This patch makes some improvements and adds some additional detail
to the documentation on routine database maintainence activities. I also corrected a bunch of SGML markup.
This commit is contained in:
Neil Conway
parent
e24018728c
commit
0b52062265
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@ -1,5 +1,5 @@
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<!--
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$PostgreSQL: pgsql/doc/src/sgml/maintenance.sgml,v 1.29 2003/11/29 19:51:37 pgsql Exp $
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$PostgreSQL: pgsql/doc/src/sgml/maintenance.sgml,v 1.30 2003/12/14 00:10:32 neilc Exp $
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-->
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<chapter id="maintenance">
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@ -87,7 +87,7 @@ $PostgreSQL: pgsql/doc/src/sgml/maintenance.sgml,v 1.29 2003/11/29 19:51:37 pgsq
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of <command>VACUUM</> can run in parallel with normal database operations
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(selects, inserts, updates, deletes, but not changes to table definitions).
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Routine vacuuming is therefore not nearly as intrusive as it was in prior
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releases, and it's not as critical to try to schedule it at low-usage
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releases, and it is not as critical to try to schedule it at low-usage
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times of day.
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</para>
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@ -115,7 +115,7 @@ $PostgreSQL: pgsql/doc/src/sgml/maintenance.sgml,v 1.29 2003/11/29 19:51:37 pgsq
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Clearly, a table that receives frequent updates or deletes will need
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to be vacuumed more often than tables that are seldom updated. It
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may be useful to set up periodic <application>cron</> tasks that
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vacuum only selected tables, skipping tables that are known not to
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<command>VACUUM</command> only selected tables, skipping tables that are known not to
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change often. This is only likely to be helpful if you have both
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large heavily-updated tables and large seldom-updated tables --- the
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extra cost of vacuuming a small table isn't enough to be worth
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@ -123,39 +123,69 @@ $PostgreSQL: pgsql/doc/src/sgml/maintenance.sgml,v 1.29 2003/11/29 19:51:37 pgsq
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</para>
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<para>
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The standard form of <command>VACUUM</> is best used with the goal of
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maintaining a fairly level steady-state usage of disk space. The standard
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form finds old row versions and makes their space available for re-use within
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the table, but it does not try very hard to shorten the table file and
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return disk space to the operating system. If you need to return disk
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space to the operating system you can use <command>VACUUM FULL</> ---
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but what's the point of releasing disk space that will only have to be
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allocated again soon? Moderately frequent standard <command>VACUUM</> runs
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are a better approach than infrequent <command>VACUUM FULL</> runs for
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maintaining heavily-updated tables.
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There are two variants of the <command>VACUUM</command>
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command. The first form, known as <quote>lazy vacuum</quote> or
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just <command>VACUUM</command>, marks expired data in tables and
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indexes for future reuse; it does <emphasis>not</emphasis> attempt
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to reclaim the space used by this expired data
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immediately. Therefore, the table file is not shortened, and any
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unused space in the file is not returned to the operating
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system. This variant of <command>VACUUM</command> can be run
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concurrently with normal database operations.
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</para>
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<para>
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The second form is the <command>VACUUM FULL</command>
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command. This uses a more aggressive algorithm for reclaiming the
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space consumed by expired row versions. Any space that is freed by
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<command>VACUUM FULL</command> is immediately returned to the
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operating system. Unfortunately, this variant of the
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<command>VACUUM</command> command acquires an exclusive lock on
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each table while <command>VACUUM FULL</command> is processing
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it. Therefore, frequently using <command>VACUUM FULL</command> can
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have an extremely negative effect on the performance of concurrent
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database queries.
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</para>
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<para>
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The standard form of <command>VACUUM</> is best used with the goal
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of maintaining a fairly level steady-state usage of disk space. If
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you need to return disk space to the operating system you can use
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<command>VACUUM FULL</> --- but what's the point of releasing disk
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space that will only have to be allocated again soon? Moderately
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frequent standard <command>VACUUM</> runs are a better approach
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than infrequent <command>VACUUM FULL</> runs for maintaining
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heavily-updated tables.
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</para>
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<para>
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Recommended practice for most sites is to schedule a database-wide
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<command>VACUUM</> once a day at a low-usage time of day, supplemented
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by more frequent vacuuming of heavily-updated tables if necessary.
