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Replace min_parallel_relation_size with two new GUCs.

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When min_parallel_relation_size was added, the only supported type
of parallel scan was a parallel sequential scan, but there are
pending patches for parallel index scan, parallel index-only scan,
and parallel bitmap heap scan.  Those patches introduce two new
types of complications: first, what's relevant is not really the
total size of the relation but the portion of it that we will scan;
and second, index pages and heap pages shouldn't necessarily be
treated in exactly the same way.  Typically, the number of index
pages will be quite small, but that doesn't necessarily mean that
a parallel index scan can't pay off.

Therefore, we introduce min_parallel_table_scan_size, which works
out a degree of parallelism for scans based on the number of table
pages that will be scanned (and which is therefore equivalent to
min_parallel_relation_size for parallel sequential scans) and also
min_parallel_index_scan_size which can be used to work out a degree
of parallelism based on the number of index pages that will be
scanned.

Amit Kapila and Robert Haas

Discussion: http://postgr.es/m/CAA4eK1KowGSYYVpd2qPpaPPA5R90r++QwDFbrRECTE9H_HvpOg@mail.gmail.com
Discussion: http://postgr.es/m/CAA4eK1+TnM4pXQbvn7OXqam+k_HZqb0ROZUMxOiL6DWJYCyYow@mail.gmail.com
This commit is contained in:
Robert Haas
2017-02-15 13:37:24 -05:00
parent 5d40286985
commit 51ee6f3160
8 changed files with 105 additions and 38 deletions
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19
src/backend/utils/misc/guc.c
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@ -2776,16 +2776,27 @@ static struct config_int ConfigureNamesInt[] =
},
{
{"min_parallel_relation_size", PGC_USERSET, QUERY_TUNING_COST,
gettext_noop("Sets the minimum size of relations to be considered for parallel scan."),
NULL,
{"min_parallel_table_scan_size", PGC_USERSET, QUERY_TUNING_COST,
gettext_noop("Sets the minimum amount of table data for a parallel scan."),
gettext_noop("If the planner estimates that it will read a number of table pages too small to reach this limit, a parallel scan will not be considered."),
GUC_UNIT_BLOCKS,
},
&min_parallel_relation_size,
&min_parallel_table_scan_size,
(8 * 1024 * 1024) / BLCKSZ, 0, INT_MAX / 3,
NULL, NULL, NULL
},
{
{"min_parallel_index_scan_size", PGC_USERSET, QUERY_TUNING_COST,
gettext_noop("Sets the minimum amount of index data for a parallel scan."),
gettext_noop("If the planner estimates that it will read a number of index pages too small to reach this limit, a parallel scan will not be considered."),
GUC_UNIT_BLOCKS,
},
&min_parallel_index_scan_size,
(512 * 1024) / BLCKSZ, 0, INT_MAX / 3,
NULL, NULL, NULL
},
{
/* Can't be set in postgresql.conf */
{"server_version_num", PGC_INTERNAL, PRESET_OPTIONS,