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Commit1f7aa64

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Reorganize FAQ entry on performance.
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‎doc/FAQ

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Frequently Asked Questions (FAQ) for PostgreSQL
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Last updated:Sun Jan30 21:44:35 EST 2005
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Last updated:Mon Jan31 15:40:24 EST 2005
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Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
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By default, PostgreSQL only allows connections from the local machine
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using Unix domain sockets or TCP/IP connections. Other machines will
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not be able to connect unless you modify listen_addresses in the
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postgresql.confand enable host-based authentication by modifying the
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file $PGDATA/pg_hba.confaccordingly.
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postgresql.conffile, enable host-based authentication by modifying
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the $PGDATA/pg_hba.conffile, and restart the server.
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3.3) How do I tune the database engine for better performance?
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Certainly, indexes can speed up queries. The EXPLAIN ANALYZE command
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allows you to see how PostgreSQL is interpreting your query, and which
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indexes are being used.
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If you are doing many INSERTs, consider doing them in a large batch
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using the COPY command. This is much faster than individual INSERTS.
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Second, statements not in a BEGIN WORK/COMMIT transaction block are
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considered to be in their own transaction. Consider performing several
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statements in a single transaction block. This reduces the transaction
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overhead. Also, consider dropping and recreating indexes when making
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large data changes.
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There are several tuning options in the Administration Guide/Server
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Run-time Environment/Run-time Configuration. You can disable fsync()
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by using fsync option. This will prevent fsync()s from flushing to
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disk after every transaction.
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You can use the shared_buffers option to increase the number of shared
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memory buffers used by the backend processes. If you make this
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parameter too high, the postmaster may not start because you have
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exceeded your kernel's limit on shared memory space. Each buffer is 8K
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and the default is 1000 buffers.
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You can also use the sort_mem (from PostgreSQL 8.0: work_mem) options
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to increase the maximum amount of memory used by the backend processes
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for each temporary sort. The default is 1024 (i.e. 1MB).
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You can also use the CLUSTER command to group data in tables to match
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an index. See the CLUSTER manual page for more details.
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There are three major areas for potential performance improvement:
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Query Changes
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This involves modifying queries to obtain better performance:
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+ Creation of indexes, including expression and partial indexes
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+ Use of COPY instead of multiple INSERTs
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+ Grouping of multiple statements into a single transaction to
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reduce commit overhead
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+ Use of CLUSTER when retrieving many rows from an index
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+ Use of LIMIT for returning a subset of a query's output
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+ Use of Prepared queries
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+ Use of ANALYZE to maintain accurate optimizer statistics
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+ Regular use of VACUUM or pg_autovacuum
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+ Dropping of indexes during large data changes
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Server Configuration
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A number of postgresql.conf settings affect performance. For
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more details, see Administration Guide/Server Run-time
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Environment/Run-time Configuration for a full listing, and for
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commentary see
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http://www.varlena.com/varlena/GeneralBits/Tidbits/annotated_co
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nf_e.html and
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http://www.varlena.com/varlena/GeneralBits/Tidbits/perf.html.
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Hardware Selection
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The effect of hardware on performance is detailed in
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http://candle.pha.pa.us/main/writings/pgsql/hw_performance/inde
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x.html.
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3.4) What debugging features are available?
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PostgreSQL has several features that report status information that

