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| author | Magnus Hagander | 2008-04-22 09:26:36 +0000 |
|---|---|---|
| committer | Magnus Hagander | 2008-04-22 09:26:36 +0000 |
| commit | a357880dde5e932edc9f8dabaeb341ffa4ff61a0 (patch) | |
| tree | fe3621cd5e68ca709cc8737d00570ed2a11cca3e /doc/src | |
| parent | e5fc7184cedd501faf50d044c8b95b915d3f9d49 (diff) | |
Replace developer FAQ with a reference to the wiki, which is where
it now lives (per discussion). Leave the other FAQs alone for now.
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/FAQ/FAQ_DEV.html | 992 |
1 files changed, 2 insertions, 990 deletions
diff --git a/doc/src/FAQ/FAQ_DEV.html b/doc/src/FAQ/FAQ_DEV.html index 7acb76feb94..09d02f6a73c 100644 --- a/doc/src/FAQ/FAQ_DEV.html +++ b/doc/src/FAQ/FAQ_DEV.html @@ -2,1001 +2,13 @@ <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: Thu Oct 27 09:48:14 EDT 2005</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/files/documentation/faqs/FAQ_DEV.html">http://www.postgresql.org/files/documentation/faqs/FAQ_DEV.html</A>.</P> - <HR> - <BR> - - - <H2>General Questions</H2> - <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>) I've developed a patch, what next?<BR> - <A href="#1.6">1.6</A>) Where can I learn more about the code?<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, <insert your favorite wizz-bang feature - here>?<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> - - - <H2>Technical Questions</H2> - <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> - <A href="#2.8">2.8</A>) What debugging features are available?<BR> - - <BR> - - <HR> - - <H2>General Questions</H2> - - <H3><A name="1.1">1.1</A>) How do 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.postgresql.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://www.postgresql.org/docs/faqs.TODO.html"> - http://www.postgresql.org/docs/faqs.TODO.html</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 because others might be working on the same - TODO item, or you might have misunderstood the TODO item. In the - email, discuss both the internal implementation method you plan to - use, and any user-visible changes (new syntax, etc). For complex - patches, it is important to get community feeback on your proposal - before starting work. Failure to do so might mean your patch is - rejected.</P> - - <P>A web site is maintained for patches awaiting review, - <a href="http://momjian.postgresql.org/cgi-bin/pgpatches"> - http://momjian.postgresql.org/cgi-bin/pgpatches</a>, and - those that are being kept for the next release, - <a href="http://momjian.postgresql.org/cgi-bin/pgpatches_hold"> - http://momjian.postgresql.org/cgi-bin/pgpatches2</a>.</P> - - <H3><A name="1.5">1.5</A>) I've developed a patch, what next?</H3> - - <P>Generate the patch in contextual diff format. If you are - unfamiliar with this, you might 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 will be - either accepted or sent back for further work. Also, please try to - include documentation changes as part of the patch. If you can't do - that, let us know and we will manually update the documentation when - the patch is applied.</P> - - <H3><A name="1.6">1.6</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://www.postgresql.org/developer"> - http://www.postgresql.org/developer</A>.</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 might want to take advantage of anonymous - access to our source code management system. The source tree is - 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> - - <H3><A name="1.8">1.8</A>) How do I test my changes?</H3> - - <P><B>Basic system testing</B></P> - - <P>The easiest way to test your code is to ensure that it builds - against the latest version of the code and that it does not generate - compiler warnings.</P> - - <P>It is worth advised that you pass --enable-cassert to - <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>Regression test suite</B></P> - - <P>The next step is to test your changes against the existing - regression test suite. To do this, issue "make check" in the root - directory of the source tree. If any tests failure, - investigate.</P> - - <P>If you've deliberately changed existing behavior, this change - might 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>Some developers make use of tools such as valgrind (<A href= - "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><B>What about unit testing, static analysis, model - checking...?</B></P> - - <P>There have been a number of discussions about other testing - frameworks and some developers are exploring these ideas.</P> - - <P>Keep in mind the <I>Makefiles</I> do not have the proper - dependencies for include files. You have to do a <I>make clean</I> - and then another <I>make</I>. If you are using <SMALL>GCC</SMALL> - you can use the <I>--enable-depend</I> option of <I>configure</I> - to have the compiler compute the dependencies automatically.