build Mandrake or SuSE RPMs, for Hat is useless if you're trying to build Mandrake or SuSE RPMs, for
that matter. But I would be foolish to use 'Lamar Owen's Super that matter. But I would be foolish to use 'Lamar Owen's Super
Special RPM Blend Distro 0.1.2' to build for public consumption! Special RPM Blend Distro 0.1.2' to build for public consumption!
:-)</p> :-)</P>
<p>I _do_ attempt to make the _source_ RPM compatible with as many <P>I _do_ attempt to make the _source_ RPM compatible with as many
distributions as possible -- however, since I have limited distributions as possible -- however, since I have limited
resources (as a volunteer RPM maintainer) I am limited as to the resources (as a volunteer RPM maintainer) I am limited as to the
amount of testing said build will get on other distributions, amount of testing said build will get on other distributions,
architectures, or systems.</p> architectures, or systems.</P>
<p>And, while I understand people's desire to immediately upgrade <P>And, while I understand people's desire to immediately upgrade
to the newest version, realize that I do this as a side interest -- to the newest version, realize that I do this as a side interest --
I have a regular, full-time job as a broadcast I have a regular, full-time job as a broadcast
engineer/webmaster/sysadmin/Technical Director which occasionally engineer/webmaster/sysadmin/Technical Director which occasionally
prevents me from making timely RPM releases. This happened during prevents me from making timely RPM releases. This happened during
the early part of the 7.1 beta cycle -- but I believe I was pretty the early part of the 7.1 beta cycle -- but I believe I was pretty
much on the ball for the Release Candidates and the final much on the ball for the Release Candidates and the final
release.</p> release.</P>
<p>I am working towards a more open RPM distribution -- I would <P>I am working towards a more open RPM distribution -- I would
dearly love to more fully document the process and put everything dearly love to more fully document the process and put everything
into CVS -- once I figure out how I want to represent things such into CVS -- once I figure out how I want to represent things such
as the spec file in a CVS form. It makes no sense to maintain a as the spec file in a CVS form. It makes no sense to maintain a
changelog, for instance, in the spec file in CVS when CVS does a changelog, for instance, in the spec file in CVS when CVS does a
better job of changelogs -- I will need to write a tool to generate better job of changelogs -- I will need to write a tool to generate
a real spec file from a CVS spec-source file that would add version a real spec file from a CVS spec-source file that would add version
numbers, changelog entries, etc to the result before building the numbers, changelog entries, etc to the result before building the
RPM. IOW, I need to rethink the process -- and then go through the RPM. IOW, I need to rethink the process -- and then go through the
motions of putting my long RPM history into CVS one version at a motions of putting my long RPM history into CVS one version at a
time so that version history information isn't lost.</p> time so that version history information isn't lost.</P>
<p>As to why all these files aren't part of the source tree, well, <P>As to why all these files aren't part of the source tree, well,
unless there was a large cry for it to happen, I don't believe it unless there was a large cry for it to happen, I don't believe it
should. PostgreSQL is very platform-agnostic -- and I like that. should. PostgreSQL is very platform-agnostic -- and I like that.
