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This patch makes a number of improvements to the runtime config

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documentation.

Neil Conway
This commit is contained in:
Bruce Momjian 2003-09-11 17:27:38 +00:00
parent ab19254618
commit 64a7b58aa0
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doc/src/sgml/runtime.sgml
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@ -1,5 +1,5 @@
<!--
$Header: /cvsroot/pgsql/doc/src/sgml/runtime.sgml,v 1.204 2003/09/07 15:26:45 tgl Exp $
$Header: /cvsroot/pgsql/doc/src/sgml/runtime.sgml,v 1.205 2003/09/11 17:27:38 momjian Exp $
-->
<Chapter Id="runtime">
@ -448,14 +448,15 @@ psql: could not connect to server: Connection refused
</indexterm>
<para>
There are a lot of configuration parameters that affect the behavior
of the database system. Here we describe how to set them and the
following subsections will discuss each in detail.
There are a lot of configuration parameters that affect the
behavior of the database system. In this subsection, we describe
how to set configuration parameters; the following subsections
discuss each parameter in detail.
</para>
<para>
All parameter names are case-insensitive. Every parameter takes a
value of one of the four types: Boolean, integer, floating point,
value of one of the four types: boolean, integer, floating point,
and string. Boolean values are <literal>ON</literal>,
<literal>OFF</literal>, <literal>TRUE</literal>,
<literal>FALSE</literal>, <literal>YES</literal>,
@ -465,18 +466,18 @@ psql: could not connect to server: Connection refused
<para>
One way to set these options is to edit the file
<filename>postgresql.conf</filename><indexterm><primary>postgresql.conf</></> in the data directory. (A
default file is installed there.) An example of what this file might
look like is:
<filename>postgresql.conf</filename><indexterm><primary>postgresql.conf</></>
in the data directory. (A default file is installed there.) An
example of what this file might look like is:
<programlisting>
# This is a comment
log_connections = yes
syslog = 2
search_path = '$user, public'
</programlisting>
As you see, options are one per line. The equal sign between name
and value is optional. Whitespace is insignificant and blank lines
are ignored. Hash marks (<literal>#</literal>) introduce comments
One option is specified per line. The equal sign between name and
value is optional. Whitespace is insignificant and blank lines are
ignored. Hash marks (<literal>#</literal>) introduce comments
anywhere. Parameter values that are not simple identifiers or
numbers should be single-quoted.
</para>
@ -485,12 +486,14 @@ search_path = '$user, public'
<indexterm>
<primary>SIGHUP</primary>
</indexterm>
The configuration file is reread whenever the <command>postmaster</command> process receives a
<systemitem>SIGHUP</> signal (which is most easily sent by means of
<literal>pg_ctl reload</>). The <command>postmaster</command> also propagates this
signal to all currently running server processes so that existing
sessions also get the new value. Alternatively, you can send the
signal to a single server process directly.
The configuration file is reread whenever the
<command>postmaster</command> process receives a
<systemitem>SIGHUP</> signal (which is most easily sent by means
of <literal>pg_ctl reload</>). The <command>postmaster</command>
also propagates this signal to all currently running server
processes so that existing sessions also get the new
value. Alternatively, you can send the signal to a single server
process directly.
</para>
<para>
@ -518,20 +521,21 @@ env PGOPTIONS='-c geqo=off' psql
</para>
<para>
Some options can be changed in individual SQL sessions with the
<command>SET</command> command, for example:
Some options can be changed in individual <acronym>SQL</acronym>
sessions with the <command>SET</command> command, for example:
<screen>
SET ENABLE_SEQSCAN TO OFF;
</screen>
See the SQL command language reference for details on the syntax.
See the <acronym>SQL</acronym> command language reference for
details on the syntax.
</para>
<para>
Furthermore, it is possible to assign a set of option settings to
a user or a database. Whenever a session is started, the default
settings for the user and database involved are loaded. The
commands <literal>ALTER DATABASE</literal> and <literal>ALTER
USER</literal>, respectively, are used to configure these
commands <command>ALTER DATABASE</command> and <command>ALTER
USER</command>, respectively, are used to configure these
settings. Such per-database settings override anything received
from the <command>postmaster</command> command-line or the
configuration file, and in turn are overridden by per-user
@ -643,9 +647,9 @@ SET ENABLE_SEQSCAN TO OFF;
<para>
Determines the maximum number of concurrent connections to the
database server. The default is typically 100, but may be less
if your kernel settings will not support it (as determined
during <application>initdb</>).