</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 - backend description/flowchart of the backend directories - ccsym find standard defines made by your compiler - copyright fixes copyright notices - - entab converts tabs to spaces, used by pgindent - find_static finds functions that could be made static - find_typedef finds typedefs in the source code - find_badmacros finds macros that use braces incorrectly - fsync a script to provide information about the cost of cache - syncing system calls - 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 make comparison of our keywords and SQL'92 - make_mkid make mkid ID files - pgcvslog used to generate a list of changes for each release - pginclude scripts for adding/removing include files - pgindent indents source files - pgtest a semi-automated build system - thread a thread testing script -</PRE> - - <P>In <I>src/include/catalog</I>:</P> -<PRE> - unused_oids a script which generates unused OIDs for use in system - catalogs - duplicate_oids finds duplicate OIDs in system catalog definitions -</PRE> - If you point your browser at the <I>tools/backend/index.html</I> - file, 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> - - <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> - - <P>By running <I>tools/make_mkid</I>, an archive of source symbols - can be created that can be rapidly queried.</P> - - <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 - glimpse, which can be found at <A href= - "http://webglimpse.net/">http://webglimpse.net/</A>.</P> - - <P><I>tools/make_diff</I> has tools to create patch diff files that - can be applied to the distribution. This produces context diffs, - which is our preferred format.</P> - - <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> - </P> -<PRE> - vi in ~/.exrc: - set tabstop=4 - set sw=4 - more: - more -x4 - less: - less -x4 - emacs: - M-x set-variable tab-width - - or - - (c-add-style "pgsql" - '("bsd" - (indent-tabs-mode . t) - (c-basic-offset . 4) - (tab-width . 4) - (c-offsets-alist . - ((case-label . +))) - ) - nil ) ; t = set this style, nil = don't - - (defun pgsql-c-mode () - (c-mode) - (c-set-style "pgsql") - ) - - and add this to your autoload list (modify file path in macro): - - (setq auto-mode-alist - (cons '("\\`/home/andrew/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> This <A href= - "http://ezine.daemonnews.org/200112/single_coding_style.html">article</A> - describes the value of a consistent coding style. - - <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.</P> - - <P><I>pginclude</I> contains scripts used to add needed - <CODE>#include</CODE>'s to include files, and removed unneeded - <CODE>#include</CODE>'s.</P> - - <P>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.</P> - - <H3><A name="1.10">1.10</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> - - <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>.</P> - - <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 - 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> - - <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> - - <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="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 - 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> - - <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> - - <H3><A name="1.13">1.13</A>) Why don't you use threads, raw - devices, async-I/O, <insert your favorite wizz-bang feature - here>?</H3> - - <P>There is always a temptation to use the newest operating system - features as soon as they arrive. We resist that temptation.</P> - - <P>First, we support 15+ operating systems, so any new feature has - to be well established before we will consider it. Second, most new - <I>wizz-bang</I> features don't provide <I>dramatic</I> - improvements. Third, they usually have some downside, such as - decreased reliability or additional code required. Therefore, we - 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 - improvement is possible.</P> - - <P>As an example, threads are not currently used in the backend - code because:</P> - - <UL> - <LI>Historically, threads were unsupported and buggy.</LI> - - <LI>An error in one backend can corrupt other backends.</LI> - - <LI>Speed improvements using threads are small compared to the - remaining backend startup time.</LI> - - <LI>The backend code would be more complex.</LI> - </UL> - - <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 - to discussions showing our reasoning in these areas.</P> - - <H3><A name="1.14">1.14</A>) How are RPMs packaged?</H3> - - <P>This was written by Lamar Owen:</P> - - <P>2001-05-03</P> - - <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 - paradigm. 