Including the RPM stuff as part of the Official Tarball (TM) would, Including the RPM stuff as part of the Official Tarball (TM) would,
IMHO, slant that agnostic stance in a negative way. But maybe I'm IMHO, slant that agnostic stance in a negative way. But maybe I'm
too sensitive to that. I'm not opposed to doing that if that is the too sensitive to that. I'm not opposed to doing that if that is the
consensus of the core group -- and that would be a sneaky way to consensus of the core group -- and that would be a sneaky way to
get the stuff into CVS :-). But if the core group isn't thrilled get the stuff into CVS :-). But if the core group isn't thrilled
with the idea (and my instinct says they're not likely to be), I am with the idea (and my instinct says they're not likely to be), I am
opposed to the idea -- not to keep the stuff to myself, but to not opposed to the idea -- not to keep the stuff to myself, but to not
hinder the platform-neutral stance. IMHO, of course.</p> hinder the platform-neutral stance. IMHO, of course.</P>
<p>Of course, there are many projects that DO include all the files <P>Of course, there are many projects that DO include all the files
necessary to build RPMs from their Official Tarball (TM).</p> necessary to build RPMs from their Official Tarball (TM).</P>
<h3><a name="1.15">1.15</a>) How are CVS branches managed?</h3> <H3><A name="1.15">1.15</A>) How are CVS branches managed?</H3>
<p>This was written by Tom Lane:</p> <P>This was written by Tom Lane:</P>
<p>2001-05-07</p> <P>2001-05-07</P>
<p>If you just do basic "cvs checkout", "cvs update", "cvs commit", <P>If you just do basic "cvs checkout", "cvs update", "cvs commit",
then you'll always be dealing with the HEAD version of the files in then you'll always be dealing with the HEAD version of the files in
CVS. That's what you want for development, but if you need to patch CVS. That's what you want for development, but if you need to patch
past stable releases then you have to be able to access and update past stable releases then you have to be able to access and update
the "branch" portions of our CVS repository. We normally fork off a the "branch" portions of our CVS repository. We normally fork off a
branch for a stable release just before starting the development branch for a stable release just before starting the development
cycle for the next release.</p> cycle for the next release.</P>
<p>The first thing you have to know is the branch name for the <P>The first thing you have to know is the branch name for the
branch you are interested in getting at. To do this, look at some branch you are interested in getting at. To do this, look at some
long-lived file, say the top-level HISTORY file, with "cvs status long-lived file, say the top-level HISTORY file, with "cvs status
-v" to see what the branch names are. (Thanks to Ian Lance Taylor -v" to see what the branch names are. (Thanks to Ian Lance Taylor
for pointing out that this is the easiest way to do it.) Typical for pointing out that this is the easiest way to do it.) Typical
branch names are:</p> branch names are:</P>
<PRE>
<pre>
REL7_1_STABLE REL7_1_STABLE
REL7_0_PATCHES REL7_0_PATCHES
REL6_5_PATCHES REL6_5_PATCHES
</pre> </PRE>
<p>OK, so how do you do work on a branch? By far the best way is to <P>OK, so how do you do work on a branch? By far the best way is to
create a separate checkout tree for the branch and do your work in create a separate checkout tree for the branch and do your work in
that. Not only is that the easiest way to deal with CVS, but you that. Not only is that the easiest way to deal with CVS, but you
really need to have the whole past tree available anyway to test really need to have the whole past tree available anyway to test
your work. (And you *better* test your work. Never forget that your work. (And you *better* test your work. Never forget that
dot-releases tend to go out with very little beta testing --- so dot-releases tend to go out with very little beta testing --- so
whenever you commit an update to a stable branch, you'd better be whenever you commit an update to a stable branch, you'd better be
doubly sure that it's correct.)</p> doubly sure that it's correct.)</P>
<p>Normally, to checkout the head branch, you just cd to the place <P>Normally, to checkout the head branch, you just cd to the place
you want to contain the toplevel "pgsql" directory and say</p> you want to contain the toplevel "pgsql" directory and say</P>
<PRE>
