diff options
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/config.sgml | 87 | ||||
| -rw-r--r-- | doc/src/sgml/wal.sgml | 11 |
2 files changed, 98 insertions, 0 deletions
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index 2f726331ac..6c73fb439c 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -1843,6 +1843,35 @@ include_dir 'conf.d' </para> </listitem> </varlistentry> + + <varlistentry id="guc-bgwriter-flush-after" xreflabel="bgwriter_flush_after"> + <term><varname>bgwriter_flush_after</varname> (<type>int</type>) + <indexterm> + <primary><varname>bgwriter_flush_after</> configuration parameter</primary> + </indexterm> + </term> + <listitem> + <para> + Whenever more than <varname>bgwriter_flush_after</varname> bytes have + been written by the bgwriter, attempt to force the OS to issue these + writes to the underlying storage. Doing so will limit the amount of + dirty data in the kernel's page cache, reducing the likelihood of + stalls when an fsync is issued at the end of a checkpoint, or when + the OS writes data back in larger batches in the background. Often + that will result in greatly reduced transaction latency, but there + also are some cases, especially with workloads that are bigger than + <xref linkend="guc-shared-buffers">, but smaller than the OS's page + cache, where performance might degrade. This setting may have no + effect on some platforms. The valid range is between + <literal>0</literal>, which disables controlled writeback, and + <literal>2MB</literal>. The default is <literal>512Kb</> on Linux, + <literal>0</> elsewhere. (Non-default values of + <symbol>BLCKSZ</symbol> change the default and maximum.) + This parameter can only be set in the <filename>postgresql.conf</> + file or on the server command line. + </para> + </listitem> + </varlistentry> </variablelist> <para> @@ -1944,6 +1973,35 @@ include_dir 'conf.d' </para> </listitem> </varlistentry> + + <varlistentry id="guc-backend-flush-after" xreflabel="backend_flush_after"> + <term><varname>backend_flush_after</varname> (<type>int</type>) + <indexterm> + <primary><varname>backend_flush_after</> configuration parameter</primary> + </indexterm> + </term> + <listitem> + <para> + Whenever more than <varname>backend_flush_after</varname> bytes have + been written by a single backend, attempt to force the OS to issue + these writes to the underlying storage. Doing so will limit the + amount of dirty data in the kernel's page cache, reducing the + likelihood of stalls when an fsync is issued at the end of a + checkpoint, or when the OS writes data back in larger batches in the + background. Often that will result in greatly reduced transaction + latency, but there also are some cases, especially with workloads + that are bigger than <xref linkend="guc-shared-buffers">, but smaller + than the OS's page cache, where performance might degrade. This + setting may have no effect on some platforms. The valid range is + between <literal>0</literal>, which disables controlled writeback, + and <literal>2MB</literal>. The default is <literal>128Kb</> on + Linux, <literal>0</> elsewhere. (Non-default values of + <symbol>BLCKSZ</symbol> change the default and maximum.) + This parameter can only be set in the <filename>postgresql.conf</> + file or on the server command line. + </para> + </listitem> + </varlistentry> </variablelist> </sect2> </sect1> @@ -2475,6 +2533,35 @@ include_dir 'conf.d' </listitem> </varlistentry> + <varlistentry id="guc-checkpoint-flush-after" xreflabel="checkpoint_flush_after"> + <term><varname>checkpoint_flush_after</varname> (<type>int</type>) + <indexterm> + <primary><varname>checkpoint_flush_after</> configuration parameter</primary> + </indexterm> + </term> + <listitem> + <para> + Whenever more than <varname>checkpoint_flush_after</varname> bytes + have been written while performing a checkpoint, attempt to force the + OS to issue these writes to the underlying storage. Doing so will + limit the amount of dirty data in the kernel's page cache, reducing + the likelihood of stalls when an fsync is issued at the end of the + checkpoint, or when the OS writes data back in larger batches in the + background. Often that will result in greatly reduced transaction + latency, but there also are some cases, especially with workloads + that are bigger than <xref linkend="guc-shared-buffers">, but smaller + than the OS's page cache, where performance might degrade. This + setting may have no effect on some platforms. The valid range is + between <literal>0</literal>, which disables controlled writeback, + and <literal>2MB</literal>. The default is <literal>128Kb</> on + Linux, <literal>0</> elsewhere. (Non-default values of + <symbol>BLCKSZ</symbol> change the default and maximum.) + This parameter can only be set in the <filename>postgresql.conf</> + file or on the server command line. + </para> + </listitem> + </varlistentry> + <varlistentry id="guc-checkpoint-warning" xreflabel="checkpoint_warning"> <term><varname>checkpoint_warning</varname> (<type>integer</type>) <indexterm> diff --git a/doc/src/sgml/wal.sgml b/doc/src/sgml/wal.sgml index e3941c9391..503ea8a2a7 100644 --- a/doc/src/sgml/wal.sgml +++ b/doc/src/sgml/wal.sgml @@ -546,6 +546,17 @@ </para> <para> + On Linux and POSIX platforms <xref linkend="guc-checkpoint-flush-after"> + allows to force the OS that pages written by the checkpoint should be + flushed to disk after a configurable number of bytes. Otherwise, these + pages may be kept in the OS's page cache, inducing a stall when + <literal>fsync</> is issued at the end of a checkpoint. This setting will + often help to reduce transaction latency, but it also can an adverse effect + on performance; particularly for workloads that are bigger than + <xref linkend="guc-shared-buffers">, but smaller than the OS's page cache. + </para> + + <para> The number of WAL segment files in <filename>pg_xlog</> directory depends on <varname>min_wal_size</>, <varname>max_wal_size</> and the amount of WAL generated in previous checkpoint cycles. When old log |