'How is the RPM built?' is a multifaceted question. The - obvious simple answer is that I maintain:</P> - - <OL> - <LI>A set of patches to make certain portions of the source tree - 'behave' in the different environment of the RPMset;</LI> - - <LI>The initscript;</LI> - - <LI>Any other ancillary scripts and files;</LI> - - <LI>A README.rpm-dist document that tries to adequately document - both the differences between the RPM build and the WHY of the - differences, as well as useful RPM environment operations (like, - using syslog, upgrading, getting postmaster to start at OS boot, - etc);</LI> + <P>The developer FAQ can be found on the PostgreSQL wiki:</P> - <LI>The spec file that throws it all together. This is not a - trivial undertaking in a package of this size.</LI> - </OL> - - <P>I then download and build on as many different canonical - 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 - opportunity from certain commercial enterprises such as Great - Bridge and PostgreSQL, Inc. to build on other distributions.</P> - - <P>I test the build by installing the resulting packages and - running the regression tests. Once the build passes these tests, I - upload to the postgresql.org ftp server and make a release - announcement. I am also responsible for maintaining the RPM - download area on the ftp site.</P> - - <P>You'll notice I said 'canonical' distributions above. That - simply means that the machine is as stock 'out of the box' as - practical -- that is, everything (except select few programs) on - these boxen are installed by RPM; only official Red Hat released - RPMs are used (except in unusual circumstances involving software - that will not alter the build -- for example, installing a newer - 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 - 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 - the standard released 'official to that release' compiler is used - -- and only the standard official kernel is used as well.</P> - - <P>For a time I built on Mandrake for RedHat consumption -- no - more. Nonstandard RPM building systems are worse than useless. - Which is not to say that Mandrake is useless! By no means is - 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 - 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! - :-)</P> - - <P>I _do_ attempt to make the _source_ RPM compatible with as many - distributions as possible -- however, since I have limited - resources (as a volunteer RPM maintainer) I am limited as to the - amount of testing said build will get on other distributions, - architectures, or systems.</P> - - <P>And, while I understand people's desire to immediately upgrade - to the newest version, realize that I do this as a side interest -- - I have a regular, full-time job as a broadcast - engineer/webmaster/sysadmin/Technical Director which occasionally - 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 - much on the ball for the Release Candidates and the final - release.</P> - - <P>I am working towards a more open RPM distribution -- I would - dearly love to more fully document the process and put everything - 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 - 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 - a real spec file from a CVS spec-source file that would add version - numbers, changelog entries, etc to the result before building 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 - 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, - 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. - 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 - 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 - 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 - opposed to the idea -- not to keep the stuff to myself, but to not - hinder the platform-neutral stance. IMHO, of course.</P> - - <P>Of course, there are many projects that DO include all the files - necessary to build RPMs from their Official Tarball (TM).</P> - - <H3><A name="1.15">1.15</A>) How are CVS branches managed?</H3> - - <P>This was written by Tom Lane:</P> - - <P>2001-05-07</P> - - <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 - 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 - the "branch" portions of our CVS repository. We normally fork off a - branch for a stable release just before starting the development - cycle for the next release.</P> - - <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 - 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 - for pointing out that this is the easiest way to do it.) Typical - branch names are:</P> -<PRE> - REL7_1_STABLE - REL7_0_PATCHES - REL6_5_PATCHES -</PRE> - - <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 - 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 - your work. (And you *better* test your work. Never forget that - 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 - doubly sure that it's correct.)