‎doc/src/FAQ/FAQ.html

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alink="#0000ff">
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<H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1>
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<P>Last updated:Sun Jan30 21:44:35 EST 2005</P>
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<P>Last updated:Mon Jan31 15:40:24 EST 2005</P>
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<P>Current maintainer: Bruce Momjian (<Ahref=
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"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)
@@ -428,8 +428,8 @@ <H4><A name="2.3">2.3</A>) Does PostgreSQL have a graphical user
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RHDB Admin (<a
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href="http://sources.redhat.com/rhdb/">http://sources.redhat.com/rhd
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b/</a>), TORA (<a
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href="http://www.globecom.net/tora/">http://www.globecom.net/tora/</
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a>,partly commercial), and Rekall (<a
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href="http://www.globecom.net/tora/">http://www.globecom.net/tora/</a>,
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partly commercial), and Rekall (<a
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href="http://www.rekallrevealed.org/">
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http://www.rekallrevealed.org/</a>). There is also PhpPgAdmin (<a
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href="http://phppgadmin.sourceforge.net/">
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<P>By default, PostgreSQL only allows connections from the local
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machine using Unix domain sockets or TCP/IP connections. Other
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machines will not be able to connect unless you modify
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listen_addresses in the postgresql.conf<B>and</B> enable
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host-based authentication by modifying the file
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<I>$PGDATA/pg_hba.conf</I>accordingly.</P>
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<I>listen_addresses</I> in the<I>postgresql.conf</I> file, enable
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host-based authentication by modifying the
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<I>$PGDATA/pg_hba.conf</I>file, and restart the server.</P>
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<H4><Aname="3.3">3.3</A>) How do I tune the database engine for
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better performance?</H4>
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<P>Certainly, indexes can speed up queries. The
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<SMALL>EXPLAIN ANALYZE</SMALL> command allows you to see how
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PostgreSQL is interpreting your query, and which indexes are
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being used.</P>
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<P>If you are doing many<SMALL>INSERTs</SMALL>, consider doing
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them in a large batch using the<SMALL>COPY</SMALL> command. This
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is much faster than individual<SMALL>INSERTS</SMALL>. Second,
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statements not in a<SMALL>BEGIN WORK/COMMIT</SMALL> transaction
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block are considered to be in their own transaction. Consider
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performing several statements in a single transaction block. This
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reduces the transaction overhead. Also, consider dropping and
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recreating indexes when making large data changes.</P>
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<P>There are several tuning options in the<ahref=
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<P>There are three major areas for potential performance
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improvement:</P>
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<DL>
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<DT><B>Query Changes</B></DT>
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<DD>This involves modifying queries to obtain better
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performance:
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<ul>
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<li>Creation of indexes, including expression and partial
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indexes</li>
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<li>Use of COPY instead of multiple<SMALL>INSERT</SMALL>s</li>
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<li>Grouping of multiple statements into a single transaction to
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reduce commit overhead</li>
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<li>Use of<SMALL>CLUSTER</SMALL> when retrieving many rows from an
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index</li>
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<li>Use of<SMALL>LIMIT</SMALL> for returning a subset of a query's
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output</li>
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<li>Use of Prepared queries</li>
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<li>Use of<SMALL>ANALYZE</SMALL> to maintain accurate optimizer
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statistics</li>
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<li>Regular use of<SMALL>VACUUM</SMALL> or<I>pg_autovacuum</I>
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<li>Dropping of indexes during large data changes</li>
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</ul><BR>
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<BR>
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</DD>
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<DT><B>Server Configuration</B></DT>
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<DD>A number of<I>postgresql.conf</I> settings affect performance.
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For more details, see<ahref=
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"http://www.postgresql.org/docs/current/static/runtime.html">
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Administration Guide/Server Run-time Environment/Run-time Configuration</a>.
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You can disable<I>fsync()</I> by using<i>fsync</I> option. This will
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prevent<I>fsync()</I>s from flushing to disk after every
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transaction.</P>
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<P>You can use the<I>shared_buffers</I> option to
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increase the number of shared memory buffers used by the backend
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processes. If you make this parameter too high, the
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<I>postmaster</I> may not start because you have exceeded your
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kernel's limit on shared memory space. Each buffer is 8K and the
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default is 1000 buffers.</P>
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<P>You can also use the<I>sort_mem</I> (from PostgreSQL 8.0:<I>work_mem</I>)
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options to increase the maximum amount of memory used by the backend
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processes for each temporary sort. The default is 1024 (i.e. 1MB).</P>
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<P>You can also use the<SMALL>CLUSTER</SMALL> command to group
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data in tables to match an index. See the<SMALL>CLUSTER</SMALL>
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manual page for more details.</P>
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Administration Guide/Server Run-time Environment/Run-time
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Configuration</a> for a full listing, and for commentary see<a
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href="http://www.varlena.com/varlena/GeneralBits/Tidbits/annotated_conf_e.html">
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http://www.varlena.com/varlena/GeneralBits/Tidbits/annotated_conf_e.html</a>
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and<ahref="http://www.varlena.com/varlena/GeneralBits/Tidbits/perf.html">
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http://www.varlena.com/varlena/GeneralBits/Tidbits/perf.html</a>.
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<BR>
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<BR>
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</DD>
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<DT><B>Hardware Selection</B></DT>
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<DD>The effect of hardware on performance is detailed in<a
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href="http://candle.pha.pa.us/main/writings/pgsql/hw_performance/index.html">
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http://candle.pha.pa.us/main/writings/pgsql/hw_performance/index.html</a>.
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<BR>
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<BR>
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</DD>
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</DL>
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<H4><Aname="3.4">3.4</A>) What debugging features are
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available?</H4>
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compiler compute the dependencies automatically.</P>
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</BODY>
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</HTML>
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