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Share transition state between different aggregates when possible.

If there are two different aggregates in the query with same inputs, andthe aggregates have the same initial condition and transition function,only calculate the state value once, and only call the final functionsseparately. For example, AVG(x) and SUM(x) aggregates have the sametransition function, which accumulates the sum and number of input tuples.For a query like "SELECT AVG(x), SUM(x) FROM x", we can thereforeaccumulate the state function only once, which gives a nice speedup.David Rowley, reviewed and edited by me.

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8 files changed

+1132

-457

lines changed

src
- backend
  - executor
  - parser
    - parse_agg.c
- include
  - nodes
    - execnodes.h
  - parser
    - parse_agg.h
- test/regress
  - expected
    - aggregates.out
  - sql
    - aggregates.sql

8 files changed

+1132

-457

lines changed

`‎src/backend/executor/execQual.c`

Lines changed: 1 addition & 21 deletions

Original file line number	Diff line number	Diff line change
`@@ -4487,35 +4487,15 @@ ExecInitExpr(Expr node, PlanState parent)`
`4487`	`4487`	`break;`
`4488`	`4488`	`caseT_Aggref:`
`4489`	`4489`	`{`
`4490`		`-Aggrefaggref= (Aggref)node;`
`4491`	`4490`	`AggrefExprState*astate=makeNode(AggrefExprState);`
`4492`	`4491`
`4493`	`4492`	`astate->xprstate.evalfunc= (ExprStateEvalFunc)ExecEvalAggref;`
`4494`	`4493`	`if (parent&&IsA(parent,AggState))`
`4495`	`4494`	`{`
`4496`	`4495`	`AggStateaggstate= (AggState)parent;`
`4497`		`-intnaggs;`
`4498`	`4496`
`4499`	`4497`	`aggstate->aggs=lcons(astate,aggstate->aggs);`
`4500`		`-naggs=++aggstate->numaggs;`
`4501`		`-`
`4502`		`-astate->aggdirectargs= (List)ExecInitExpr((Expr)aggref->aggdirectargs,`
`4503`		`-parent);`
`4504`		`-astate->args= (List)ExecInitExpr((Expr)aggref->args,`
`4505`		`-parent);`
`4506`		`-astate->aggfilter=ExecInitExpr(aggref->aggfilter,`
`4507`		`-parent);`
`4508`		`-`
`4509`		`-/*`
`4510`		`- * Complain if the aggregate's arguments contain any`
`4511`		`- * aggregates; nested agg functions are semantically`
`4512`		`- * nonsensical. (This should have been caught earlier,`
`4513`		`- * but we defend against it here anyway.)`
`4514`		`- */`
`4515`		`-if (naggs!=aggstate->numaggs)`
`4516`		`-ereport(ERROR,`
`4517`		`-(errcode(ERRCODE_GROUPING_ERROR),`
`4518`		`-errmsg("aggregate function calls cannot be nested")));`
	`4498`	`+aggstate->numaggs++;`
`4519`	`4499`	`}`
`4520`	`4500`	`else`
`4521`	`4501`	`{`

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Commit804163b

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8 files changed

8 files changed

`‎src/backend/executor/execQual.c`

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