</P> - - <P>Normally, to checkout the head branch, you just cd to the place - you want to contain the toplevel "pgsql" directory and say</P> -<PRE> - cvs ... checkout pgsql -</PRE> - - <P>To get a past branch, you cd to wherever you want it and - say</P> -<PRE> - cvs ... checkout -r BRANCHNAME pgsql -</PRE> - - <P>For example, just a couple days ago I did</P> -<PRE> - mkdir ~postgres/REL7_1 - cd ~postgres/REL7_1 - cvs ... checkout -r REL7_1_STABLE pgsql -</PRE> - - <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 - "sticky": CVS automatically knows that this directory tree is for - 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, - 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 - 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 - 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 - dot-release or two, so that we won't have to double-patch the first - wave of fixes.</P> - - <H3><A name="1.16">1.16</A>) Where can I get a copy of the SQL - standards?</H3> - - <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 - be downloaded from:</P> - - <UL> - <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> - - <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</A></LI> - - <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> - </UL> - - <P>Some SQL standards web pages are:</P> - - <UL> - <LI><A href= - "http://troels.arvin.dk/db/rdbms/links/#standards">http://troels.arvin.dk/db/rdbms/links/#standards</A></LI> - - <LI><A href= - "http://www.wiscorp.com/SQLStandards.html">http://www.wiscorp.com/SQLStandards.html</A></LI> - - <LI><A href= - "http://www.contrib.andrew.cmu.edu/~shadow/sql.html#syntax">http://www.contrib.andrew.cmu.edu/~shadow/sql.html#syntax</A> - (SQL-92)</LI> - - <LI><A href= - "http://dbs.uni-leipzig.de/en/lokal/standards.pdf">http://dbs.uni-leipzig.de/en/lokal/standards.pdf</A> - (paper)</LI> - </UL> - - <H3><A name="1.17">1.17</A>) Where can I get technical - assistance?</H3> - - <P>Many technical questions held by those new to the code have been - answered on the pgsql-hackers mailing list - the archives of which - can be found at <A href= - "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 - free to put it to the list.</P> - - <P>Major contributors also answer technical questions, including - questions about development of new features, on IRC at - irc.freenode.net in the #postgresql channel.</P> - - <H3><A name="1.18">1.18</A>) How do I get involved in PostgreSQL - web site development?</H3> - - <P>PostgreSQL website development is discussed on the - pgsql-www@postgresql.org mailing list. The is a project page where - 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> - , the code for the next version of the website is under the - "portal" module. You will also find code for the "techdocs" - website if you would like to contribute to that. A temporary todo - list for current website development issues is available at <A - href= - "http://xzilla.postgresql.org/todo">http://xzilla.postgresql.org/todo</A></P> - - <H2>Technical Questions</H2> - - <H3><A name="2.1">2.1</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>SearchSysCache()</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> - - <P>The rows returned are cache-owned versions of the heap rows. - Therefore, you must not modify or delete the tuple returned by - <I>SearchSysCache()</I>. What you <I>should</I> do is release it - with <I>ReleaseSysCache()</I> when you are done using it; this - informs the cache that it can discard that tuple if necessary. If - you neglect to call <I>ReleaseSysCache()</I>, then the cache entry - will remain locked in the cache until end of transaction, which is - tolerable but not very desirable.</P> - - <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> - - <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> - - <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.</P> - - <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 - 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:</P> -<PRE> -<CODE>((Form_pg_class) GETSTRUCT(tuple))->relnatts -</CODE> -</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 - original tuple, and the values you want changed. It returns a - 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 use <I>t_self</I> for - <I>heap_update()</I> too. Remember, tuples can be either system - cache copies, which might go away after you call - <I>ReleaseSysCache()</I>, or read directly from disk buffers, 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="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></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 64 bytes.)</P> -<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="2.3">2.3</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> - - <P>Here are some of the <I>List</I> manipulation commands:</P> - - <BLOCKQUOTE> - <DL> - <DT>lfirst(i), lfirst_int(i), lfirst_oid(i)</DT> - - <DD>return the data (a point, integer and OID respectively) at - list element <I>i.