diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index dc63d7d5e40..95afc2c483d 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -3835,16 +3835,37 @@ ANY num_sync (
- min_parallel_relation_size (integer)
+
+ min_parallel_table_scan_size (integer)
- min_parallel_relation_size configuration parameter
+ min_parallel_table_scan_size configuration parameter
- Sets the minimum size of relations to be considered for parallel scan.
- The default is 8 megabytes (8MB).
+ Sets the minimum amount of table data that must be scanned in order
+ for a parallel scan to be considered. For a parallel sequential scan,
+ the amount of table data scanned is always equal to the size of the
+ table, but when indexes are used the amount of table data
+ scanned will normally be less. The default is 8
+ megabytes (8MB).
+
+
+
+
+
+ min_parallel_index_scan_size (integer)
+
+ min_parallel_index_scan_size configuration parameter
+
+
+
+
+ Sets the minimum amount of index data that must be scanned in order
+ for a parallel scan to be considered. Note that a parallel index scan
+ typically won't touch the entire index; it is the number of pages
+ which the planner believes will actually be touched by the scan which
+ is relevant. The default is 512 kilobytes (512kB).
diff --git a/doc/src/sgml/release-9.6.sgml b/doc/src/sgml/release-9.6.sgml
index bffcaac46e7..02cc8c9003c 100644
--- a/doc/src/sgml/release-9.6.sgml
+++ b/doc/src/sgml/release-9.6.sgml
@@ -2407,8 +2407,8 @@ and many others in the same vein
is available through other new configuration parameters
,
, , and .
+ linkend="guc-parallel-tuple-cost">, and
+ min_parallel_relation_size.
diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index 5c189874efa..85505c57d36 100644
--- a/src/backend/optimizer/path/allpaths.c
+++ b/src/backend/optimizer/path/allpaths.c
@@ -57,7 +57,8 @@ typedef struct pushdown_safety_info
/* These parameters are set by GUC */
bool enable_geqo = false; /* just in case GUC doesn't set it */
int geqo_threshold;
-int min_parallel_relation_size;
+int min_parallel_table_scan_size;
+int min_parallel_index_scan_size;
/* Hook for plugins to get control in set_rel_pathlist() */
set_rel_pathlist_hook_type set_rel_pathlist_hook = NULL;
@@ -126,7 +127,8 @@ static void subquery_push_qual(Query *subquery,
static void recurse_push_qual(Node *setOp, Query *topquery,
RangeTblEntry *rte, Index rti, Node *qual);
static void remove_unused_subquery_outputs(Query *subquery, RelOptInfo *rel);
-static int compute_parallel_worker(RelOptInfo *rel, BlockNumber pages);
+static int compute_parallel_worker(RelOptInfo *rel, BlockNumber heap_pages,
+ BlockNumber index_pages);
/*
@@ -679,7 +681,7 @@ create_plain_partial_paths(PlannerInfo *root, RelOptInfo *rel)
{
int parallel_workers;
- parallel_workers = compute_parallel_worker(rel, rel->pages);
+ parallel_workers = compute_parallel_worker(rel, rel->pages, 0);
/* If any limit was set to zero, the user doesn't want a parallel scan. */
if (parallel_workers <= 0)
@@ -2876,13 +2878,20 @@ remove_unused_subquery_outputs(Query *subquery, RelOptInfo *rel)
/*
* Compute the number of parallel workers that should be used to scan a
- * relation. "pages" is the number of pages from the relation that we
- * expect to scan.
+ * relation. We compute the parallel workers based on the size of the heap to
+ * be scanned and the size of the index to be scanned, then choose a minimum
+ * of those.
+ *
+ * "heap_pages" is the number of pages from the table that we expect to scan.
+ * "index_pages" is the number of pages from the index that we expect to scan.
*/
static int
-compute_parallel_worker(RelOptInfo *rel, BlockNumber pages)
+compute_parallel_worker(RelOptInfo *rel, BlockNumber heap_pages,
+ BlockNumber index_pages)
{
- int parallel_workers;
+ int parallel_workers = 0;
+ int heap_parallel_workers = 1;
+ int index_parallel_workers = 1;
/*
* If the user has set the parallel_workers reloption, use that; otherwise
@@ -2892,7 +2901,8 @@ compute_parallel_worker(RelOptInfo *rel, BlockNumber pages)
parallel_workers = rel->rel_parallel_workers;
else
{
- int parallel_threshold;
+ int heap_parallel_threshold;
+ int index_parallel_threshold;
/*
* If this relation is too small to be worth a parallel scan, just
@@ -2901,25 +2911,48 @@ compute_parallel_worker(RelOptInfo *rel, BlockNumber pages)
* might not be worthwhile just for this relation, but when combined
* with all of its inheritance siblings it may well pay off.