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(If you have multiple databases in a cluster, don't forget to
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vacuum each one; the program <filename>vacuumdb</> may be helpful.)
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Use plain <command>VACUUM</>, not <command>VACUUM FULL</>, for routine
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<command>VACUUM</> once a day at a low-usage time of day,
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supplemented by more frequent vacuuming of heavily-updated tables
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if necessary. In fact, some installations with an extremely high
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rate of data modification <command>VACUUM</command> some tables as
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often as once very five minutes. (If you have multiple databases
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in a cluster, don't forget to <command>VACUUM</command> each one;
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the program <filename>vacuumdb</> may be helpful.)
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</para>
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<para>
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<command>VACUUM FULL</> is recommended for cases where you know
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you have deleted the majority of rows in a table, so that the
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steady-state size of the table can be shrunk substantially with
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<command>VACUUM FULL</>'s more aggressive approach. Use plain
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<command>VACUUM</>, not <command>VACUUM FULL</>, for routine
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vacuuming for space recovery.
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</para>
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<para>
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<command>VACUUM FULL</> is recommended for cases where you know you have
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deleted the majority of rows in a table, so that the steady-state size
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of the table can be shrunk substantially with <command>VACUUM FULL</>'s
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more aggressive approach.
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</para>
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<para>
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If you have a table whose contents are deleted completely every so often,
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consider doing it with <command>TRUNCATE</> rather than using
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<command>DELETE</> followed by <command>VACUUM</>.
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If you have a table whose contents are deleted on a periodic
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basis, consider doing it with <command>TRUNCATE</command> rather
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than using <command>DELETE</command> followed by
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<command>VACUUM</command>. <command>TRUNCATE</command> removes the
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entire content of the table immediately, without recquiring a
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subsequent <command>VACUUM</command> or <command>VACUUM
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FULL</command> to reclaim the now-unused disk space.
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</para>
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</sect2>
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@ -319,7 +349,7 @@ $PostgreSQL: pgsql/doc/src/sgml/maintenance.sgml,v 1.29 2003/11/29 19:51:37 pgsq
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statistics in the system table <literal>pg_database</>. In particular,
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the <literal>datfrozenxid</> column of a database's
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<literal>pg_database</> row is updated at the completion of any
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database-wide vacuum operation (i.e., <command>VACUUM</> that does not
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database-wide <command>VACUUM</command> operation (i.e., <command>VACUUM</> that does not
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name a specific table). The value stored in this field is the freeze
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cutoff XID that was used by that <command>VACUUM</> command. All normal
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XIDs older than this cutoff XID are guaranteed to have been replaced by
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@ -338,7 +368,7 @@ SELECT datname, age(datfrozenxid) FROM pg_database;
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With the standard freezing policy, the <literal>age</> column will start
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at one billion for a freshly-vacuumed database. When the <literal>age</>
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approaches two billion, the database must be vacuumed again to avoid
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risk of wraparound failures. Recommended practice is to vacuum each
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risk of wraparound failures. Recommended practice is to <command>VACUUM</command> each
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database at least once every half-a-billion (500 million) transactions,
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so as to provide plenty of safety margin. To help meet this rule,
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each database-wide <command>VACUUM</> automatically delivers a warning
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@ -366,7 +396,7 @@ VACUUM
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It should also be used to prepare any user-created databases that
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are to be marked <literal>datallowconn</> = <literal>false</> in
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<literal>pg_database</>, since there isn't any convenient way to
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vacuum a database that you can't connect to. Note that
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<command>VACUUM</command> a database that you can't connect to. Note that
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<command>VACUUM</command>'s automatic warning message about
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unvacuumed databases will ignore <literal>pg_database</> entries
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with <literal>datallowconn</> = <literal>false</>, so as to avoid
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@ -404,20 +434,22 @@ VACUUM
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</indexterm>
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<para>
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It's a good idea to save the database server's log output somewhere,
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rather than just routing it to <filename>/dev/null</>. The log output
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is invaluable when it comes time to diagnose problems. However, the
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log output tends to be voluminous (especially at higher debug levels)
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and you won't want to save it indefinitely. You need to <quote>rotate</>
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the log files so that new log files are started and old ones thrown
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away every so often.
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It is a good idea to save the database server's log output
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somewhere, rather than just routing it to <filename>/dev/null</>.