<pre>
cvs ... checkout pgsql cvs ... checkout pgsql
</pre> </PRE>
<p>To get a past branch, you cd to whereever you want it and
say</p>
<pre> <P>To get a past branch, you cd to whereever you want it and
say</P>
<PRE>
cvs ... checkout -r BRANCHNAME pgsql cvs ... checkout -r BRANCHNAME pgsql
</pre> </PRE>
<p>For example, just a couple days ago I did</p>
<pre> <P>For example, just a couple days ago I did</P>
<PRE>
mkdir ~postgres/REL7_1 mkdir ~postgres/REL7_1
cd ~postgres/REL7_1 cd ~postgres/REL7_1
cvs ... checkout -r REL7_1_STABLE pgsql cvs ... checkout -r REL7_1_STABLE pgsql
</pre> </PRE>
<p>and now I have a maintenance copy of 7.1.*.</p> <P>and now I have a maintenance copy of 7.1.*.</P>
<p>When you've done a checkout in this way, the branch name is <P>When you've done a checkout in this way, the branch name is
"sticky": CVS automatically knows that this directory tree is for "sticky": CVS automatically knows that this directory tree is for
the branch, and whenever you do "cvs update" or "cvs commit" in the branch, and whenever you do "cvs update" or "cvs commit" in
this tree, you'll fetch or store the latest version in the branch, this tree, you'll fetch or store the latest version in the branch,
not the head version. Easy as can be.</p> not the head version. Easy as can be.</P>
<p>So, if you have a patch that needs to apply to both the head and <P>So, if you have a patch that needs to apply to both the head and
a recent stable branch, you have to make the edits and do the a recent stable branch, you have to make the edits and do the
commit twice, once in your development tree and once in your stable commit twice, once in your development tree and once in your stable
branch tree. This is kind of a pain, which is why we don't normally branch tree. This is kind of a pain, which is why we don't normally
fork the tree right away after a major release --- we wait for a fork the tree right away after a major release --- we wait for a
dot-release or two, so that we won't have to double-patch the first dot-release or two, so that we won't have to double-patch the first
wave of fixes.</p> wave of fixes.</P>
<h3><a name="1.16">1.16</a>) Where can I get a copy of the SQL <H3><A name="1.16">1.16</A>) Where can I get a copy of the SQL
standards?</h3> standards?</H3>
<p>There are three versions of the SQL standard: SQL-92, SQL:1999, <P>There are three versions of the SQL standard: SQL-92, SQL:1999,
and SQL:2003. They are endorsed by ANSI and ISO. Draft versions can and SQL:2003. They are endorsed by ANSI and ISO. Draft versions can
be downloaded from:</p> be downloaded from:</P>
<ul> <UL>
<li>SQL-92 <a href= <LI>SQL-92 <A href=
"http://www.contrib.andrew.cmu.edu/~shadow/sql/sql1992.txt">http://www.contrib.andrew.cmu.edu/~shadow/sql/sql1992.txt</a></li> "http://www.contrib.andrew.cmu.edu/~shadow/sql/sql1992.txt">http://www.contrib.andrew.cmu.edu/~shadow/sql/sql1992.txt</A></LI>
<li>SQL:1999 <a href= <LI>SQL:1999 <A href=
"http://www.cse.iitb.ac.in/dbms/Data/Papers-Other/SQL1999/ansi-iso-9075-2-1999.pdf"> "http://www.cse.iitb.ac.in/dbms/Data/Papers-Other/SQL1999/ansi-iso-9075-2-1999.pdf">
http://www.cse.iitb.ac.in/dbms/Data/Papers-Other/SQL1999/ansi-iso-9075-2-1999.pdf</a></li> http://www.cse.iitb.ac.in/dbms/Data/Papers-Other/SQL1999/ansi-iso-9075-2-1999.pdf</A></LI>
<li>SQL:2003 <a href= <LI>SQL:2003 <A href=
"http://www.wiscorp.com/sql/sql_2003_standard.zip">http://www.wiscorp.com/sql/sql_2003_standard.zip</a></li> "http://www.wiscorp.com/sql/sql_2003_standard.zip">http://www.wiscorp.com/sql/sql_2003_standard.zip</A></LI>
</ul> </UL>
<p>Some SQL standards web pages are:</p> <P>Some SQL standards web pages are:</P>
<ul> <UL>
<li><a href= <LI><A href=
"http://troels.arvin.dk/db/rdbms/links/#standards">http://troels.arvin.dk/db/rdbms/links/#standards</a></li> "http://troels.arvin.dk/db/rdbms/links/#standards">http://troels.arvin.dk/db/rdbms/links/#standards</A></LI>
<li><a href= <LI><A href=
"http://www.wiscorp.com/SQLStandards.html">http://www.wiscorp.com/SQLStandards.html</a></li> "http://www.wiscorp.com/SQLStandards.html">http://www.wiscorp.com/SQLStandards.html</A></LI>
<li><a href= <LI><A href=
"http://www.contrib.andrew.cmu.edu/~shadow/sql.html#syntax">http://www.contrib.andrew.cmu.edu/~shadow/sql.html#syntax</a> "http://www.contrib.andrew.cmu.edu/~shadow/sql.html#syntax">http://www.contrib.andrew.cmu.edu/~shadow/sql.html#syntax</A>
(SQL-92)</li> (SQL-92)</LI>
<li><a href= <LI><A href=