This parameter can only be set at server start.
if your kernel settings will not support it (as determined
during <application>initdb</>). This parameter can only be
set at server start.
</para>
<para>
@ -665,16 +669,16 @@ SET ENABLE_SEQSCAN TO OFF;
<para>
Determines the number of <quote>connection slots</quote> that
are reserved for connections by <productname>PostgreSQL</>
superusers. At most <varname>max_connections</> connections can
superusers. At most <varname>MAX_CONNECTIONS</> connections can
ever be active simultaneously. Whenever the number of active
concurrent connections is at least <varname>max_connections</> minus
<varname>superuser_reserved_connections</varname>, new connections
concurrent connections is at least <varname>MAX_CONNECTIONS</> minus
<varname>SUPERUSER_RESERVED_CONNECTIONS</varname>, new connections
will be accepted only for superusers.
</para>
<para>
The default value is 2. The value must be less than the value of
<varname>max_connections</varname>. This parameter can only be
<varname>MAX_CONNECTIONS</varname>. This parameter can only be
set at server start.
</para>
</listitem>
@ -874,7 +878,7 @@ SET ENABLE_SEQSCAN TO OFF;
</sect2>
<sect2 id="runtime-config-resource">
<title>Resource Usage (Except WAL)</title>
<title>Resource Consumption</title>
<sect3 id="runtime-config-resource-memory">
<title>Memory</title>
@ -885,16 +889,16 @@ SET ENABLE_SEQSCAN TO OFF;
<listitem>
<para>
Sets the number of shared memory buffers used by the database
server. The default is typically 1000, but may be less
if your kernel settings will not support it (as determined
during <application>initdb</>). Each buffer is 8192
bytes, unless a different value of <literal>BLCKSZ</> was chosen
when building the server. This setting must be at least 16,
as well as at least twice the value of
<varname>MAX_CONNECTIONS</varname>; however, settings significantly
higher than the minimum are usually needed for good performance.
Values of a few thousand are recommended for production installations.
This option can only be set at server start.
server. The default is typically 1000, but may be less if your
kernel settings will not support it (as determined during
<application>initdb</>). Each buffer is 8192 bytes, unless a
different value of <literal>BLCKSZ</> was chosen when building
the server. This setting must be at least 16, as well as at
least twice the value of <varname>MAX_CONNECTIONS</varname>;
however, settings significantly higher than the minimum are
usually needed for good performance. Values of a few thousand
are recommended for production installations. This option can
only be set at server start.
</para>
<para>
@ -924,7 +928,7 @@ SET ENABLE_SEQSCAN TO OFF;
Hash tables are used in hash joins, hash-based aggregation, and
hash-based processing of <literal>IN</> subqueries. Because
<command>CREATE INDEX</> is used when restoring a database, it might
be good to temporary increase this value during a restore.
be good to temporarily increase this value during a restore.
</para>
</listitem>
</varlistentry>
@ -955,7 +959,7 @@ SET ENABLE_SEQSCAN TO OFF;
Sets the maximum number of disk pages for which free space will
be tracked in the shared free-space map. Six bytes of shared memory
are consumed for each page slot. This setting must be more than
16 * <varname>max_fsm_relations</varname>. The default is 20000.
16 * <varname>MAX_FSM_RELATIONS</varname>. The default is 20000.
This option can only be set at server start.
</para>
</listitem>
@ -1008,14 +1012,14 @@ SET ENABLE_SEQSCAN TO OFF;
<listitem>
<para>
This variable specifies one or more shared libraries that are
to be preloaded at server start. A parameterless initialization
function can optionally be called for each library. To specify
that, add a colon and the name of the initialization function after
the library name. For example
to be preloaded at server start. A parameterless
initialization function can optionally be called for each
library. To specify that, add a colon and the name of the
initialization function after the library name. For example
<literal>'$libdir/mylib:mylib_init'</literal> would cause
<literal>mylib</> to be preloaded and <literal>mylib_init</>
to be executed. If more than one library is to be loaded, separate
their names with commas.
to be executed. If more than one library is to be loaded,
separate their names with commas.
</para>
<para>
@ -1024,11 +1028,11 @@ SET ENABLE_SEQSCAN TO OFF;
</para>
<para>
PostgreSQL procedural language libraries may be preloaded in this way,
typically by using the syntax
<literal>'$libdir/plXXX:plXXX_init'</literal>
where <literal>XXX</literal> is <literal>pgsql</>,
<literal>perl</>, <literal>tcl</>, or <literal>python</>.
