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<!DOCTYPE html PUBLIC "-//W3C//DTD html 4.01 transitional//EN"> |
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> |
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<HTML> |
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<!-- DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2//EN" --> |
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<!-- HTML --> |
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<HEAD> |
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<META name="generator" content="HTML Tidy, see www.w3.org"> |
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<META http-equiv="Content-Type" content="text/html; charset=US-ASCII"> |
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<TITLE>PostgreSQL FAQ</TITLE> |
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</HEAD> |
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@ -14,7 +10,7 @@ |
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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: Sat Oct 19 22:58:02 EDT 2002</P> |
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<P>Last updated: Sun Oct 20 20:47:14 EDT 2002</P> |
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<P>Current maintainer: Bruce Momjian (<A href= |
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"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR> |
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@ -440,9 +436,8 @@ |
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<I>Features</I> section above. We are built for reliability and |
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features, though we continue to improve performance in every |
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release. There is an interesting Web page comparing PostgreSQL to |
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MySQL at <A href= "http://openacs.org/why-not-mysql.html"> |
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http://openacs.org/why-not-mysql.html</A><BR> |
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MySQL at <A href="http://openacs.org/philosophy/why-not-mysql.html"> |
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http://openacs.org/philosophy/why-not-mysql.html</A><BR> |
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<BR> |
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</DD> |
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@ -653,7 +648,7 @@ |
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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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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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@ -721,7 +716,7 @@ |
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<P>If <I>postmaster</I> is running, start <I>psql</I> in one |
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window, then find the <SMALL>PID</SMALL> of the <I>postgres</I> |
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process used by <I>psql</I>. Use a debugger to attach to the |
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<I>postgres</I> <SMALL>PID.</SMALL> You can set breakpoints in the |
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<I>postgres</I> <SMALL>PID</SMALL>. You can set breakpoints in the |
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debugger and issue queries from <I>psql</I>. If you are debugging |
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<I>postgres</I> startup, you can set PGOPTIONS="-W n", then start |
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<I>psql</I>. This will cause startup to delay for <I>n</I> seconds |
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@ -759,7 +754,7 @@ |
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maximum number of processes, <SMALL>NPROC;</SMALL> the maximum |
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number of processes per user, <SMALL>MAXUPRC;</SMALL> and the |
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maximum number of open files, <SMALL>NFILE</SMALL> and |
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<SMALL>NINODE.</SMALL> The reason that PostgreSQL has a limit on |
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<SMALL>NINODE</SMALL>. The reason that PostgreSQL has a limit on |
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the number of allowed backend processes is so your system won't run |
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out of resources.</P> |
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@ -768,14 +763,13 @@ |
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the MaxBackendId constant in |
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<I>include/storage/sinvaladt.h</I>.</P> |
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<H4><A name="3.9">3.9</A>) What are the <I>pgsql_tmp</I> |
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directory?</H4> |
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<H4><A name="3.9">3.9</A>) What is in the <I>pgsql_tmp</I> directory?</H4> |
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<P>They are temporary files generated by the query executor. For |
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example, if a sort needs to be done to satisfy an <SMALL>ORDER |
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BY,</SMALL> and the sort requires more space than the backend's |
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<I>-S</I> parameter allows, then temporary files are created to |
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hold the extra data.</P> |
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<P>This directory contains temporary files generated by the query |
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executor. For example, if a sort needs to be done to satisfy an |
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<SMALL>ORDER BY</SMALL> and the sort requires more space than the |
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backend's <I>-S</I> parameter allows, then temporary files are created |
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here to hold the extra data.</P> |
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<P>The temporary files are usually deleted automatically, but might |
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remain if a backend crashes during a sort. A stop and restart of the |
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@ -815,7 +809,7 @@ |
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<P>The entire query may have to be evaluated, even if you only want |
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the first few rows. Consider using a query that has an <SMALL>ORDER |
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BY.</SMALL> If there is an index that matches the <SMALL>ORDER |
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BY</SMALL>. If there is an index that matches the <SMALL>ORDER |
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BY</SMALL>, PostgreSQL may be able to evaluate only the first few |
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records requested, or the entire query may have to be evaluated |
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until the desired rows have been generated.</P> |
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@ -955,22 +949,22 @@ |
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</PRE> |
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<P>When using wild-card operators such as <SMALL>LIKE</SMALL> or |
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<I>~</I>, indexes can only be used in certain circumstances: |
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<I>~</I>, indexes can only be used in certain circumstances:</P> |
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<UL> |
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<LI>The beginning of the search string must be anchored to the start |
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of the string, i.e.:</LI> |
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of the string, i.e. |
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<UL> |
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<LI><SMALL>LIKE</SMALL> patterns must not start with <I>%.</I></LI> |
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<LI><SMALL>LIKE</SMALL> patterns must not start with <I>%</I>.</LI> |
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<LI><I>~</I> (regular expression) patterns must start with |
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<I>^.</I></LI> |
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</UL> |
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<I>^</I>.</LI> |
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</UL></LI> |
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<LI>The search string can not start with a character class, |
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e.g. [a-e].</LI> |
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<LI>Case-insensitive searches such as <SMALL>ILIKE</SMALL> and |
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<I>~*</I> do not utilise indexes. Instead, use functional |
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indexes, which are described in section <a href="#4.12">4.12</a>.</LI> |
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<LI>The default <I>C</I> locale must be used during |
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<i>initdb.</i></LI> |
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<i>initdb</i>.</LI> |
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</UL> |
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<P> |
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@ -1342,7 +1336,7 @@ BYTEA bytea variable-length byte array (null-byte safe) |
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Because PostgreSQL loads database-specific system catalogs, it is |
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uncertain how a cross-database query should even behave.</P> |
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<P><I>/contrib/dblink</I> allows cross-database queries using |
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<P><I>contrib/dblink</I> allows cross-database queries using |
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function calls. Of course, a client can make simultaneous |
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connections to different databases and merge the results on the |
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client side.</P> |
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@ -1379,13 +1373,13 @@ BYTEA bytea variable-length byte array (null-byte safe) |
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<H4><A name="4.28">4.28</A>) What encryption options are available? |
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</H4> |
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<UL> |
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<LI><I>/contrib/pgcrypto</I> contains many encryption functions for |
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<LI><I>contrib/pgcrypto</I> contains many encryption functions for |
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use in <SMALL>SQL</SMALL> queries.</LI> |
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<LI>The only way to encrypt transmission from the client to the |
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server is by using <I>hostssl</I> in <I>pg_hba.conf</I>.</LI> |
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<LI>Database user passwords are automatically encrypted when stored |
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in version 7.3. In previous versions, you must enable the option |
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<i>PASSWORD_ENCRYPTION</i> in <i>postgresql.conf</i>.</LI> |
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<I>PASSWORD_ENCRYPTION</I> in <I>postgresql.conf</I>.</LI> |
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<LI>The server can run using an encrypted file system.</LI> |
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</UL> |
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@ -1413,7 +1407,7 @@ BYTEA bytea variable-length byte array (null-byte safe) |
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functions are fully supported in C, PL/PgSQL, and SQL. See the |
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Programmer's Guide for more information. An example of a |
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table-returning function defined in C can be found in |
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contrib/tablefunc.</P> |
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<I>contrib/tablefunc</I>.</P> |
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<H4><A name="5.4">5.4</A>) I have changed a source file. Why does |
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the recompile not see the change?</H4> |
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Bruce Momjian
23 years ago