"http://dbs.uni-leipzig.de/en/lokal/standards.pdf">http://dbs.uni-leipzig.de/en/lokal/standards.pdf</a> "http://dbs.uni-leipzig.de/en/lokal/standards.pdf">http://dbs.uni-leipzig.de/en/lokal/standards.pdf</A>
(paper)</li> (paper)</LI>
</ul> </UL>
<h3><a name="1.17">1.17</a>) Where can I get technical <H3><A name="1.17">1.17</A>) Where can I get technical
assistance?</h3> assistance?</H3>
<p>Many technical questions held by those new to the code have been <P>Many technical questions held by those new to the code have been
answered on the pgsql-hackers mailing list - the archives of which answered on the pgsql-hackers mailing list - the archives of which
can be found at <a href= can be found at <A href=
"http://archives.postgresql.org/pgsql-hackers/">http://archives.postgresql.org/pgsql-hackers/</a>.</p> "http://archives.postgresql.org/pgsql-hackers/">http://archives.postgresql.org/pgsql-hackers/</A>.</P>
<p>If you cannot find discussion or your particular question, feel <P>If you cannot find discussion or your particular question, feel
free to put it to the list.</p> free to put it to the list.</P>
<p>Major contributors also answer technical questions, including <P>Major contributors also answer technical questions, including
questions about development of new features, on IRC at questions about development of new features, on IRC at
irc.freenode.net in the #postgresql channel.</p> irc.freenode.net in the #postgresql channel.</P>
<h3><a name="1.18">1.18</a>) How go I get involved in PostgreSQL <H3><A name="1.18">1.18</A>) How go I get involved in PostgreSQL
web site development?</h3> web site development?</H3>
<p>PostgreSQL website development is discussed on the <P>PostgreSQL website development is discussed on the
pgsql-www@postgresql.org mailing list. The is a project page where pgsql-www@postgresql.org mailing list. The is a project page where
the source code is available at <a href= the source code is available at <A href=
"http://gborg.postgresql.org/project/pgweb/projdisplay.php">http://gborg.postgresql.org/project/pgweb/projdisplay.php</a> "http://gborg.postgresql.org/project/pgweb/projdisplay.php">http://gborg.postgresql.org/project/pgweb/projdisplay.php</A>
, the code for the next version of the website is under the , the code for the next version of the website is under the
"portal" module. You will al so find code for the "techdocs" "portal" module. You will al so find code for the "techdocs"
website if you would like to contribute to that. A temporary todo website if you would like to contribute to that. A temporary todo
list for current website development issues is available at <a list for current website development issues is available at <A
href= href=
"http://xzilla.postgresql.org/todo">http://xzilla.postgresql.org/todo</a></p> "http://xzilla.postgresql.org/todo">http://xzilla.postgresql.org/todo</A></P>
<center> <CENTER>
<h2>Technical Questions</h2> <H2>Technical Questions</H2>
</center> </CENTER>
<h3><a name="2.1">2.1</a>) How do I efficiently access information <H3><A name="2.1">2.1</A>) How do I efficiently access information
in tables from the backend code?</h3> in tables from the backend code?</H3>
<p>You first need to find the tuples(rows) you are interested in. <P>You first need to find the tuples(rows) you are interested in.
There are two ways. First, <i>SearchSysCache()</i> and related There are two ways. First, <I>SearchSysCache()</I> and related
functions allow you to query the system catalogs. This is the functions allow you to query the system catalogs. This is the
preferred way to access system tables, because the first call to preferred way to access system tables, because the first call to
the cache loads the needed rows, and future requests can return the the cache loads the needed rows, and future requests can return the
results without accessing the base table. The caches use system results without accessing the base table. The caches use system
table indexes to look up tuples. A list of available caches is table indexes to look up tuples. A list of available caches is
located in <i>src/backend/utils/cache/syscache.c.</i> located in <I>src/backend/utils/cache/syscache.c.</I>
<i>src/backend/utils/cache/lsyscache.c</i> contains many <I>src/backend/utils/cache/lsyscache.c</I> contains many
column-specific cache lookup functions.</p> column-specific cache lookup functions.</P>
<p>The rows returned are cache-owned versions of the heap rows. <P>The rows returned are cache-owned versions of the heap rows.
