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| -rw-r--r-- | doc/src/sgml/runtime.sgml | 83 |
1 files changed, 82 insertions, 1 deletions
diff --git a/doc/src/sgml/runtime.sgml b/doc/src/sgml/runtime.sgml index 71d7f0621c8..67e8931273a 100644 --- a/doc/src/sgml/runtime.sgml +++ b/doc/src/sgml/runtime.sgml @@ -1,5 +1,5 @@ <!-- -$PostgreSQL: pgsql/doc/src/sgml/runtime.sgml,v 1.236 2004/02/03 17:34:02 tgl Exp $ +$PostgreSQL: pgsql/doc/src/sgml/runtime.sgml,v 1.237 2004/02/13 12:25:09 wieck Exp $ --> <Chapter Id="runtime"> @@ -990,6 +990,87 @@ SET ENABLE_SEQSCAN TO OFF; </variablelist> </sect3> + + <sect3 id="runtime-config-resource-vacuum-cost"> + <title>Cost Based Vacuum Delay</title> + + <variablelist> + <varlistentry> + <term><varname>vacuum_cost_page_hit</varname> (<type>integer</type>)</term> + <listitem> + <para> + During a default <command>VACUUM</command> (not + <command>FULL</command>) the system maintains and internal counter + accumulating the cost of various operations performed. When the + accumulated cost reaches a limit, the backend performing the + <command>VACUUM</command> will sleep for a while, reset the + accumulator and continue. The intention is to lower the IO impact + of <command>VACUUM</command>. + </para> + + <para> + The variable <varname>vacuum_cost_page_hit</varname> is the cost + for vacuuming a buffer found inside the shared buffer cache. + It represents the cost to lock the buffer pool, lookup the + shared hash table and to actually scan the block content. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>vacuum_cost_page_miss</varname> (<type>integer</type>)</term> + <listitem> + <para> + The cost for vacuuming a buffer that has to be read from disk. + This represents the effort to lock the buffer pool, lookup the + cache directory, reading the block from disk and scanning the + content. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>vacuum_cost_page_dirty</varname> (<type>integer</type>)</term> + <listitem> + <para> + This extra cost is added when vacuum modifies a block that was + clean before. It represents the extra IO required to flush the + dirty block out to disk again. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>vacuum_cost_limit</varname> (<type>integer</type>)</term> + <listitem> + <para> + This is the cost limit that must be reached or exceeded before + the <command>VACUUM</command> will nap. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>vacuum_cost_naptime</varname> (<type>integer</type>)</term> + <listitem> + <para> + The time im milliseconds the <command>VACUUM</command> will + nap when the cost limit has been reached or exceeded. + There are certain bulk operations that hold critical + locks and should therefore perform + as quickly as possible. Because of that it is possible that the + cost actually accumulates far higher than this limit. To compensate + for this, the final naptime is calculated as + <varname>vacuum_cost_naptime</varname> * + <varname>accumulated_balance</varname> / + <varname>vacuum_cost_limit</varname> with a maximum of + <varname>vacuum_cost_naptime</varname> * 4. + </para> + </listitem> + </varlistentry> + + </variablelist> + </sect3> </sect2> <sect2 id="runtime-config-wal"> |