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robertmhaasrobertmhaas
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Add a new upper planner relation for partially-aggregated results.
Up until now, we've abused grouped_rel->partial_pathlist as a place to store partial paths that have been partially aggregate, but that's really not correct, because a partial path for a relation is supposed to be one which produces the correct results with the addition of only a Gather or Gather Merge node, and these paths also require a Finalize Aggregate step. Instead, add a new partially_group_rel which can hold either partial paths (which need to be gathered and then have aggregation finalized) or non-partial paths (which only need to have aggregation finalized). This allows us to reuse generate_gather_paths for partially_grouped_rel instead of writing new code, so that this patch actually basically no net new code while making things cleaner, simplifying things for pending patches for partition-wise aggregate. Robert Haas and Jeevan Chalke. The larger patch series of which this patch is a part was also reviewed and tested by Antonin Houska, Rajkumar Raghuwanshi, David Rowley, Dilip Kumar, Konstantin Knizhnik, Pascal Legrand, Rafia Sabih, and me. Discussion: http://postgr.es/m/CA+TgmobrzFYS3+U8a_BCy3-hOvh5UyJbC18rEcYehxhpw5=ETA@mail.gmail.com Discussion: http://postgr.es/m/CA+TgmoZyQEjdBNuoG9-wC5GQ5GrO4544Myo13dVptvx+uLg9uQ@mail.gmail.com
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‎src/backend/optimizer/README

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Original file line numberDiff line numberDiff line change
@@ -998,6 +998,7 @@ considered useful for each step. Currently, we may create these types of
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additional RelOptInfos during upper-level planning:
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UPPERREL_SETOP result of UNION/INTERSECT/EXCEPT, if any
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UPPERREL_PARTIAL_GROUP_AGG result of partial grouping/aggregation, if any
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UPPERREL_GROUP_AGG result of grouping/aggregation, if any
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UPPERREL_WINDOW result of window functions, if any
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UPPERREL_DISTINCT result of "SELECT DISTINCT", if any

‎src/backend/optimizer/geqo/geqo_eval.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -268,7 +268,7 @@ merge_clump(PlannerInfo *root, List *clumps, Clump *new_clump, bool force)
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generate_partitionwise_join_paths(root, joinrel);
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/* Create GatherPaths for any useful partial paths for rel */
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generate_gather_paths(root, joinrel);
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generate_gather_paths(root, joinrel, false);
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/* Find and save the cheapest paths for this joinrel */
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set_cheapest(joinrel);

‎src/backend/optimizer/path/allpaths.c

Lines changed: 21 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -488,7 +488,7 @@ set_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
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* we'll consider gathering partial paths for the parent appendrel.)
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*/
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if (rel->reloptkind == RELOPT_BASEREL)
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generate_gather_paths(root, rel);
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generate_gather_paths(root, rel, false);
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/*
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* Allow a plugin to editorialize on the set of Paths for this base
@@ -2444,27 +2444,42 @@ set_worktable_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
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* This must not be called until after we're done creating all partial paths
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* for the specified relation. (Otherwise, add_partial_path might delete a
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* path that some GatherPath or GatherMergePath has a reference to.)
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*
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* If we're generating paths for a scan or join relation, override_rows will
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* be false, and we'll just use the relation's size estimate. When we're
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* being called for a partially-grouped path, though, we need to override
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* the rowcount estimate. (It's not clear that the particular value we're
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* using here is actually best, but the underlying rel has no estimate so
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* we must do something.)
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*/
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void
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generate_gather_paths(PlannerInfo *root, RelOptInfo *rel)
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generate_gather_paths(PlannerInfo *root, RelOptInfo *rel, bool override_rows)
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{
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Path *cheapest_partial_path;
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Path *simple_gather_path;
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ListCell *lc;
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double rows;
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double *rowsp = NULL;
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/* If there are no partial paths, there's nothing to do here. */
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if (rel->partial_pathlist == NIL)
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return;
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/* Should we override the rel's rowcount estimate? */
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if (override_rows)
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rowsp = &rows;
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/*
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* The output of Gather is always unsorted, so there's only one partial
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* path of interest: the cheapest one. That will be the one at the front
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* of partial_pathlist because of the way add_partial_path works.
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*/
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cheapest_partial_path = linitial(rel->partial_pathlist);
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rows =
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cheapest_partial_path->rows * cheapest_partial_path->parallel_workers;
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simple_gather_path = (Path *)
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create_gather_path(root, rel, cheapest_partial_path, rel->reltarget,
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NULL, NULL);
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NULL, rowsp);
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add_path(rel, simple_gather_path);
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/*
@@ -2479,8 +2494,9 @@ generate_gather_paths(PlannerInfo *root, RelOptInfo *rel)
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if (subpath->pathkeys == NIL)
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continue;
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rows = subpath->rows * subpath->parallel_workers;
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path = create_gather_merge_path(root, rel, subpath, rel->reltarget,
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subpath->pathkeys, NULL, NULL);
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subpath->pathkeys, NULL, rowsp);
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add_path(rel, &path->path);
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}
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}
@@ -2653,7 +2669,7 @@ standard_join_search(PlannerInfo *root, int levels_needed, List *initial_rels)
26532669
generate_partitionwise_join_paths(root, rel);
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/* Create GatherPaths for any useful partial paths for rel */
2656-
generate_gather_paths(root, rel);
2672+
generate_gather_paths(root, rel, false);
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/* Find and save the cheapest paths for this rel */
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set_cheapest(rel);

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