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Implement partition-wise grouping/aggregation.

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If the partition keys of input relation are part of the GROUP BY
clause, all the rows belonging to a given group come from a single
partition.  This allows aggregation/grouping over a partitioned
relation to be broken down * into aggregation/grouping on each
partition.  This should be no worse, and often better, than the normal
approach.

If the GROUP BY clause does not contain all the partition keys, we can
still perform partial aggregation for each partition and then finalize
aggregation after appending the partial results.  This is less certain
to be a win, but it's still useful.

Jeevan Chalke, Ashutosh Bapat, Robert Haas.  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, and Rafia Sabih.

Discussion: http://postgr.es/m/CAM2+6=V64_xhstVHie0Rz=KPEQnLJMZt_e314P0jaT_oJ9MR8A@mail.gmail.com
This commit is contained in:
Robert Haas
2018-03-22 12:49:48 -04:00
parent 2058d6a22b
commit e2f1eb0ee3
17 changed files with 2552 additions and 214 deletions
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75
src/include/nodes/relation.h
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@@ -553,6 +553,7 @@ typedef enum RelOptKind
RELOPT_OTHER_MEMBER_REL,
RELOPT_OTHER_JOINREL,
RELOPT_UPPER_REL,
RELOPT_OTHER_UPPER_REL,
RELOPT_DEADREL
} RelOptKind;
@@ -570,12 +571,15 @@ typedef enum RelOptKind
(rel)->reloptkind == RELOPT_OTHER_JOINREL)
/* Is the given relation an upper relation? */
#define IS_UPPER_REL(rel) ((rel)->reloptkind == RELOPT_UPPER_REL)
#define IS_UPPER_REL(rel) \
((rel)->reloptkind == RELOPT_UPPER_REL || \
(rel)->reloptkind == RELOPT_OTHER_UPPER_REL)
/* Is the given relation an "other" relation? */
#define IS_OTHER_REL(rel) \
((rel)->reloptkind == RELOPT_OTHER_MEMBER_REL || \
(rel)->reloptkind == RELOPT_OTHER_JOINREL)
(rel)->reloptkind == RELOPT_OTHER_JOINREL || \
(rel)->reloptkind == RELOPT_OTHER_UPPER_REL)
typedef struct RelOptInfo
{
@@ -2291,6 +2295,73 @@ typedef struct JoinPathExtraData
Relids param_source_rels;
} JoinPathExtraData;
/*
* Various flags indicating what kinds of grouping are possible.
*
* GROUPING_CAN_USE_SORT should be set if it's possible to perform
* sort-based implementations of grouping. When grouping sets are in use,
* this will be true if sorting is potentially usable for any of the grouping
* sets, even if it's not usable for all of them.
*
* GROUPING_CAN_USE_HASH should be set if it's possible to perform
* hash-based implementations of grouping.
*
* GROUPING_CAN_PARTIAL_AGG should be set if the aggregation is of a type
* for which we support partial aggregation (not, for example, grouping sets).
* It says nothing about parallel-safety or the availability of suitable paths.
*/
#define GROUPING_CAN_USE_SORT 0x0001
#define GROUPING_CAN_USE_HASH 0x0002
#define GROUPING_CAN_PARTIAL_AGG 0x0004
/*
* What kind of partitionwise aggregation is in use?
*
* PARTITIONWISE_AGGREGATE_NONE: Not used.
*
* PARTITIONWISE_AGGREGATE_FULL: Aggregate each partition separately, and
* append the results.
*
* PARTITIONWISE_AGGREGATE_PARTIAL: Partially aggregate each partition
* separately, append the results, and then finalize aggregation.
*/
typedef enum
{
PARTITIONWISE_AGGREGATE_NONE,
PARTITIONWISE_AGGREGATE_FULL,
PARTITIONWISE_AGGREGATE_PARTIAL
} PartitionwiseAggregateType;
/*
* Struct for extra information passed to subroutines of create_grouping_paths
*
* flags indicating what kinds of grouping are possible.
* partial_costs_set is true if the agg_partial_costs and agg_final_costs
* have been initialized.
* agg_partial_costs gives partial aggregation costs.
* agg_final_costs gives finalization costs.
* target is the PathTarget to be used while creating paths.
* target_parallel_safe is true if target is parallel safe.
* havingQual gives list of quals to be applied after aggregation.
* targetList gives list of columns to be projected.
* patype is the type of partitionwise aggregation that is being performed.
*/
typedef struct
{
/* Data which remains constant once set. */
int flags;
bool partial_costs_set;
AggClauseCosts agg_partial_costs;
AggClauseCosts agg_final_costs;
/* Data which may differ across partitions. */
PathTarget *target;
bool target_parallel_safe;
Node *havingQual;
List *targetList;
PartitionwiseAggregateType patype;
} GroupPathExtraData;
/*
* For speed reasons, cost estimation for join paths is performed in two
* phases: the first phase tries to quickly derive a lower bound for the