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Handle mixed-case names in reindex script.

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Document need for reindex in SGML docs.
REL7_3_STABLE
Bruce Momjian 24 years ago
parent a8a1f15877
commit 30be6c23c1
2 changed files with 114 additions and 101 deletions
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  1. 6
      contrib/reindex/reindex
  2. 209
      doc/src/sgml/maintenance.sgml

6
contrib/reindex/reindex
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@ -1,6 +1,6 @@
#!/bin/sh
# -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- #
# Package : reindexdb Version : $Revision: 1.2 $
# Package : reindexdb Version : $Revision: 1.3 $
# Date : 05/08/2002 Author : Shaun Thomas
# Req : psql, sh, perl, sed Type : Utility
#
@ -188,7 +188,7 @@ if [ "$index" ]; then
# Ok, no index. Is there a specific table to reindex?
elif [ "$table" ]; then
$PSQL $PSQLOPT $ECHOOPT -c "REINDEX TABLE $table" -d $dbname
$PSQL $PSQLOPT $ECHOOPT -c "REINDEX TABLE \"$table\"" -d $dbname
# No specific table, no specific index, either we have a specific database,
# or were told to do all databases. Do it!
@ -206,7 +206,7 @@ else
# database that we may reindex.
tables=`$PSQL $PSQLOPT -q -t -A -d $db -c "$sql"`
for tab in $tables; do
$PSQL $PSQLOPT $ECHOOPT -c "REINDEX TABLE $tab" -d $db
$PSQL $PSQLOPT $ECHOOPT -c "REINDEX TABLE \"$tab\"" -d $db
done
done

209
doc/src/sgml/maintenance.sgml
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@ -1,5 +1,5 @@
<!--
$Header: /cvsroot/pgsql/doc/src/sgml/maintenance.sgml,v 1.15 2002/06/22 04:08:07 momjian Exp $
$Header: /cvsroot/pgsql/doc/src/sgml/maintenance.sgml,v 1.16 2002/06/23 03:37:12 momjian Exp $
-->
<chapter id="maintenance">
@ -55,8 +55,8 @@ $Header: /cvsroot/pgsql/doc/src/sgml/maintenance.sgml,v 1.15 2002/06/22 04:08:07
</indexterm>
<para>
<productname>PostgreSQL</productname>'s <command>VACUUM</> command must be
run on a regular basis for several reasons:
<productname>PostgreSQL</productname>'s <command>VACUUM</> command
must be run on a regular basis for several reasons:
<orderedlist>
<listitem>
@ -100,26 +100,27 @@ $Header: /cvsroot/pgsql/doc/src/sgml/maintenance.sgml,v 1.15 2002/06/22 04:08:07
</indexterm>
<para>
In normal <productname>PostgreSQL</productname> operation, an <command>UPDATE</> or
<command>DELETE</> of a row does not immediately remove the old <firstterm>tuple</>
(version of the row). This approach is necessary to gain the benefits
of multiversion concurrency control (see the <citetitle>User's Guide</>):
the tuple must not be deleted while
it is still potentially visible to other transactions. But eventually,
an outdated or deleted tuple is no longer of interest to any transaction.
The space it occupies must be reclaimed for reuse by new tuples, to avoid
infinite growth of disk space requirements. This is done by running
<command>VACUUM</>.
In normal <productname>PostgreSQL</productname> operation, an
<command>UPDATE</> or <command>DELETE</> of a row does not
immediately remove the old <firstterm>tuple</> (version of the row).
This approach is necessary to gain the benefits of multiversion
concurrency control (see the <citetitle>User's Guide</>): the tuple
must not be deleted while it is still potentially visible to other
transactions. But eventually, an outdated or deleted tuple is no
longer of interest to any transaction. The space it occupies must be
reclaimed for reuse by new tuples, to avoid infinite growth of disk
space requirements. This is done by running <command>VACUUM</>.
</para>
<para>
Clearly, a table that receives frequent updates or deletes will need
to be vacuumed more often than tables that are seldom updated. It may
be useful to set up periodic <application>cron</> tasks that vacuum only selected tables,
skipping tables that are known not to change often. This is only likely
to be helpful if you have both large heavily-updated tables and large
seldom-updated tables --- the extra cost of vacuuming a small table
isn't enough to be worth worrying about.
to be vacuumed more often than tables that are seldom updated. It
may be useful to set up periodic <application>cron</> tasks that
vacuum only selected tables, skipping tables that are known not to
change often. This is only likely to be helpful if you have both
large heavily-updated tables and large seldom-updated tables --- the
extra cost of vacuuming a small table isn't enough to be worth
worrying about.
</para>
<para>
@ -174,18 +175,18 @@ $Header: /cvsroot/pgsql/doc/src/sgml/maintenance.sgml,v 1.15 2002/06/22 04:08:07
<para>
As with vacuuming for space recovery, frequent updates of statistics
are more useful for heavily-updated tables than for seldom-updated ones.
