diff options
Diffstat (limited to 'src/backend/optimizer/path/allpaths.c')
| -rw-r--r-- | src/backend/optimizer/path/allpaths.c | 64 |
1 files changed, 44 insertions, 20 deletions
diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c index cc77ff9e1f0..17c1edd9703 100644 --- a/src/backend/optimizer/path/allpaths.c +++ b/src/backend/optimizer/path/allpaths.c @@ -659,31 +659,55 @@ set_plain_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte) static void create_parallel_paths(PlannerInfo *root, RelOptInfo *rel) { - int parallel_threshold = 1000; - int parallel_degree = 1; + int parallel_degree = 1; /* - * If this relation is too small to be worth a parallel scan, just return - * without doing anything ... unless it's an inheritance child. In that case, - * we want to generate a parallel path here anyway. It might not be worthwhile - * just for this relation, but when combined with all of its inheritance siblings - * it may well pay off. + * If the user has set the parallel_degree reloption, we decide what to do + * based on the value of that option. Otherwise, we estimate a value. */ - if (rel->pages < parallel_threshold && rel->reloptkind == RELOPT_BASEREL) - return; + if (rel->rel_parallel_degree != -1) + { + /* + * If parallel_degree = 0 is set for this relation, bail out. The + * user does not want a parallel path for this relation. + */ + if (rel->rel_parallel_degree == 0) + return; - /* - * Limit the degree of parallelism logarithmically based on the size of the - * relation. This probably needs to be a good deal more sophisticated, but we - * need something here for now. - */ - while (rel->pages > parallel_threshold * 3 && - parallel_degree < max_parallel_degree) + /* + * Use the table parallel_degree, but don't go further than + * max_parallel_degree. + */ + parallel_degree = Min(rel->rel_parallel_degree, max_parallel_degree); + } + else { - parallel_degree++; - parallel_threshold *= 3; - if (parallel_threshold >= PG_INT32_MAX / 3) - break; + int parallel_threshold = 1000; + + /* + * If this relation is too small to be worth a parallel scan, just + * return without doing anything ... unless it's an inheritance child. + * In that case, we want to generate a parallel path here anyway. It + * might not be worthwhile just for this relation, but when combined + * with all of its inheritance siblings it may well pay off. + */ + if (rel->pages < parallel_threshold && + rel->reloptkind == RELOPT_BASEREL) + return; + + /* + * Limit the degree of parallelism logarithmically based on the size + * of the relation. This probably needs to be a good deal more + * sophisticated, but we need something here for now. + */ + while (rel->pages > parallel_threshold * 3 && + parallel_degree < max_parallel_degree) + { + parallel_degree++; + parallel_threshold *= 3; + if (parallel_threshold >= PG_INT32_MAX / 3) + break; + } } /* Add an unordered partial path based on a parallel sequential scan. */ |