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提交 189c3481 编写于 作者: B Bruce Momjian
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doc/FAQ
浏览文件 @ 189c3481
Frequently Asked Questions (FAQ) for PostgreSQL
Last updated: Sat Oct 19 22:58:02 EDT 2002
Last updated: Sun Oct 20 20:47:14 EDT 2002
Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
......@@ -339,7 +339,7 @@
the Features 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 http://openacs.org/why-not-mysql.html
to MySQL at http://openacs.org/philosophy/why-not-mysql.html
Reliability
We realize that a DBMS must be reliable, or it is worthless. We
......@@ -596,12 +596,12 @@
was 64, and changing it required a rebuild after altering the
MaxBackendId constant in include/storage/sinvaladt.h.
3.9) What are the pgsql_tmp directory?
3.9) What is in the pgsql_tmp directory?
They are temporary files generated by the query executor. For example,
if a sort needs to be done to satisfy an ORDER BY, and the sort
requires more space than the backend's -S parameter allows, then
temporary files are created to hold the extra data.
This directory contains temporary files generated by the query
executor. For example, if a sort needs to be done to satisfy an ORDER
BY and the sort requires more space than the backend's -S parameter
allows, then temporary files are created here to hold the extra data.
The temporary files are usually deleted automatically, but might
remain if a backend crashes during a sort. A stop and restart of the
......@@ -758,19 +758,16 @@
When using wild-card operators such as LIKE or ~, indexes can only be
used in certain circumstances:
* The beginning of the search string must be anchored to the start
of the string, i.e.:
of the string, i.e.
+ LIKE patterns must not start with %.
+ ~ (regular expression) patterns must start with ^.
* The search string can not start with a character class, e.g.
[a-e].
* Case-insensitive searches such as ILIKE and ~* do not utilise
indexes. Instead, use functional indexes, which are described in
section 4.12.
* The default C locale must be used during initdb.
* LIKE patterns must not start with %.
* ~ (regular expression) patterns must start with ^.
The search string can not start with a character class, e.g. [a-e].
Case-insensitive searches such as ILIKE and ~* do not utilise
indexes. Instead, use functional indexes, which are described in
section 4.12.
The default C locale must be used during initdb.
4.9) How do I see how the query optimizer is evaluating my query?
See the EXPLAIN manual page.
......@@ -1057,7 +1054,7 @@ CREATE TABLE test (x int, modtime timestamp DEFAULT CURRENT_TIMESTAMP );
Because PostgreSQL loads database-specific system catalogs, it is
uncertain how a cross-database query should even behave.
/contrib/dblink allows cross-database queries using function calls. Of
contrib/dblink 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.
......@@ -1089,8 +1086,8 @@ CREATE TABLE test (x int, modtime timestamp DEFAULT CURRENT_TIMESTAMP );
4.28) What encryption options are available?
* /contrib/pgcrypto contains many encryption functions for use in
SQL queries.
* contrib/pgcrypto contains many encryption functions for use in SQL
queries.
* The only way to encrypt transmission from the client to the server
is by using hostssl in pg_hba.conf.
* Database user passwords are automatically encrypted when stored in
......
doc/src/FAQ/FAQ.html
浏览文件 @ 189c3481
<!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>
......@@ -14,7 +10,7 @@
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>
......@@ -653,7 +648,7 @@
<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
......@@ -815,7 +809,7 @@
<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>
......@@ -955,22 +949,22 @@
</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>
......@@ -1342,7 +1336,7 @@ BYTEA bytea variable-length byte array (null-byte safe)
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>
......@@ -1413,7 +1407,7 @@ BYTEA bytea variable-length byte array (null-byte safe)
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>
......
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