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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
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17
src/include/lib/knapsack.h Normal file
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/*
* knapsack.h
*
* Copyright (c) 2017, PostgreSQL Global Development Group
*
* src/include/lib/knapsack.h
*/
#ifndef KNAPSACK_H
#define KNAPSACK_H
#include "postgres.h"
#include "nodes/bitmapset.h"
extern Bitmapset *DiscreteKnapsack(int max_weight, int num_items,
int *item_weights, double *item_values);
#endif /* KNAPSACK_H */