Therefore, you must not modify or delete the tuple returned by Therefore, you must not modify or delete the tuple returned by
<i>SearchSysCache()</i>. What you <i>should</i> do is release it <I>SearchSysCache()</I>. What you <I>should</I> do is release it
with <i>ReleaseSysCache()</i> when you are done using it; this with <I>ReleaseSysCache()</I> when you are done using it; this
informs the cache that it can discard that tuple if necessary. If informs the cache that it can discard that tuple if necessary. If
you neglect to call <i>ReleaseSysCache()</i>, then the cache entry you neglect to call <I>ReleaseSysCache()</I>, then the cache entry
will remain locked in the cache until end of transaction, which is will remain locked in the cache until end of transaction, which is
tolerable but not very desirable.</p> tolerable but not very desirable.</P>
<p>If you can't use the system cache, you will need to retrieve the <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 data directly from the heap table, using the buffer cache that is
shared by all backends. The backend automatically takes care of shared by all backends. The backend automatically takes care of
loading the rows into the buffer cache.</p> loading the rows into the buffer cache.</P>
<p>Open the table with <i>heap_open().</i> You can then start a <P>Open the table with <I>heap_open().</I> You can then start a
table scan with <i>heap_beginscan(),</i> then use table scan with <I>heap_beginscan(),</I> then use
<i>heap_getnext()</i> and continue as long as <I>heap_getnext()</I> and continue as long as
<i>HeapTupleIsValid()</i> returns true. Then do a <I>HeapTupleIsValid()</I> returns true. Then do a
<i>heap_endscan().</i> <i>Keys</i> can be assigned to the <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 <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> compared to the keys, and only the valid rows returned.</P>
<p>You can also use <i>heap_fetch()</i> to fetch rows by block <P>You can also use <I>heap_fetch()</I> to fetch rows by block
number/offset. While scans automatically lock/unlock rows from the number/offset. While scans automatically lock/unlock rows from the
buffer cache, with <i>heap_fetch(),</i> you must pass a buffer cache, with <I>heap_fetch(),</I> you must pass a
<i>Buffer</i> pointer, and <i>ReleaseBuffer()</i> it when <I>Buffer</I> pointer, and <I>ReleaseBuffer()</I> it when
completed.</p> completed.</P>
<p>Once you have the row, you can get data that is common to all <P>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 tuples, like <I>t_self</I> and <I>t_oid,</I> by merely accessing
the <i>HeapTuple</i> structure entries. If you need a the <I>HeapTuple</I> structure entries. If you need a
table-specific column, you should take the HeapTuple pointer, and table-specific column, you should take the HeapTuple pointer, and
use the <i>GETSTRUCT()</i> macro to access the table-specific start 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> 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 pointer if you are accessing the pg_proc table, or
<i>Form_pg_type</i> if you are accessing pg_type. You can then <I>Form_pg_type</I> if you are accessing pg_type. You can then
access the columns by using a structure pointer:</p> access the columns by using a structure pointer:</P>
<PRE>
<pre> <CODE>((Form_pg_class) GETSTRUCT(tuple))-&gt;relnatts
<code>((Form_pg_class) GETSTRUCT(tuple))-&gt;relnatts </CODE>
</code> </PRE>
</pre> You must not directly change <I>live</I> tuples in this way. The
best way is to use <I>heap_modifytuple()</I> and pass it your
You must not directly change <i>live</i> tuples in this way. The original tuple, and the values you want changed. It returns a
best way is to use <i>heap_modifytuple()</i> and pass it your palloc'ed tuple, which you pass to <I>heap_replace().</I> You can
original tuple, and the values you want changed. It returns a delete tuples by passing the tuple's <I>t_self</I> to
palloc'ed tuple, which you pass to <i>heap_replace().</i> You can <I>heap_destroy().</I> You use <I>t_self</I> for
delete tuples by passing the tuple's <i>t_self</i> to <I>heap_update()</I> too. Remember, tuples can be either system
<i>heap_destroy().</i> You use <i>t_self</i> for cache copies, which may go away after you call
<i>heap_update()</i> too. Remember, tuples can be either system <I>ReleaseSysCache()</I>, or read directly from disk buffers, which
cache copies, which may go away after you call go away when you <I>heap_getnext()</I>, <I>heap_endscan</I>, or
<i>ReleaseSysCache()</i>, or read directly from disk buffers, which <I>ReleaseBuffer()</I>, in the <I>heap_fetch()</I> case. Or it may
go away when you <i>heap_getnext()</i>, <i>heap_endscan</i>, or be a palloc'ed tuple, that you must <I>pfree()</I> when finished.