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The log output is invaluable when it comes time to diagnose
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problems. However, the log output tends to be voluminous
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(especially at higher debug levels) and you won't want to save it
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indefinitely. You need to <quote>rotate</> the log files so that
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new log files are started and old ones removed after a reasonable
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period of time.
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</para>
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<para>
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If you simply direct the <systemitem>stderr</> of the <command>postmaster</command> into a
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file, the only way to truncate the log file is to stop and restart
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the <command>postmaster</command>. This may be OK for development setups but you won't
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want to run a production server that way.
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the <command>postmaster</command>. This may be OK if you are using
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<productname>PostgreSQL</productname> in a development environment,
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but few production servers would find this behavior acceptable.
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</para>
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<para>
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@ -444,14 +476,16 @@ VACUUM
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<command>pg_ctl</>, then the <systemitem>stderr</> of the <command>postmaster</command>
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is already redirected to <systemitem>stdout</>, so you just need a
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pipe command:
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<programlisting>
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pg_ctl start | logrotate
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</programlisting>
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The <productname>PostgreSQL</> distribution doesn't include a suitable
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log rotation program, but there are many available on the Internet;
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one is included in the Apache distribution, for example.
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The <productname>PostgreSQL</> distribution doesn't include a
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suitable log rotation program, but there are many available on the
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Internet. For example, the <application>logrotate</application>
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tool included in the <productname>Apache</productname> distribution
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can be used with <productname>PostgreSQL</productname>.
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</para>
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</sect1>
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</chapter>
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@ -1,5 +1,5 @@
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<!--
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$PostgreSQL: pgsql/doc/src/sgml/page.sgml,v 1.16 2003/11/29 19:51:37 pgsql Exp $
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$PostgreSQL: pgsql/doc/src/sgml/page.sgml,v 1.17 2003/12/14 00:10:32 neilc Exp $
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-->
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<chapter id="page">
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@ -151,7 +151,8 @@ data. Empty in ordinary tables.</entry>
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</table>
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<para>
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All the details may be found in src/include/storage/bufpage.h.
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All the details may be found in
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<filename>src/include/storage/bufpage.h</filename>.
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</para>
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<para>
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@ -305,7 +306,8 @@ data. Empty in ordinary tables.</entry>
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</table>
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<para>
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All the details may be found in src/include/access/htup.h.
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All the details may be found in
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<filename>src/include/access/htup.h</filename>.
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</para>
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<para>
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@ -1,5 +1,5 @@
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<!--
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$PostgreSQL: pgsql/doc/src/sgml/perform.sgml,v 1.38 2003/11/29 19:51:37 pgsql Exp $
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$PostgreSQL: pgsql/doc/src/sgml/perform.sgml,v 1.39 2003/12/14 00:10:32 neilc Exp $
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-->
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<chapter id="performance-tips">
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@ -100,7 +100,7 @@ $PostgreSQL: pgsql/doc/src/sgml/perform.sgml,v 1.38 2003/11/29 19:51:37 pgsql Ex
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<para>
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Here are some examples (using the regression test database after a
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<literal>VACUUM ANALYZE</>, and 7.3 development sources):
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<command>VACUUM ANALYZE</>, and 7.3 development sources):
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<programlisting>
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EXPLAIN SELECT * FROM tenk1;
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@ -1,5 +1,5 @@
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<!--
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$PostgreSQL: pgsql/doc/src/sgml/plperl.sgml,v 2.21 2003/11/29 19:51:37 pgsql Exp $
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$PostgreSQL: pgsql/doc/src/sgml/plperl.sgml,v 2.22 2003/12/14 00:10:32 neilc Exp $
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-->
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<chapter id="plperl">
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@ -152,7 +152,7 @@ SELECT name, empcomp(employee) FROM employee;
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<para>
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The argument values supplied to a PL/Perl function's code are
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simply the input arguments converted to text form (just as if they
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had been displayed by a <literal>SELECT</literal> statement).
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had been displayed by a <command>SELECT</command> statement).
