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Green_GoodERP18_FSJ_Standard/PostgreSQL/doc/postgresql/html/plperl-under-the-hood.html

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  1. <?xml version="1.0" encoding="UTF-8" standalone="no"?>

  2. <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>44.8. PL/Perl Under the Hood</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="prev" href="plperl-event-triggers.html" title="44.7. PL/Perl Event Triggers" /><link rel="next" href="plpython.html" title="Chapter 45. PL/Python - Python Procedural Language" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">44.8. PL/Perl Under the Hood</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="plperl-event-triggers.html" title="44.7. PL/Perl Event Triggers">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="plperl.html" title="Chapter 44. PL/Perl - Perl Procedural Language">Up</a></td><th width="60%" align="center">Chapter 44. PL/Perl - Perl Procedural Language</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="plpython.html" title="Chapter 45. PL/Python - Python Procedural Language">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="PLPERL-UNDER-THE-HOOD"><div class="titlepage"><div><div><h2 class="title" style="clear: both">44.8. PL/Perl Under the Hood</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="plperl-under-the-hood.html#PLPERL-CONFIG">44.8.1. Configuration</a></span></dt><dt><span class="sect2"><a href="plperl-under-the-hood.html#PLPERL-MISSING">44.8.2. Limitations and Missing Features</a></span></dt></dl></div><div class="sect2" id="PLPERL-CONFIG"><div class="titlepage"><div><div><h3 class="title">44.8.1. Configuration</h3></div></div></div><p>

  3.   This section lists configuration parameters that affect <span class="application">PL/Perl</span>.

  4.   </p><div class="variablelist"><dl class="variablelist"><dt id="GUC-PLPERL-ON-INIT"><span class="term">

  5.        <code class="varname">plperl.on_init</code> (<code class="type">string</code>)

  6.       <a id="id-1.8.10.16.2.3.1.1.3" class="indexterm"></a>

  7.       </span></dt><dd><p>

  8.         Specifies Perl code to be executed when a Perl interpreter is first

  9.         initialized, before it is specialized for use by <code class="literal">plperl</code> or

  10.         <code class="literal">plperlu</code>.

  11.         The SPI functions are not available when this code is executed.

  12.         If the code fails with an error it will abort the initialization of

  13.         the interpreter and propagate out to the calling query, causing the

  14.         current transaction or subtransaction to be aborted.

  15.        </p><p>

  16.        The Perl code is limited to a single string. Longer code can be placed

  17.        into a module and loaded by the <code class="literal">on_init</code> string.

  18.        Examples:

  19. </p><pre class="programlisting">

  20. plperl.on_init = 'require "plperlinit.pl"'

  21. plperl.on_init = 'use lib "/my/app"; use MyApp::PgInit;'

  22. </pre><p>

  23.        </p><p>

  24.        Any modules loaded by <code class="literal">plperl.on_init</code>, either directly or

  25.        indirectly, will be available for use by <code class="literal">plperl</code>.  This may

  26.        create a security risk. To see what modules have been loaded you can use:

  27. </p><pre class="programlisting">

  28. DO 'elog(WARNING, join ", ", sort keys %INC)' LANGUAGE plperl;

  29. </pre><p>

  30.        </p><p>

  31.         Initialization will happen in the postmaster if the <code class="literal">plperl</code> library is

  32.         included in <a class="xref" href="runtime-config-client.html#GUC-SHARED-PRELOAD-LIBRARIES">shared_preload_libraries</a>, in which

  33.         case extra consideration should be given to the risk of destabilizing

  34.         the postmaster.  The principal reason for making use of this feature

  35.         is that Perl modules loaded by <code class="literal">plperl.on_init</code> need be

  36.         loaded only at postmaster start, and will be instantly available

  37.         without loading overhead in individual database sessions.  However,

  38.         keep in mind that the overhead is avoided only for the first Perl

  39.         interpreter used by a database session — either PL/PerlU, or

  40.         PL/Perl for the first SQL role that calls a PL/Perl function.  Any

  41.         additional Perl interpreters created in a database session will have

  42.         to execute <code class="literal">plperl.on_init</code> afresh.  Also, on Windows there

  43.         will be no savings whatsoever from preloading, since the Perl

  44.         interpreter created in the postmaster process does not propagate to

  45.         child processes.