<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="2.2">2.2</A>) Why are table, column, type, function,
<h3><a name="2.2">2.2</a>) Why are table, column, type, function, view names sometimes referenced as <I>Name</I> or <I>NameData,</I>
view names sometimes referenced as <i>Name</i> or <i>NameData,</i> and sometimes as <I>char *?</I></H3>
and sometimes as <i>char *?</i></h3>
<P>Table, column, type, function, and view names are stored in
<p>Table, column, type, function, and view names are stored in system tables in columns of type <I>Name.</I> Name is a
system tables in columns of type <i>Name.</i> Name is a fixed-length, null-terminated type of <I>NAMEDATALEN</I> bytes.
fixed-length, null-terminated type of <i>NAMEDATALEN</i> bytes. (The default value for NAMEDATALEN is 64 bytes.)</P>
(The default value for NAMEDATALEN is 64 bytes.)</p> <PRE>
<CODE>typedef struct nameData
<pre>
<code>typedef struct nameData
{ {
char data[NAMEDATALEN]; char data[NAMEDATALEN];
} NameData; } NameData;
typedef NameData *Name; typedef NameData *Name;
</code> </CODE>
</pre> </PRE>
Table, column, type, function, and view names that come into the
Table, column, type, function, and view names that come into the backend via user queries are stored as variable-length,
backend via user queries are stored as variable-length, null-terminated character strings.
null-terminated character strings.
<p>Many functions are called with both types of names, ie. <P>Many functions are called with both types of names, ie.
<i>heap_open().</i> Because the Name type is null-terminated, it is <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 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 many cases where on-disk names(Name) are compared to user-supplied
names(char *), there are many cases where Name and char * are used names(char *), there are many cases where Name and char * are used
interchangeably.</p> interchangeably.</P>
<h3><a name="2.3">2.3</a>) Why do we use <i>Node</i> and <H3><A name="2.3">2.3</A>) Why do we use <I>Node</I> and
<i>List</i> to make data structures?</h3> <I>List</I> to make data structures?</H3>
<p>We do this because this allows a consistent way to pass data <P>We do this because this allows a consistent way to pass data
inside the backend in a flexible way. Every node has a inside the backend in a flexible way. Every node has a
<i>NodeTag</i> which specifies what type of data is inside the <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 Node. <I>Lists</I> are groups of <I>Nodes chained together as a
forward-linked list.</i></p> forward-linked list.</I></P>
<p>Here are some of the <i>List</i> manipulation commands:</p> <P>Here are some of the <I>List</I> manipulation commands:</P>
<blockquote> <BLOCKQUOTE>
<dl> <DL>
<dt>lfirst(i), lfirst_int(i), lfirst_oid(i)</dt> <DT>lfirst(i), lfirst_int(i), lfirst_oid(i)</DT>
<dd>return the data (a point, inteter and OID respectively) at list <DD>return the data (a point, inteter and OID respectively) at
element <i>i.</i></dd> list element <I>i.</I></DD>
<dt>lnext(i)</dt> <DT>lnext(i)</DT>
<dd>return the next list element after <i>i.</i></dd> <DD>return the next list element after <I>i.</I></DD>