*/
- if (pages < (BlockNumber) min_parallel_relation_size &&
+ if (heap_pages < (BlockNumber) min_parallel_table_scan_size &&
+ index_pages < (BlockNumber) min_parallel_index_scan_size &&
rel->reloptkind == RELOPT_BASEREL)
return 0;
- /*
- * Select the number of workers based on the log of the size of the
- * relation. This probably needs to be a good deal more
- * sophisticated, but we need something here for now. Note that the
- * upper limit of the min_parallel_relation_size GUC is chosen to
- * prevent overflow here.
- */
- parallel_workers = 1;
- parallel_threshold = Max(min_parallel_relation_size, 1);
- while (pages >= (BlockNumber) (parallel_threshold * 3))
+ if (heap_pages > 0)
{
- parallel_workers++;
- parallel_threshold *= 3;
- if (parallel_threshold > INT_MAX / 3)
- break; /* avoid overflow */
+ /*
+ * Select the number of workers based on the log of the size of
+ * the relation. This probably needs to be a good deal more
+ * sophisticated, but we need something here for now. Note that
+ * the upper limit of the min_parallel_table_scan_size GUC is
+ * chosen to prevent overflow here.
+ */
+ heap_parallel_threshold = Max(min_parallel_table_scan_size, 1);
+ while (heap_pages >= (BlockNumber) (heap_parallel_threshold * 3))
+ {
+ heap_parallel_workers++;
+ heap_parallel_threshold *= 3;
+ if (heap_parallel_threshold > INT_MAX / 3)
+ break; /* avoid overflow */
+ }
+
+ parallel_workers = heap_parallel_workers;
+ }
+
+ if (index_pages > 0)
+ {
+ /* same calculation as for heap_pages above */
+ index_parallel_threshold = Max(min_parallel_index_scan_size, 1);
+ while (index_pages >= (BlockNumber) (index_parallel_threshold * 3))
+ {
+ index_parallel_workers++;
+ index_parallel_threshold *= 3;
+ if (index_parallel_threshold > INT_MAX / 3)
+ break; /* avoid overflow */
+ }
+
+ if (parallel_workers > 0)
+ parallel_workers = Min(parallel_workers, index_parallel_workers);
+ else
+ parallel_workers = index_parallel_workers;
}
}
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 0249721204a..5d8fb2edb8f 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -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,
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 661b0fa9b6e..157d775853a 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -300,7 +300,8 @@
#cpu_operator_cost = 0.0025 # same scale as above
#parallel_tuple_cost = 0.1 # same scale as above
#parallel_setup_cost = 1000.0 # same scale as above
-#min_parallel_relation_size = 8MB
+#min_parallel_table_scan_size = 8MB
+#min_parallel_index_scan_size = 512kB
#effective_cache_size = 4GB
# - Genetic Query Optimizer -
diff --git a/src/include/optimizer/paths.h b/src/include/optimizer/paths.h
index 81a9be7c674..81e7a4274da 100644
--- a/src/include/optimizer/paths.h
+++ b/src/include/optimizer/paths.h
@@ -22,7 +22,8 @@
*/
extern bool enable_geqo;
extern int geqo_threshold;
-extern int min_parallel_relation_size;
+extern int min_parallel_table_scan_size;
+extern int min_parallel_index_scan_size;
/* Hook for plugins to get control in set_rel_pathlist() */
typedef void (*set_rel_pathlist_hook_type) (PlannerInfo *root,
diff --git a/src/test/regress/expected/select_parallel.out b/src/test/regress/expected/select_parallel.out
index 8786678f0cf..3692d4f1b81 100644
--- a/src/test/regress/expected/select_parallel.out
+++ b/src/test/regress/expected/select_parallel.out
@@ -9,7 +9,7 @@ begin isolation level repeatable read;
-- encourage use of parallel plans
set parallel_setup_cost=0;
set parallel_tuple_cost=0;
-set min_parallel_relation_size=0;
+set min_parallel_table_scan_size=0;
set max_parallel_workers_per_gather=4;
explain (costs off)
select count(*) from a_star;
diff --git a/src/test/regress/sql/select_parallel.sql b/src/test/regress/sql/select_parallel.sql
index def9939d2e6..f4f9dd5ab67 100644
--- a/src/test/regress/sql/select_parallel.sql
+++ b/src/test/regress/sql/select_parallel.sql
@@ -12,7 +12,7 @@ begin isolation level repeatable read;
-- encourage use of parallel plans
set parallel_setup_cost=0;
set parallel_tuple_cost=0;
-set min_parallel_relation_size=0;
+set min_parallel_table_scan_size=0;
set max_parallel_workers_per_gather=4;
explain (costs off)