PostgreSQL procedural language libraries may be preloaded in
this way, typically by using the syntax
<literal>'$libdir/plXXX:plXXX_init'</literal> where
<literal>XXX</literal> is <literal>pgsql</>, <literal>perl</>,
<literal>tcl</>, or <literal>python</>.
</para>
<para>
@ -1075,27 +1079,29 @@ SET ENABLE_SEQSCAN TO OFF;
</para>
<para>
However, this operation does slow down
<productname>PostgreSQL</> because at transaction commit it has
wait for the operating system to flush the write-ahead log.
Without <function>fsync</>, the operating system is allowed to
do its best in buffering, sorting, and delaying writes, which
can considerably increase performance. However, if the system
crashes, the results of the last few committed transactions may
be lost in part or whole. In the worst case, unrecoverable data
corruption may occur.
However, using <function>fsync()</function> results in a
performance penalty: when a transaction is committed,
<productname>PostgreSQL</productname> must wait for the
operating system to flush the write-ahead log to disk. When
<varname>FSYNC</varname> is disabled, the operating system is
allowed to do its best in buffering, ordering, and delaying
writes. This can result in significantly improved performance.
However, if the system crashes, the results of the last few
committed transactions may be lost in part or whole. In the
worst case, unrecoverable data corruption may occur.
</para>
<para>
For the above reasons, everyone can decide for himself what to
do with the <varname>fsync</> option. Some administrators
always leave it off, some turn it off only for bulk loads,
where there is a clear restart point if something goes wrong,
and some leave it on just to be on the safe side. The default
is on so that you are on the safe side. If you trust your
operating system, your hardware, and your utility company (or
better your battery backup), you can consider disabling
<varname>fsync</varname>.
Due to the risks involved, there is no universally correct
setting for <varname>FSYNC</varname>. Some administrators
always disable <varname>FSYNC</varname>, while others only
turn it off for bulk loads, where there is a clear restart
point if something goes wrong, whereas some administrators
always leave <varname>FSYNC</varname> enabled. The default is
to enable <varname>FSYNC</varname>, for maximum reliability.
If you trust your operating system, your hardware, and your
utility company (or your battery backup), you can consider
disabling <varname>FSYNC</varname>.
</para>
<para>
@ -1143,10 +1149,10 @@ SET ENABLE_SEQSCAN TO OFF;
<term><varname>CHECKPOINT_SEGMENTS</varname> (<type>integer</type>)</term>
<listitem>
<para>
Maximum distance between automatic WAL checkpoints, in log file
segments (each segment is normally 16 megabytes).
This option can only be set at server start or in the
<filename>postgresql.conf</filename> file.
Maximum distance between automatic WAL checkpoints, in log
file segments (each segment is normally 16 megabytes). The
default is three. This option can only be set at server start
or in the <filename>postgresql.conf</filename> file.
</para>
</listitem>
</varlistentry>
@ -1155,9 +1161,10 @@ SET ENABLE_SEQSCAN TO OFF;
<term><varname>CHECKPOINT_TIMEOUT</varname> (<type>integer</type>)</term>
<listitem>
<para>
Maximum time between automatic WAL checkpoints, in seconds.
This option can only be set at server start or in the
<filename>postgresql.conf</filename> file.
Maximum time between automatic WAL checkpoints, in
seconds. The default is 300 seconds. This option can only be
set at server start or in the <filename>postgresql.conf</>
file.
</para>
</listitem>
</varlistentry>
@ -1166,9 +1173,10 @@ SET ENABLE_SEQSCAN TO OFF;
<term><varname>CHECKPOINT_WARNING</varname> (<type>integer</type>)</term>
<listitem>
<para>
Send a message to the server logs if checkpoints caused by the
filling of checkpoint segment files happens more frequently than
this number of seconds. Zero turns off the warning.
Write a message to the server logs if checkpoints caused by
the filling of checkpoint segment files happens more
frequently than this number of seconds. The default is 30
seconds. Zero turns off the warning.
</para>
</listitem>
</varlistentry>
@ -1178,16 +1186,17 @@ SET ENABLE_SEQSCAN TO OFF;
<term><varname>COMMIT_DELAY</varname> (<type>integer</type>)</term>
<listitem>
<para>
Time delay between writing a commit record to the WAL buffer and
flushing the buffer out to disk, in microseconds. A nonzero
delay allows multiple transactions to be committed with only one
<function>fsync</function> system call, if system load is high
enough additional transactions may become ready to commit within
the given interval. But the delay is just wasted if no other
transactions become ready to commit. Therefore, the delay is
only performed if at least <varname>COMMIT_SIBLINGS</varname> other transactions
are active at the instant that a server process has written its commit
record.
