diff options
| -rw-r--r-- | doc/src/sgml/ref/vacuum.sgml | 32 |
1 files changed, 16 insertions, 16 deletions
diff --git a/doc/src/sgml/ref/vacuum.sgml b/doc/src/sgml/ref/vacuum.sgml index 26ede69bb31..21ab57d8804 100644 --- a/doc/src/sgml/ref/vacuum.sgml +++ b/doc/src/sgml/ref/vacuum.sgml @@ -235,22 +235,22 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet Perform index vacuum and index cleanup phases of <command>VACUUM</command> in parallel using <replaceable class="parameter">integer</replaceable> background workers (for the details of each vacuum phase, please - refer to <xref linkend="vacuum-phases"/>). In plain <command>VACUUM</command> - (without <literal>FULL</literal>), if the <literal>PARALLEL</literal> option - is omitted, then the number of workers is determined based on the number of - indexes on the relation that support parallel vacuum operation and is further - limited by <xref linkend="guc-max-parallel-maintenance-workers"/>. An index - can participate in parallel vacuum if and only if the size of the index is - more than <xref linkend="guc-min-parallel-index-scan-size"/>. Please note - that it is not guaranteed that the number of parallel workers specified in - <replaceable class="parameter">integer</replaceable> will be used during - execution. It is possible for a vacuum to run with fewer workers than - specified, or even with no workers at all. Only one worker can be used per - index. So parallel workers are launched only when there are at least - <literal>2</literal> indexes in the table. Workers for vacuum are launched - before the start of each phase and exit at the end of the phase. These - behaviors might change in a future release. This option can't be used with - the <literal>FULL</literal> option. + refer to <xref linkend="vacuum-phases"/>). The number of workers used + to perform the operation is equal to the number of indexes on the + relation that support parallel vacuum which is limited by the number of + workers specified with <literal>PARALLEL</literal> option if any which is + further limited by <xref linkend="guc-max-parallel-maintenance-workers"/>. + An index can participate in parallel vacuum if and only if the size of the + index is more than <xref linkend="guc-min-parallel-index-scan-size"/>. + Please note that it is not guaranteed that the number of parallel workers + specified in <replaceable class="parameter">integer</replaceable> will be + used during execution. It is possible for a vacuum to run with fewer + workers than specified, or even with no workers at all. Only one worker + can be used per index. So parallel workers are launched only when there + are at least <literal>2</literal> indexes in the table. Workers for + vacuum are launched before the start of each phase and exit at the end of + the phase. These behaviors might change in a future release. This + option can't be used with the <literal>FULL</literal> option. </para> </listitem> </varlistentry> |