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Updates from Ian Barwick.

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Bruce Momjian
2002-10-21 00:47:44 +00:00
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doc/src/FAQ/FAQ.html
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<!DOCTYPE html PUBLIC "-//W3C//DTD html 4.01 transitional//EN">
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<HTML>
<!-- DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2//EN" -->
<!-- HTML -->
<HEAD>
<META name="generator" content="HTML Tidy, see www.w3.org">
<META http-equiv="Content-Type" content="text/html; charset=US-ASCII">
<TITLE>PostgreSQL FAQ</TITLE>
</HEAD>
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alink="#0000ff">
<H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1>
<P>Last updated: Sat Oct 19 22:58:02 EDT 2002</P>
<P>Last updated: Sun Oct 20 20:47:14 EDT 2002</P>
<P>Current maintainer: Bruce Momjian (<A href=
"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR>
@ -80,9 +76,9 @@
clients"</I> when trying to connect?<BR>
<A href="#3.9">3.9</A>) What is in the <I>pgsql_tmp</I>
directory?<BR>
<A href="#3.10">3.10</A>) Why do I need to do a dump and restore
<A href="#3.10">3.10</A>) Why do I need to do a dump and restore
to upgrade PostgreSQL releases?<BR>
<H2 align="center">Operational Questions</H2>
<A href="#4.1">4.1</A>) What is the difference between binary
@ -440,9 +436,8 @@
<I>Features</I> section above. We are built for reliability and
features, though we continue to improve performance in every
release. There is an interesting Web page comparing PostgreSQL to
MySQL at <A href= "http://openacs.org/why-not-mysql.html">
http://openacs.org/why-not-mysql.html</A><BR>
MySQL at <A href="http://openacs.org/philosophy/why-not-mysql.html">
http://openacs.org/philosophy/why-not-mysql.html</A><BR>
<BR>
</DD>
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<P>If you are doing many <SMALL>INSERTs</SMALL>, consider doing
them in a large batch using the <SMALL>COPY</SMALL> command. This
is much faster than individual <SMALL>INSERTS.</SMALL> Second,
is much faster than individual <SMALL>INSERTS</SMALL>. Second,
statements not in a <SMALL>BEGIN WORK/COMMIT</SMALL> transaction
block are considered to be in their own transaction. Consider
performing several statements in a single transaction block. This
@ -721,7 +716,7 @@
<P>If <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>. Use a debugger to attach to the
<I>postgres</I> <SMALL>PID.</SMALL> You can set breakpoints in the
<I>postgres</I> <SMALL>PID</SMALL>. You can set breakpoints in the
debugger and issue queries from <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
@ -759,7 +754,7 @@
maximum number of processes, <SMALL>NPROC;</SMALL> the maximum
number of processes per user, <SMALL>MAXUPRC;</SMALL> and the
maximum number of open files, <SMALL>NFILE</SMALL> and
<SMALL>NINODE.</SMALL> The reason that PostgreSQL has a limit on
<SMALL>NINODE</SMALL>. The reason that PostgreSQL has a limit on
the number of allowed backend processes is so your system won't run
out of resources.</P>
@ -768,14 +763,13 @@
the MaxBackendId constant in
<I>include/storage/sinvaladt.h</I>.</P>
<H4><A name="3.9">3.9</A>) What are the <I>pgsql_tmp</I>
directory?</H4>
<H4><A name="3.9">3.9</A>) What is in the <I>pgsql_tmp</I> directory?</H4>
<P>They are temporary files generated by the query executor. For
example, if a sort needs to be done to satisfy an <SMALL>ORDER
BY,</SMALL> and the sort requires more space than the backend's
<I>-S</I> parameter allows, then temporary files are created to
hold the extra data.</P>
<P>This directory contains temporary files generated by the query
executor. For example, if a sort needs to be done to satisfy an
<SMALL>ORDER BY</SMALL> and the sort requires more space than the
backend's <I>-S</I> parameter allows, then temporary files are created
here to hold the extra data.</P>
<P>The temporary files are usually deleted automatically, but might
remain if a backend crashes during a sort. A stop and restart of the
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<P>The entire query may have to be evaluated, even if you only want
the first few rows. Consider using a query that has an <SMALL>ORDER
BY.</SMALL> If there is an index that matches the <SMALL>ORDER
BY</SMALL>. If there is an index that matches the <SMALL>ORDER
BY</SMALL>, PostgreSQL may be able to evaluate only the first few
records requested, or the entire query may have to be evaluated
until the desired rows have been generated.</P>
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</PRE>
<P>When using wild-card operators such as <SMALL>LIKE</SMALL> or
<I>~</I>, indexes can only be used in certain circumstances:
<I>~</I>, indexes can only be used in certain circumstances:</P>
<UL>
<LI>The beginning of the search string must be anchored to the start
of the string, i.e.:</LI>
of the string, i.e.
<UL>
<LI><SMALL>LIKE</SMALL> patterns must not start with <I>%.</I></LI>
<LI><SMALL>LIKE</SMALL> patterns must not start with <I>%</I>.</LI>
<LI><I>~</I> (regular expression) patterns must start with
<I>^.</I></LI>
</UL>
<I>^</I>.</LI>
</UL></LI>
<LI>The search string can not start with a character class,
e.g. [a-e].</LI>
<LI>Case-insensitive searches such as <SMALL>ILIKE</SMALL> and
<I>~*</I> do not utilise indexes. Instead, use functional
indexes, which are described in section <a href="#4.12">4.12</a>.</LI>
<LI>The default <I>C</I> locale must be used during
<i>initdb.</i></LI>
<i>initdb</i>.</LI>
</UL>
<P>
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Because PostgreSQL loads database-specific system catalogs, it is
uncertain how a cross-database query should even behave.</P>
<P><I>/contrib/dblink</I> allows cross-database queries using
<P><I>contrib/dblink</I> allows cross-database queries using
function calls. Of course, a client can make simultaneous
connections to different databases and merge the results on the
client side.</P>
@ -1379,13 +1373,13 @@ BYTEA bytea variable-length byte array (null-byte safe)
<H4><A name="4.28">4.28</A>) What encryption options are available?
</H4>
<UL>
<LI><I>/contrib/pgcrypto</I> contains many encryption functions for
<LI><I>contrib/pgcrypto</I> contains many encryption functions for
use in <SMALL>SQL</SMALL> queries.</LI>
<LI>The only way to encrypt transmission from the client to the
server is by using <I>hostssl</I> in <I>pg_hba.conf</I>.</LI>
<LI>Database user passwords are automatically encrypted when stored
in version 7.3. In previous versions, you must enable the option
<i>PASSWORD_ENCRYPTION</i> in <i>postgresql.conf</i>.</LI>
<I>PASSWORD_ENCRYPTION</I> in <I>postgresql.conf</I>.</LI>
<LI>The server can run using an encrypted file system.</LI>
</UL>
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functions are fully supported in C, PL/PgSQL, and SQL. See the
Programmer's Guide for more information. An example of a
table-returning function defined in C can be found in
contrib/tablefunc.</P>
<I>contrib/tablefunc</I>.</P>
<H4><A name="5.4">5.4</A>) I have changed a source file. Why does
the recompile not see the change?</H4>