diff options
Diffstat (limited to 'doc/src/sgml/config.sgml')
| -rw-r--r-- | doc/src/sgml/config.sgml | 20 |
1 files changed, 18 insertions, 2 deletions
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index 061697b54cb..4e8c982dd59 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -1603,7 +1603,7 @@ include_dir 'conf.d' </term> <listitem> <para> - Specifies the maximum amount of disk space that a session can use + Specifies the maximum amount of disk space that a process can use for temporary files, such as sort and hash temporary files, or the storage file for a held cursor. A transaction attempting to exceed this limit will be canceled. @@ -1613,7 +1613,7 @@ include_dir 'conf.d' </para> <para> This setting constrains the total space used at any instant by all - temporary files used by a given <productname>PostgreSQL</> session. + temporary files used by a given <productname>PostgreSQL</> process. It should be noted that disk space used for explicit temporary tables, as opposed to temporary files used behind-the-scenes in query execution, does <emphasis>not</emphasis> count against this limit. @@ -2011,6 +2011,22 @@ include_dir 'conf.d' be inefficient. The default value is 2. Setting this value to 0 disables parallel query execution. </para> + + <para> + Note that parallel queries may consume very substantially more + resources than non-parallel queries, because each worker process is + a completely separate process which has roughly the same impact on the + system as an additional user session. This should be taken into + account when choosing a value for this setting, as well as when + configuring other settings that control resource utilization, such + as <xref linkend="guc-work-mem">. Resource limits such as + <varname>work_mem</> are applied individually to each worker, + which means the total utilization may be much higher across all + processes than it would normally be for any single process. + For example, a parallel query using 4 workers may use up to 5 times + as much CPU time, memory, I/O bandwidth, and so forth as a query which + uses no workers at all. + </para> </listitem> </varlistentry> |