</I></DD> - - <DT>lnext(i)</DT> - - <DD>return the next list element after <I>i.</I></DD> - - <DT>foreach(i, list)</DT> - - <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 - snippet that loops through a List containing <I>Var *'s</I> - and processes each one: -<PRE> -<CODE> List *list; - ListCell *i; - - foreach(i, list) - { - Var *var = lfirst(i); - - /* process var here */ - } -</CODE> -</PRE> - </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> - - <DD>add <I>node</I> to the end of <I>list.</I> This is more - expensive that lcons.</DD> - - <DT>nconc(list1, list2)</DT> - - <DD>Concat <I>list2</I> on to the end of <I>list1.</I></DD> - - <DT>length(list)</DT> - - <DD>return the length of the <I>list.</I></DD> - - <DT>nth(i, list)</DT> - - <DD>return the <I>i</I>'th element in <I>list.</I></DD> - - <DT>lconsi, ...</DT> - - <DD>There are integer versions of these: <I>lconsi, - lappendi</I>, 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 - 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. - - <H3><A name="2.4">2.4</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 (in particular, - 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 - places the structure might need code for your new field. <I>mkid</I> - 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 - <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 find it easier to automatically free 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 - where we allocated it. There are special non-query contexts that - memory can be allocated in. These affect when the allocated memory - is freed by the backend.</P> - - <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 - optionally terminate the current query being processed. The first - 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> - 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 - 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 - places, and terminates the current query, never returning from the - call. <I>FATAL</I> terminates the backend process. The remaining - parameters of <I>ereport</I> are a <I>printf</I>-style set of - parameters to print.</P> - - <P><I>ereport(ERROR)</I> frees most memory and open file - descriptors so you don't need to clean these up before the - call.</P> - - <H3><A name="2.7">2.7</A>) What is CommandCounterIncrement()?</H3> - - <P>Normally, transactions can not see the rows they modify. This - 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 - affected in previous parts of the transaction. This is accomplished - using a Command Counter. Incrementing the counter allows - transactions to be broken into pieces so each piece can see rows - modified by previous pieces. <I>CommandCounterIncrement()</I> - increments the Command Counter, creating a new part of the - transaction.</P> - - <H3><A name="2.8">2.8</A>) What debugging features are - available?</H3> - - <P>First, try running <I>configure</I> with the --enable-cassert - option, many <I>assert()</I>s monitor the progress of the backend - and halt the program when something unexpected occurs.</P> - - <P>The <I>postmaster</I> has a <I>-d</I> option that allows even more - detailed information to be reported. The <I>-d</I> option takes a - number that specifies the debug level. Be warned that high debug - level values generate large log files.</P> - - <P>If the <I>postmaster</I> is not running, you can actually run the - <I>postgres</I> backend from the command line, and type your - <SMALL>SQL</SMALL> statement directly. This is recommended - <B>only</B> for debugging purposes. If you have compiled with debugging - symbols, you can use a debugger to see what is happening. Because - the backend was not started from <I>postmaster</I>, it is not - running in an identical environment and locking/backend interaction - problems might not be duplicated.</P> - - <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> using <CODE>SELECT pg_backend_pid()</CODE>. - Use a debugger to attach to the <I>postgres</I> <SMALL>PID</SMALL>. - You can set breakpoints in the debugger and issue queries from the - other. If you are looking to find the location that is generating - an error or log message, set a breakpoint at <I>errfinish</>. - - <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 to the process with - the debugger, set any breakpoints, and continue through the startup - sequence.</P> - - <P>You can also compile with profiling to see what functions are - taking execution time. The backend profile files will be deposited - in the <I>pgsql/data</I> directory. The client profile file will be - put in the client's current directory. Linux requires a compile with - <I>-DLINUX_PROFILE</I> for proper profiling.</P> +<P><A href="http://wiki.postgresql.org/wiki/Development_information">http://wiki.postgresql.org/wiki/Development_information</A></P> </BODY> </HTML> - |