But even for a heavily-updated table, there may be no need for
statistics updates if the statistical distribution of the data is not
changing much. A simple rule of thumb is to think about how much
are more useful for heavily-updated tables than for seldom-updated
ones. But even for a heavily-updated table, there may be no need for
statistics updates if the statistical distribution of the data is
not changing much. A simple rule of thumb is to think about how much
the minimum and maximum values of the columns in the table change.
For example, a <type>timestamp</type> column that contains the time of row update
will have a constantly-increasing maximum value as rows are added and
updated; such a column will probably need more frequent statistics
updates than, say, a column containing URLs for pages accessed on a
website. The URL column may receive changes just as often, but the
statistical distribution of its values probably changes relatively
slowly.
For example, a <type>timestamp</type> column that contains the time
of row update will have a constantly-increasing maximum value as
rows are added and updated; such a column will probably need more
frequent statistics updates than, say, a column containing URLs for
pages accessed on a website. The URL column may receive changes just
as often, but the statistical distribution of its values probably
changes relatively slowly.
</para>
<para>
@ -247,42 +248,45 @@ $Header: /cvsroot/pgsql/doc/src/sgml/maintenance.sgml,v 1.15 2002/06/22 04:08:07
<para>
Prior to <productname>PostgreSQL</productname> 7.2, the only defense
against XID wraparound was to re-<command>initdb</> at least every 4 billion
transactions. This of course was not very satisfactory for high-traffic
sites, so a better solution has been devised. The new approach allows an
installation to remain up indefinitely, without <command>initdb</> or any sort of
restart. The price is this maintenance requirement:
<emphasis>every table in the database must be vacuumed at least once every
billion transactions</emphasis>.
against XID wraparound was to re-<command>initdb</> at least every 4
billion transactions. This of course was not very satisfactory for
high-traffic sites, so a better solution has been devised. The new
approach allows an installation to remain up indefinitely, without
<command>initdb</> or any sort of restart. The price is this
maintenance requirement: <emphasis>every table in the database must
be vacuumed at least once every billion transactions</emphasis>.
</para>
<para>
In practice this isn't an onerous requirement, but since the consequences
of failing to meet it can be complete data loss (not just wasted disk
space or slow performance), some special provisions have been made to help
database administrators keep track of the time since the last
<command>VACUUM</>. The remainder of this section gives the details.
In practice this isn't an onerous requirement, but since the
consequences of failing to meet it can be complete data loss (not
just wasted disk space or slow performance), some special provisions
have been made to help database administrators keep track of the
time since the last <command>VACUUM</>. The remainder of this
section gives the details.
</para>
<para>
The new approach to XID comparison distinguishes two special XIDs, numbers
1 and 2 (<literal>BootstrapXID</> and <literal>FrozenXID</>). These two
XIDs are always considered older than every normal XID. Normal XIDs (those
greater than 2) are compared using modulo-2<superscript>31</> arithmetic. This means
The new approach to XID comparison distinguishes two special XIDs,
numbers 1 and 2 (<literal>BootstrapXID</> and
<literal>FrozenXID</>). These two XIDs are always considered older
than every normal XID. Normal XIDs (those greater than 2) are
compared using modulo-2<superscript>31</> arithmetic. This means
that for every normal XID, there are two billion XIDs that are
<quote>older</> and two billion that are <quote>newer</>; another way to
say it is that the normal XID space is circular with no endpoint.
Therefore, once a tuple has been created with a particular normal XID, the
tuple will appear to be <quote>in the past</> for the next two billion
transactions, no matter which normal XID we are talking about. If the
tuple still exists after more than two billion transactions, it will
suddenly appear to be in the future. To prevent data loss, old tuples
must be reassigned the XID <literal>FrozenXID</> sometime before they reach
the two-billion-transactions-old mark. Once they are assigned this
special XID, they will appear to be <quote>in the past</> to all normal
transactions regardless of wraparound issues, and so such tuples will be
good until deleted, no matter how long that is. This reassignment of
XID is handled by <command>VACUUM</>.
<quote>older</> and two billion that are <quote>newer</>; another
way to say it is that the normal XID space is circular with no
endpoint. Therefore, once a tuple has been created with a particular
normal XID, the tuple will appear to be <quote>in the past</> for
the next two billion transactions, no matter which normal XID we are
talking about. If the tuple still exists after more than two billion
transactions, it will suddenly appear to be in the future. To
prevent data loss, old tuples must be reassigned the XID
<literal>FrozenXID</> sometime before they reach the
two-billion-transactions-old mark. Once they are assigned this
special XID, they will appear to be <quote>in the past</> to all
normal transactions regardless of wraparound issues, and so such
tuples will be good until deleted, no matter how long that is. This
reassignment of XID is handled by <command>VACUUM</>.