Time delay between writing a commit record to the WAL buffer
and flushing the buffer out to disk, in microseconds. A
nonzero delay allows multiple transactions to be committed
with only one <function>fsync()</function> system call, if
system load is high enough additional transactions may become
ready to commit within the given interval. But the delay is
just wasted if no other transactions become ready to
commit. Therefore, the delay is only performed if at least
<varname>COMMIT_SIBLINGS</varname> other transactions are
active at the instant that a server process has written its
commit record. The default is zero (no delay).
</para>
</listitem>
</varlistentry>
@ -1196,10 +1205,11 @@ SET ENABLE_SEQSCAN TO OFF;
<term><varname>COMMIT_SIBLINGS</varname> (<type>integer</type>)</term>
<listitem>
<para>
Minimum number of concurrent open transactions to require before
performing the <varname>COMMIT_DELAY</> delay. A larger value
makes it more probable that at least one other transaction will
become ready to commit during the delay interval.
Minimum number of concurrent open transactions to require
before performing the <varname>COMMIT_DELAY</> delay. A larger
value makes it more probable that at least one other
transaction will become ready to commit during the delay
interval. The default is five.
</para>
</listitem>
</varlistentry>
@ -1209,20 +1219,36 @@ SET ENABLE_SEQSCAN TO OFF;
</sect2>
<sect2 id="runtime-config-query">
<title>Query Tuning</title>
<title>Query Planning</title>
<sect3 id="runtime-config-query-enable">
<title>Planner Method Enabling</title>
<title>Planner Method Configuration</title>
<note>
<para>
These configuration parameters provide a crude method for
influencing the query plans chosen by the query optimizer. If
the default plan chosen by the optimizer is not optimal, a
temporary solution may be found by using one of these
configuration parameters to force the optimizer to choose a
better plan. Other ways to improve the quality of the plans
chosen by the optimizer include configuring the <xref
linkend="runtime-config-query-constants"
endterm="runtime-config-query-constants-title">, running
<command>ANALYZE</command> more frequently, and increasing the
amount of statistics collected for a particular column using
<command>ALTER TABLE SET STATISTICS</command>.
</para>
</note>
<variablelist>
<varlistentry>
<term><varname>ENABLE_HASHAGG</varname> (<type>boolean</type>)</term>
<listitem>
<para>
Enables or disables the query planner's use of hashed aggregation
plan types. The default is on. This is used for debugging the query
planner.
Enables or disables the query planner's use of hashed
aggregation plan types. The default is on. This is used for
debugging the query planner.
</para>
</listitem>
</varlistentry>
@ -1232,8 +1258,8 @@ SET ENABLE_SEQSCAN TO OFF;
<listitem>
<para>
Enables or disables the query planner's use of hash-join plan
types. The default is on. This is used for debugging the
query planner.
types. The default is on. This is used for debugging the query
planner.
</para>
</listitem>
</varlistentry>
@ -1247,8 +1273,8 @@ SET ENABLE_SEQSCAN TO OFF;
<listitem>
<para>
Enables or disables the query planner's use of index-scan plan
types. The default is on. This is used to debugging the
query planner.
types. The default is on. This is used for debugging the query
planner.
</para>
</listitem>
</varlistentry>
@ -1258,8 +1284,8 @@ SET ENABLE_SEQSCAN TO OFF;
<listitem>
<para>
Enables or disables the query planner's use of merge-join plan
types. The default is on. This is used for debugging the
query planner.
types. The default is on. This is used for debugging the query
planner.
</para>
</listitem>
</varlistentry>
@ -1311,9 +1337,9 @@ SET ENABLE_SEQSCAN TO OFF;
<term><varname>ENABLE_TIDSCAN</varname> (<type>boolean</type>)</term>
<listitem>
<para>
Enables or disables the query planner's use of <acronym>TID</> scan plan
types. The default is on. This is used for debugging the
query planner.
Enables or disables the query planner's use of <acronym>TID</>
scan plan types. The default is on. This is used for debugging
the query planner.