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Conversely, the <literal>return</> command will accept any string
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that is acceptable input format for the function's declared return
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type. So, the PL/Perl programmer can manipulate data values as if
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@ -1,4 +1,4 @@
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<!-- $PostgreSQL: pgsql/doc/src/sgml/protocol.sgml,v 1.48 2003/11/29 19:51:37 pgsql Exp $ -->
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<!-- $PostgreSQL: pgsql/doc/src/sgml/protocol.sgml,v 1.49 2003/12/14 00:10:32 neilc Exp $ -->
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<chapter id="protocol">
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<title>Frontend/Backend Protocol</title>
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@ -200,13 +200,13 @@
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<para>
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This section describes the message flow and the semantics of each
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message type. (Details of the exact representation of each message
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appear in <xref linkend="protocol-message-formats">.)
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There are several different sub-protocols
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depending on the state of the connection: start-up,
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query, function call, COPY, and termination. There are also special
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provisions for asynchronous operations (including
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notification responses and command cancellation),
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which can occur at any time after the start-up phase.
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appear in <xref linkend="protocol-message-formats">.) There are
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several different sub-protocols depending on the state of the
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connection: start-up, query, function call,
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<command>COPY</command>, and termination. There are also special
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provisions for asynchronous operations (including notification
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responses and command cancellation), which can occur at any time
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after the start-up phase.
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</para>
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<sect2>
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@ -989,15 +989,17 @@
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</para>
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<para>
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ParameterStatus messages will be generated whenever the active value
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changes for any of the parameters the backend believes the frontend
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should know about. Most commonly this occurs in response to a
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<command>SET</> SQL command executed by the frontend, and this case
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is effectively synchronous --- but it is also possible for parameter
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status changes to occur because the administrator changed a configuration
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file and then sent the <systemitem>SIGHUP</systemitem> signal to the postmaster. Also, if a SET command is
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rolled back, an appropriate ParameterStatus message will be generated
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to report the current effective value.
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ParameterStatus messages will be generated whenever the active
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value changes for any of the parameters the backend believes the
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frontend should know about. Most commonly this occurs in response
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to a <command>SET</> SQL command executed by the frontend, and
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this case is effectively synchronous --- but it is also possible
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for parameter status changes to occur because the administrator
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changed a configuration file and then sent the
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<systemitem>SIGHUP</systemitem> signal to the postmaster. Also,
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if a <command>SET</command> command is rolled back, an appropriate
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ParameterStatus message will be generated to report the current
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effective value.
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</para>
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<para>
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@ -1129,46 +1131,53 @@
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<para>
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For either normal or abnormal termination, any open transaction is
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rolled back, not committed. One should note however that if a
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frontend disconnects while a non-SELECT query is being processed,
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the backend will probably finish the query before noticing the
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disconnection.
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If the query is outside any transaction block (<command>BEGIN</>
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... <command>COMMIT</> sequence) then its results may be committed
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before the disconnection is recognized.
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frontend disconnects while a non-<command>SELECT</command> query
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is being processed, the backend will probably finish the query
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before noticing the disconnection. If the query is outside any
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transaction block (<command>BEGIN</> ... <command>COMMIT</>
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sequence) then its results may be committed before the
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disconnection is recognized.
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</para>
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</sect2>
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<Sect2>
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<Title>SSL Session Encryption</Title>
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<Title><acronym>SSL</acronym> Session Encryption</Title>
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<Para>
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If <productname>PostgreSQL</> was built with SSL support, frontend/backend
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communications can be encrypted using SSL. This provides communication
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security in environments where attackers might be able to capture the
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session traffic.
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If <productname>PostgreSQL</> was built with
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<acronym>SSL</acronym> support, frontend/backend communications
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can be encrypted using <acronym>SSL</acronym>. This provides
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communication security in environments where attackers might be
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able to capture the session traffic. For more information on
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encrypting <productname>PostgreSQL</productname> sessions with
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<acronym>SSL</acronym>, see <xref linkend="ssl-tcp">.
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</para>
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<para>
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To initiate an SSL-encrypted connection, the frontend initially sends
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an SSLRequest message rather than a StartupMessage. The server then
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responds with a single byte containing <literal>S</> or <literal>N</>,
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indicating that it is willing or unwilling to perform SSL, respectively.