<dt>foreach(i, list)</dt> <DT>foreach(i, list)</DT>
<dd>loop through <i>list,</i> assigning each list element to <DD>
<i>i.</i> It is important to note that <i>i</i> is a List *, not loop through <I>list,</I> assigning each list element to
the data in the <i>List</i> element. You need to use <I>i.</I> It is important to note that <I>i</I> is a List *,
<i>lfirst(i)</i> to get at the data. Here is a typical code snippet not the data in the <I>List</I> element. You need to use
that loops through a List containing <i>Var *'s</i> and processes <I>lfirst(i)</I> to get at the data. Here is a typical code
each one: snippet that loops through a List containing <I>Var *'s</I>
<pre> and processes each one:
<code> List *list; <PRE>
<CODE> List *list;
ListCell *i; ListCell *i;
foreach(i, list) foreach(i, list)
...@@ -838,114 +833,112 @@ each one: ...@@ -838,114 +833,112 @@ each one:
/* process var here */ /* process var here */
} }
</code> </CODE>
</pre> </PRE>
</dd> </DD>
<dt>lcons(node, list)</dt>
<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></dd>
<dt>lappend(list, node)</dt> <DT>lcons(node, list)</DT>
<dd>add <i>node</i> to the end of <i>list.</i> This is more <DD>add <I>node</I> to the front of <I>list,</I> or create a
expensive that lcons.</dd> new list with <I>node</I> if <I>list</I> is <I>NIL.</I></DD>
<dt>nconc(list1, list2)</dt> <DT>lappend(list, node)</DT>
<dd>Concat <i>list2</i> on to the end of <i>list1.</i></dd> <DD>add <I>node</I> to the end of <I>list.</I> This is more
expensive that lcons.</DD>
<dt>length(list)</dt> <DT>nconc(list1, list2)</DT>
<dd>return the length of the <i>list.</i></dd> <DD>Concat <I>list2</I> on to the end of <I>list1.</I></DD>
<dt>nth(i, list)</dt> <DT>length(list)</DT>
<dd>return the <i>i</i>'th element in <i>list.</i></dd> <DD>return the length of the <I>list.</I></DD>
<dt>lconsi, ...</dt> <DT>nth(i, list)</DT>
<dd>There are integer versions of these: <i>lconsi, lappendi</i>, <DD>return the <I>i</I>'th element in <I>list.</I></DD>
etc. Also versions for OID lists: <i>lconso, lappendo</i>,
etc.</dd>
</dl>
</blockquote>
You can print nodes easily inside <i>gdb.</i> First, to disable <DT>lconsi, ...</DT>
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 <DD>There are integer versions of these: <I>lconsi,
commands to print out List, Node, and structure contents in a lappendi</I>, etc. Also versions for OID lists: <I>lconso,
verbose format that is easier to understand. List's are unrolled lappendo</I>, etc.</DD>
into nodes, and nodes are printed in detail. The first prints in a </DL>
short format, and the second in a long format: </BLOCKQUOTE>
<pre> You can print nodes easily inside <I>gdb.</I> First, to disable
<code>(gdb) call print(any_pointer) 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) (gdb) call pprint(any_pointer)
</code> </CODE>
</pre> </PRE>
The output appears in the postmaster log file, or on your screen if
The output appears in the postmaster log file, or on your screen if you are running a backend directly without a postmaster.
you are running a backend directly without a postmaster.
<h3><a name="2.4">2.4</a>) I just added a field to a structure. <H3><A name="2.4">2.4</A>) I just added a field to a structure.