</para>
</listitem>
</varlistentry>
@ -1321,7 +1347,9 @@ SET ENABLE_SEQSCAN TO OFF;
</variablelist>
</sect3>
<sect3 id="runtime-config-query-constants">
<title>Planner Cost Constants</title>
<title id="runtime-config-query-constants-title">
Planner Cost Constants
</title>
<note>
<para>
@ -1339,10 +1367,10 @@ SET ENABLE_SEQSCAN TO OFF;
<listitem>
<para>
Sets the planner's assumption about the effective size of the
disk cache (that is, the portion of the kernel's disk cache that
will be used for <productname>PostgreSQL</productname> data
files). This is measured in disk pages, which are normally 8 kB
each.
disk cache (that is, the portion of the kernel's disk cache
that will be used for <productname>PostgreSQL</productname>
data files). This is measured in disk pages, which are
normally 8192 bytes each.
</para>
</listitem>
</varlistentry>
@ -2002,7 +2030,7 @@ SET ENABLE_SEQSCAN TO OFF;
</para>
<para>
The value for <varname>search_path</varname> has to be a comma-separated
The value for <varname>SEARCH_PATH</varname> has to be a comma-separated
list of schema names. If one of the list items is
the special value <literal>$user</literal>, then the schema
having the name returned by <function>SESSION_USER</> is substituted, if there
@ -2040,11 +2068,11 @@ SET ENABLE_SEQSCAN TO OFF;
<para>
The current effective value of the search path can be examined
via the SQL function <function>current_schemas()</>. This is not
quite the same as examining the value of
<varname>search_path</varname>, since <function>current_schemas()</>
shows how the requests appearing in <varname>search_path</varname>
were resolved.
via the <acronym>SQL</acronym> function
<function>current_schemas()</>. This is not quite the same as
examining the value of <varname>SEARCH_PATH</varname>, since
<function>current_schemas()</> shows how the requests
appearing in <varname>SEARCH_PATH</varname> were resolved.
</para>
<para>
@ -2381,8 +2409,8 @@ dynamic_library_path = '/usr/local/lib/postgresql:/home/my_project/lib:$libdir'
<listitem>
<para>
The shared lock table is sized on the assumption that at most
<varname>max_locks_per_transaction</> *
<varname>max_connections</varname> distinct objects will need to
<varname>MAX_LOCKS_PER_TRANSACTION</> *
<varname>MAX_CONNECTIONS</varname> distinct objects will need to
be locked at any one time. The default, 64, has historically
proven sufficient, but you might need to raise this value if you
have clients that touch many different tables in a single
@ -2590,7 +2618,7 @@ dynamic_library_path = '/usr/local/lib/postgresql:/home/my_project/lib:$libdir'
<para>
Detection of a damaged page header normally causes
<productname>PostgreSQL</> to report an error, aborting the current
transaction. Setting <varname>zero_damaged_pages</> to true causes
transaction. Setting <varname>ZERO_DAMAGED_PAGES</> to true causes
the system to instead report a warning, zero out the damaged page,
and continue processing. This behavior <emphasis>will destroy data</>,
namely all the rows on the damaged page. But it allows you to get
@ -2786,7 +2814,7 @@ $ <userinput>postmaster -o '-S 1024 -s'</userinput>
<row>
<entry><varname>SHMMAX</></>
<entry>Maximum size of shared memory segment (bytes)</>
<entry>250 kB + 8.2 kB * <varname>shared_buffers</> + 14.2 kB * <varname>max_connections</> up to infinity</entry>
<entry>250 kB + 8.2 kB * <varname>SHARED_BUFFERS</> + 14.2 kB * <varname>MAX_CONNECTIONS</> up to infinity</entry>
</row>
<row>
@ -3331,7 +3359,7 @@ default:\
processes do so then the system-wide limit can easily be exceeded.
If you find this happening, and you do not want to alter the system-wide
limit, you can set <productname>PostgreSQL</productname>'s
<varname>max_files_per_process</varname> configuration parameter to
<varname>MAX_FILES_PER_PROCESS</varname> configuration parameter to
limit the consumption of open files.
</para>
</sect2>
@ -3440,7 +3468,7 @@ $ <userinput>kill -INT `head -1 /usr/local/pgsql/data/postmaster.pid`</userinput
With <acronym>SSL</> support compiled in, the
<productname>PostgreSQL</> server can be started with
<acronym>SSL</> enabled by setting the parameter
<varname>ssl</varname> to on in <filename>postgresql.conf</>. When
<varname>SSL</varname> to on in <filename>postgresql.conf</>. When
starting in <acronym>SSL</> mode, the server will look for the
files <filename>server.key</> and <filename>server.crt</> in the
data directory, which should contain the server private key