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The frontend may close the connection at this point if it is dissatisfied
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with the response. To continue after <literal>S</>, perform an SSL
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startup handshake (not described here, part of the SSL specification)
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with the server. If this is successful, continue with
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sending the usual StartupMessage. In this case the StartupMessage and
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all subsequent data will be SSL-encrypted. To continue after
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To initiate an <acronym>SSL</acronym>-encrypted connection, the
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frontend initially sends an SSLRequest message rather than a
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StartupMessage. The server then responds with a single byte
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containing <literal>S</> or <literal>N</>, indicating that it is
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willing or unwilling to perform <acronym>SSL</acronym>,
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respectively. The frontend may close the connection at this point
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if it is dissatisfied with the response. To continue after
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<literal>S</>, perform an <acronym>SSL</acronym> startup handshake
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(not described here, part of the <acronym>SSL</acronym>
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specification) with the server. If this is successful, continue
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with sending the usual StartupMessage. In this case the
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StartupMessage and all subsequent data will be
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<acronym>SSL</acronym>-encrypted. To continue after
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<literal>N</>, send the usual StartupMessage and proceed without
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||||
encryption.
|
||||
</para>
|
||||
|
||||
<para>
|
||||
The frontend should also be prepared to handle an ErrorMessage response
|
||||
to SSLRequest from the server. This would only occur if the server
|
||||
predates the addition of SSL support to <productname>PostgreSQL</>.
|
||||
In this case the connection must be closed, but the frontend may choose
|
||||
to open a fresh connection and proceed without requesting SSL.
|
||||
The frontend should also be prepared to handle an ErrorMessage
|
||||
response to SSLRequest from the server. This would only occur if
|
||||
the server predates the addition of <acronym>SSL</acronym> support
|
||||
to <productname>PostgreSQL</>. In this case the connection must
|
||||
be closed, but the frontend may choose to open a fresh connection
|
||||
and proceed without requesting <acronym>SSL</acronym>.
|
||||
</para>
|
||||
|
||||
<para>
|
||||
|
|
@ -1178,8 +1187,9 @@
|
|||
|
||||
<para>
|
||||
While the protocol itself does not provide a way for the server to
|
||||
force SSL encryption, the administrator may configure the server to
|
||||
reject unencrypted sessions as a byproduct of authentication checking.
|
||||
force <acronym>SSL</acronym> encryption, the administrator may
|
||||
configure the server to reject unencrypted sessions as a byproduct
|
||||
of authentication checking.
|
||||
</para>
|
||||
</sect2>
|
||||
</sect1>
|
||||
|
|
@ -2106,7 +2116,7 @@ CopyData (F & B)
|
|||
</Term>
|
||||
<ListItem>
|
||||
<Para>
|
||||
Identifies the message as COPY data.
|
||||
Identifies the message as <command>COPY</command> data.
|
||||
</Para>
|
||||
</ListItem>
|
||||
</VarListEntry>
|
||||
|
|
@ -2153,7 +2163,7 @@ CopyDone (F & B)
|
|||
</Term>
|
||||
<ListItem>
|
||||
<Para>
|
||||
Identifies the message as a COPY-complete indicator.
|
||||
Identifies the message as a <command>COPY</command>-complete indicator.
|
||||
</Para>
|
||||
</ListItem>
|
||||
</VarListEntry>
|
||||
|
|
@ -2188,7 +2198,7 @@ CopyFail (F)
|
|||
</Term>
|
||||
<ListItem>
|
||||
<Para>
|
||||
Identifies the message as a COPY-failure indicator.
|
||||
Identifies the message as a <command>COPY</command>-failure indicator.
|
||||
</Para>
|
||||
</ListItem>
|
||||
</VarListEntry>
|
||||
|
|
@ -2255,7 +2265,7 @@ CopyInResponse (B)
|
|||
</Term>
|
||||
<ListItem>
|
||||
<Para>
|
||||
0 indicates the overall copy format is textual (rows
|
||||
0 indicates the overall <command>COPY</command> format is textual (rows
|
||||
separated by newlines, columns separated by separator
|
||||
characters, etc).
|
||||
1 indicates the overall copy format is binary (similar
|
||||
|
|
@ -2330,13 +2340,12 @@ CopyOutResponse (B)
|
|||
</Term>
|
||||
<ListItem>
|
||||
<Para>
|
||||
0 indicates the overall copy format is textual (rows
|
||||
separated by newlines, columns separated by separator
|
||||
characters, etc).
|
||||
1 indicates the overall copy format is binary (similar
|
||||
to DataRow format).
|
||||
See <xref linkend="sql-copy" endterm="sql-copy-title">
|
||||
for more information.
