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Support hashed aggregation with grouping sets.

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This extends the Aggregate node with two new features: HashAggregate
can now run multiple hashtables concurrently, and a new strategy
MixedAggregate populates hashtables while doing sorted grouping.

The planner will now attempt to save as many sorts as possible when
planning grouping sets queries, while not exceeding work_mem for the
estimated combined sizes of all hashtables used.  No SQL-level changes
are required.  There should be no user-visible impact other than the
new EXPLAIN output and possible changes to result ordering when ORDER
BY was not used (which affected a few regression tests).  The
enable_hashagg option is respected.

Author: Andrew Gierth
Reviewers: Mark Dilger, Andres Freund
Discussion: https://postgr.es/m/87vatszyhj.fsf@news-spur.riddles.org.uk
This commit is contained in:
Andrew Gierth
2017-03-27 04:20:54 +01:00
parent f0a6046bcb
commit b5635948ab
22 changed files with 2552 additions and 602 deletions
Download Patch File Download Diff File Expand all files Collapse all files

25
src/backend/commands/explain.c
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@ -1015,6 +1015,10 @@ ExplainNode(PlanState *planstate, List *ancestors,
pname = "HashAggregate";
strategy = "Hashed";
break;
case AGG_MIXED:
pname = "MixedAggregate";
strategy = "Mixed";
break;
default:
pname = "Aggregate ???";
strategy = "???";
@ -1978,6 +1982,19 @@ show_grouping_set_keys(PlanState *planstate,
ListCell *lc;
List *gsets = aggnode->groupingSets;
AttrNumber *keycols = aggnode->grpColIdx;
const char *keyname;
const char *keysetname;
if (aggnode->aggstrategy == AGG_HASHED || aggnode->aggstrategy == AGG_MIXED)
{
keyname = "Hash Key";
keysetname = "Hash Keys";
}
else
{
keyname = "Group Key";
keysetname = "Group Keys";
}
ExplainOpenGroup("Grouping Set", NULL, true, es);
@ -1992,7 +2009,7 @@ show_grouping_set_keys(PlanState *planstate,
es->indent++;
}
ExplainOpenGroup("Group Keys", "Group Keys", false, es);
ExplainOpenGroup(keysetname, keysetname, false, es);
foreach(lc, gsets)
{
@ -2016,12 +2033,12 @@ show_grouping_set_keys(PlanState *planstate,
}
if (!result && es->format == EXPLAIN_FORMAT_TEXT)
ExplainPropertyText("Group Key", "()", es);
ExplainPropertyText(keyname, "()", es);
else
ExplainPropertyListNested("Group Key", result, es);
ExplainPropertyListNested(keyname, result, es);
}
ExplainCloseGroup("Group Keys", "Group Keys", false, es);
ExplainCloseGroup(keysetname, keysetname, false, es);
if (sortnode && es->format == EXPLAIN_FORMAT_TEXT)
es->indent--;