  46.        </p><p>

  47.        This parameter can only be set in the <code class="filename">postgresql.conf</code> file or on the server command line.

  48.        </p></dd><dt id="GUC-PLPERL-ON-PLPERL-INIT"><span class="term">

  49.        <code class="varname">plperl.on_plperl_init</code> (<code class="type">string</code>)

  50.        <a id="id-1.8.10.16.2.3.2.1.3" class="indexterm"></a>

  51.       <br /></span><span class="term">

  52.        <code class="varname">plperl.on_plperlu_init</code> (<code class="type">string</code>)

  53.        <a id="id-1.8.10.16.2.3.2.2.3" class="indexterm"></a>

  54.       </span></dt><dd><p>

  55.         These parameters specify Perl code to be executed when a Perl

  56.         interpreter is specialized for <code class="literal">plperl</code> or

  57.         <code class="literal">plperlu</code> respectively.  This will happen when a PL/Perl or

  58.         PL/PerlU function is first executed in a database session, or when

  59.         an additional interpreter has to be created because the other language

  60.         is called or a PL/Perl function is called by a new SQL role.  This

  61.         follows any initialization done by <code class="literal">plperl.on_init</code>.

  62.         The SPI functions are not available when this code is executed.

  63.         The Perl code in <code class="literal">plperl.on_plperl_init</code> is executed after

  64.         <span class="quote">“<span class="quote">locking down</span>”</span> the interpreter, and thus it can only perform

  65.         trusted operations.

  66.        </p><p>

  67.         If the code fails with an error it will abort the initialization and

  68.         propagate out to the calling query, causing the current transaction or

  69.         subtransaction to be aborted.  Any actions already done within Perl

  70.         won't be undone; however, that interpreter won't be used again.

  71.         If the language is used again the initialization will be attempted

  72.         again within a fresh Perl interpreter.

  73.        </p><p>

  74.         Only superusers can change these settings.  Although these settings

  75.         can be changed within a session, such changes will not affect Perl

  76.         interpreters that have already been used to execute functions.

  77.        </p></dd><dt id="GUC-PLPERL-USE-STRICT"><span class="term">

  78.        <code class="varname">plperl.use_strict</code> (<code class="type">boolean</code>)

  79.        <a id="id-1.8.10.16.2.3.3.1.3" class="indexterm"></a>

  80.       </span></dt><dd><p>

  81.         When set true subsequent compilations of PL/Perl functions will have

  82.         the <code class="literal">strict</code> pragma enabled.  This parameter does not affect

  83.         functions already compiled in the current session.

  84.        </p></dd></dl></div></div><div class="sect2" id="PLPERL-MISSING"><div class="titlepage"><div><div><h3 class="title">44.8.2. Limitations and Missing Features</h3></div></div></div><p>

  85.    The following features are currently missing from PL/Perl, but they

  86.    would make welcome contributions.

  87. 

  88.    </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>

  89.       PL/Perl functions cannot call each other directly.

  90.      </p></li><li class="listitem"><p>

  91.       SPI is not yet fully implemented.

  92.      </p></li><li class="listitem"><p>

  93.       If you are fetching very large data sets using

  94.       <code class="literal">spi_exec_query</code>, you should be aware that

  95.       these will all go into memory.  You can avoid this by using

  96.       <code class="literal">spi_query</code>/<code class="literal">spi_fetchrow</code> as

  97.       illustrated earlier.

  98.      </p><p>

  99.         A similar problem occurs if a set-returning function passes a

  100.         large set of rows back to PostgreSQL via <code class="literal">return</code>. You

  101.         can avoid this problem too by instead using

  102.         <code class="literal">return_next</code> for each row returned, as shown

  103.         previously.

  104.      </p></li><li class="listitem"><p>

  105.         When a session ends normally, not due to a fatal error, any

  106.         <code class="literal">END</code> blocks that have been defined are executed.

  107.         Currently no other actions are performed. Specifically,

  108.         file handles are not automatically flushed and objects are

  109.         not automatically destroyed.

  110.       </p></li></ul></div><p>

  111.   </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="plperl-event-triggers.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="plperl.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="plpython.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">44.7. PL/Perl Event Triggers </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 45. PL/Python - Python Procedural Language</td></tr></table></div></body></html>
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