</para>
<para>
@ -346,21 +350,22 @@ VACUUM
<para>
<command>VACUUM</> with the <command>FREEZE</> option uses a more
aggressive freezing policy: tuples are frozen if they are old enough
to be considered good by all open transactions. In particular, if
a <command>VACUUM FREEZE</> is performed in an otherwise-idle database,
it is guaranteed that <emphasis>all</> tuples in that database will be
frozen. Hence, as long as the database is not modified in any way, it
will not need subsequent vacuuming to avoid transaction ID wraparound
problems. This technique is used by <filename>initdb</> to prepare the
<filename>template0</> database. It should also be used to prepare any
user-created databases that are to be marked <literal>datallowconn</> =
<literal>false</> in <filename>pg_database</>, since there isn't any
convenient way to vacuum a database that you can't connect to. Note
that <command>VACUUM</command>'s automatic warning message about unvacuumed databases will
ignore <filename>pg_database</> entries with <literal>datallowconn</> =
<literal>false</>, so as to avoid giving false warnings about these
databases; therefore it's up to you to ensure that such databases are
frozen correctly.
to be considered good by all open transactions. In particular, if a
<command>VACUUM FREEZE</> is performed in an otherwise-idle
database, it is guaranteed that <emphasis>all</> tuples in that
database will be frozen. Hence, as long as the database is not
modified in any way, it will not need subsequent vacuuming to avoid
transaction ID wraparound problems. This technique is used by
<filename>initdb</> to prepare the <filename>template0</> database.
It should also be used to prepare any user-created databases that
are to be marked <literal>datallowconn</> = <literal>false</> in
<filename>pg_database</>, since there isn't any convenient way to
vacuum a database that you can't connect to. Note that
<command>VACUUM</command>'s automatic warning message about
unvacuumed databases will ignore <filename>pg_database</> entries
with <literal>datallowconn</> = <literal>false</>, so as to avoid
giving false warnings about these databases; therefore it's up to
you to ensure that such databases are frozen correctly.
</para>
</sect2>
@ -375,13 +380,20 @@ VACUUM
</indexterm>
<para>
<productname>PostgreSQL</productname> is unable to reuse index pages
in some cases. The problem is that if indexed rows are deleted, those
indexes pages can only be reused by rows with similar values. In
cases where low indexed rows are deleted and newly inserted rows have
high values, disk space used by the index will grow indefinately, even
if <command>VACUUM</> is run frequently.
TO BE COMPLETED 2002-06-22 bjm
<productname>PostgreSQL</productname> is unable to reuse btree index
pages in certain cases. The problem is that if indexed rows are
deleted, those index pages can only be reused by rows with similar
values. For example, if indexed rows are deleted and newly
inserted/updated rows have much higher values, the new rows can't use
the index space made available by the deleted rows. Instead, such
new rows must be placed on new index pages. In such cases, disk
space used by the index will grow indefinately, even if
<command>VACUUM</> is run frequently.
</para>
<para>
As a solution, you can use the <command>REINDEX</> command
periodically to discard pages used by deleted rows. There is also
<filename>contrib/reindex</> which can reindex an entire database.
</para>
</sect1>
@ -404,31 +416,32 @@ VACUUM
</para>
<para>
If you simply direct the postmaster's <systemitem>stderr</> into a file, the only way
to truncate the log file is to stop and restart the postmaster. This
may be OK for development setups but you won't want to run a production
server that way.
If you simply direct the postmaster's <systemitem>stderr</> into a
file, the only way to truncate the log file is to stop and restart
the postmaster. This may be OK for development setups but you won't
want to run a production server that way.
</para>
<para>
The simplest production-grade approach to managing log output is to send it
all to <application>syslog</> and let <application>syslog</> deal with file
rotation. To do this, make sure <productname>PostgreSQL</> was built with
the <option>--enable-syslog</> configure option, and set
<literal>syslog</> to 2
(log to syslog only) in <filename>postgresql.conf</>.
Then you can send a <literal>SIGHUP</literal> signal to the
<application>syslog</> daemon whenever you want to force it to start
writing a new log file.
The simplest production-grade approach to managing log output is to
send it all to <application>syslog</> and let <application>syslog</>
deal with file rotation. To do this, make sure
<productname>PostgreSQL</> was built with the
<option>--enable-syslog</> configure option, and set
<literal>syslog</> to 2 (log to syslog only) in
<filename>postgresql.conf</>. Then you can send a
<literal>SIGHUP</literal> signal to the <application>syslog</> daemon
whenever you want to force it to start writing a new log file.
</para>
<para>
On many systems, however, syslog is not very reliable, particularly
with large log messages; it may truncate or drop messages just when
you need them the most. You may find it more useful to pipe the
<application>postmaster</>'s <systemitem>stderr</> to some type of log rotation script.
If you start the postmaster with <application>pg_ctl</>, then the
postmaster's <systemitem>stderr</> is already redirected to <systemitem>stdout</>, so you just need a
you need them the most. You may find it more useful to pipe the
<application>postmaster</>'s <systemitem>stderr</> to some type of
log rotation script. If you start the postmaster with
<application>pg_ctl</>, then the postmaster's <systemitem>stderr</>
is already redirected to <systemitem>stdout</>, so you just need a
pipe command:
<screen>

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