|
||||
0 indicates the overall <command>COPY</command> format
|
||||
is textual (rows separated by newlines, columns
|
||||
separated by separator characters, etc). 1 indicates
|
||||
the overall copy format is binary (similar to DataRow
|
||||
format). See <xref linkend="sql-copy"
|
||||
endterm="sql-copy-title"> for more information.
|
||||
</Para>
|
||||
</ListItem>
|
||||
</VarListEntry>
|
||||
|
|
@ -3602,7 +3611,7 @@ SSLRequest (F)
|
|||
</Term>
|
||||
<ListItem>
|
||||
<Para>
|
||||
The SSL request code. The value is chosen to contain
|
||||
The <acronym>SSL</acronym> request code. The value is chosen to contain
|
||||
<literal>1234</> in the most significant 16 bits, and <literal>5679</> in the
|
||||
least 16 significant bits. (To avoid confusion, this code
|
||||
must not be the same as any protocol version number.)
|
||||
|
|
@ -3899,8 +3908,9 @@ message.
|
|||
<ListItem>
|
||||
<Para>
|
||||
Where: an indication of the context in which the error occurred.
|
||||
Presently this includes a call stack traceback of active PL functions.
|
||||
The trace is one entry per line, most recent first.
|
||||
Presently this includes a call stack traceback of active
|
||||
procedural language functions. The trace is one entry per line,
|
||||
most recent first.
|
||||
</Para>
|
||||
</ListItem>
|
||||
</VarListEntry>
|
||||
|
|
@ -4006,12 +4016,12 @@ may allow improvements in performance or functionality.
|
|||
</para>
|
||||
|
||||
<para>
|
||||
COPY data is now encapsulated into CopyData and CopyDone messages. There
|
||||
is a well-defined way to recover from errors during COPY. The special
|
||||
<command>COPY</command> data is now encapsulated into CopyData and CopyDone messages. There
|
||||
is a well-defined way to recover from errors during <command>COPY</command>. The special
|
||||
<quote><literal>\.</></quote> last line is not needed anymore, and is not sent
|
||||
during COPY OUT.
|
||||
(It is still recognized as a terminator during COPY IN, but its use is
|
||||
deprecated and will eventually be removed.) Binary COPY is supported.
|
||||
during <command>COPY OUT</command>.
|
||||
(It is still recognized as a terminator during <command>COPY IN</command>, but its use is
|
||||
deprecated and will eventually be removed.) Binary <command>COPY</command> is supported.
|
||||
The CopyInResponse and CopyOutResponse messages include fields indicating
|
||||
the number of columns and the format of each column.
|
||||
</para>
|
||||
|
|
@ -4046,7 +4056,7 @@ the backend.
|
|||
<para>
|
||||
The NotificationResponse ('<literal>A</>') message has an additional string
|
||||
field, which is presently empty but may someday carry additional data passed
|
||||
from the NOTIFY event sender.
|
||||
from the <command>NOTIFY</command> event sender.
|
||||
</para>
|
||||
|
||||
<para>
|
||||
|
|
|
|||
|
|
@ -1,5 +1,5 @@
|
|||
<!--
|
||||
$PostgreSQL: pgsql/doc/src/sgml/typeconv.sgml,v 1.41 2003/12/02 00:26:59 tgl Exp $
|
||||
$PostgreSQL: pgsql/doc/src/sgml/typeconv.sgml,v 1.42 2003/12/14 00:10:32 neilc Exp $
|
||||
-->
|
||||
|
||||
<chapter Id="typeconv">
|
||||
|
|
@ -122,9 +122,9 @@ with, and perhaps converted to, the types of the target columns.
|
|||
</term>
|
||||
<listitem>
|
||||
<para>
|
||||
Since all query results from a unionized <literal>SELECT</literal> statement
|
||||
Since all query results from a unionized <command>SELECT</command> statement
|
||||
must appear in a single set of columns, the types of the results of each
|
||||
<literal>SELECT</> clause must be matched up and converted to a uniform set.
|
||||
<command>SELECT</> clause must be matched up and converted to a uniform set.
|
||||
Similarly, the branch expressions of a <literal>CASE</> construct must be
|
||||
converted to a common type so that the <literal>CASE</> expression as a whole
|
||||
has a known output type. The same holds for <literal>ARRAY</> constructs.
|
||||
|
|
|
|||
Loading…
Reference in a new issue