What else should I do?</h3> What else should I do?</H3>
<p>The structures passing around from the parser, rewrite, <P>The structures passing around from the parser, rewrite,
optimizer, and executor require quite a bit of support. Most optimizer, and executor require quite a bit of support. Most
structures have support routines in <i>src/backend/nodes</i> used structures have support routines in <I>src/backend/nodes</I> used
to create, copy, read, and output those structures (in particular, to create, copy, read, and output those structures (in particular,
the files <i>copyfuncs.c</i> and <i>equalfuncs.c</i>. Make sure you the files <I>copyfuncs.c</I> and <I>equalfuncs.c</I>. Make sure you
add support for your new field to these files. Find any other 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> places the structure may need code for your new field. <I>mkid</I>
is helpful with this (see <a href="#1.9">1.9</a>).</p> is helpful with this (see <A href="#1.9">1.9</A>).</P>
<h3><a name="2.5">2.5</a>) Why do we use <i>palloc</i>() and <H3><A name="2.5">2.5</A>) Why do we use <I>palloc</I>() and
<i>pfree</i>() to allocate memory?</h3> <I>pfree</I>() to allocate memory?</H3>
<p><i>palloc()</i> and <i>pfree()</i> are used in place of malloc() <P><I>palloc()</I> and <I>pfree()</I> are used in place of malloc()
and free() because we find it easier to automatically free all and free() because we find it easier to automatically free all
memory allocated when a query completes. This assures us that all memory allocated when a query completes. This assures us that all
memory that was allocated gets freed even if we have lost track of memory that was allocated gets freed even if we have lost track of
where we allocated it. There are special non-query contexts that where we allocated it. There are special non-query contexts that
memory can be allocated in. These affect when the allocated memory memory can be allocated in. These affect when the allocated memory
is freed by the backend.</p> is freed by the backend.</P>
<h3><a name="2.6">2.6</a>) What is ereport()?</h3> <H3><A name="2.6">2.6</A>) What is ereport()?</H3>
<p><i>ereport()</i> is used to send messages to the front-end, and <P><I>ereport()</I> is used to send messages to the front-end, and
optionally terminate the current query being processed. The first optionally terminate the current query being processed. The first
parameter is an ereport level of <i>DEBUG</i> (levels 1-5), parameter is an ereport level of <I>DEBUG</I> (levels 1-5),
<i>LOG,</i> <i>INFO,</i> <i>NOTICE,</i> <i>ERROR,</i> <i>FATAL,</i> <I>LOG,</I> <I>INFO,</I> <I>NOTICE,</I> <I>ERROR,</I> <I>FATAL,</I>
or <i>PANIC.</i> <i>NOTICE</i> prints on the user's terminal and or <I>PANIC.</I> <I>NOTICE</I> prints on the user's terminal and
the postmaster logs. <i>INFO</i> prints only to the user's terminal the postmaster logs. <I>INFO</I> prints only to the user's terminal
and <i>LOG</i> prints only to the server logs. (These can be and <I>LOG</I> prints only to the server logs. (These can be
changed from <i>postgresql.conf.</i>) <i>ERROR</i> prints in both changed from <I>postgresql.conf.</I>) <I>ERROR</I> prints in both
places, and terminates the current query, never returning from the places, and terminates the current query, never returning from the
call. <i>FATAL</i> terminates the backend process. The remaining call. <I>FATAL</I> terminates the backend process. The remaining
parameters of <i>ereport</i> are a <i>printf</i>-style set of parameters of <I>ereport</I> are a <I>printf</I>-style set of
parameters to print.</p> parameters to print.</P>
<p><i>ereport(ERROR)</i> frees most memory and open file <P><I>ereport(ERROR)</I> frees most memory and open file
descriptors so you don't need to clean these up before the descriptors so you don't need to clean these up before the
call.</p> call.</P>
<h3><a name="2.7">2.7</a>) What is CommandCounterIncrement()?</h3> <H3><A name="2.7">2.7</A>) What is CommandCounterIncrement()?</H3>
<p>Normally, transactions can not see the rows they modify. This <P>Normally, transactions can not see the rows they modify. This
allows <code>UPDATE foo SET x = x + 1</code> to work correctly.</p> allows <CODE>UPDATE foo SET x = x + 1</CODE> to work correctly.</P>
<p>However, there are cases where a transactions needs to see rows <P>However, there are cases where a transactions needs to see rows
affected in previous parts of the transaction. This is accomplished affected in previous parts of the transaction. This is accomplished
using a Command Counter. Incrementing the counter allows using a Command Counter. Incrementing the counter allows
transactions to be broken into pieces so each piece can see rows transactions to be broken into pieces so each piece can see rows
modified by previous pieces. <i>CommandCounterIncrement()</i> modified by previous pieces. <I>CommandCounterIncrement()</I>
increments the Command Counter, creating a new part of the increments the Command Counter, creating a new part of the
transaction.</p> transaction.</P>
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