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Commit50a38f6

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Create memory context for HashAgg with a reasonable maxBlockSize.
If the memory context's maxBlockSize is too big, a single blockallocation can suddenly exceed work_mem. For Hash Aggregation, thiscan mean spilling to disk too early or reporting a confusing memoryusage number for EXPLAN ANALYZE.Introduce CreateWorkExprContext(), which is like CreateExprContext(),except that it creates the AllocSet with a maxBlockSize that isreasonable in proportion to work_mem.Right now, CreateWorkExprContext() is only used by Hash Aggregation,but it may be generally useful in the future.Discussion:https://postgr.es/m/412a3fbf306f84d8d78c4009e11791867e62b87c.camel@j-davis.com
1 parentf0705bb commit50a38f6

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3 files changed

+58
-19
lines changed

3 files changed

+58
-19
lines changed

‎src/backend/executor/execUtils.c

Lines changed: 56 additions & 15 deletions
Original file line numberDiff line numberDiff line change
@@ -53,6 +53,7 @@
5353
#include"executor/executor.h"
5454
#include"jit/jit.h"
5555
#include"mb/pg_wchar.h"
56+
#include"miscadmin.h"
5657
#include"nodes/nodeFuncs.h"
5758
#include"parser/parsetree.h"
5859
#include"partitioning/partdesc.h"
@@ -227,21 +228,13 @@ FreeExecutorState(EState *estate)
227228
MemoryContextDelete(estate->es_query_cxt);
228229
}
229230

230-
/* ----------------
231-
*CreateExprContext
232-
*
233-
*Create a context for expression evaluation within an EState.
234-
*
235-
* An executor run may require multiple ExprContexts (we usually make one
236-
* for each Plan node, and a separate one for per-output-tuple processing
237-
* such as constraint checking). Each ExprContext has its own "per-tuple"
238-
* memory context.
239-
*
240-
* Note we make no assumption about the caller's memory context.
241-
* ----------------
231+
/*
232+
* Internal implementation for CreateExprContext() and CreateWorkExprContext()
233+
* that allows control over the AllocSet parameters.
242234
*/
243-
ExprContext*
244-
CreateExprContext(EState*estate)
235+
staticExprContext*
236+
CreateExprContextInternal(EState*estate,SizeminContextSize,
237+
SizeinitBlockSize,SizemaxBlockSize)
245238
{
246239
ExprContext*econtext;
247240
MemoryContextoldcontext;
@@ -264,7 +257,9 @@ CreateExprContext(EState *estate)
264257
econtext->ecxt_per_tuple_memory=
265258
AllocSetContextCreate(estate->es_query_cxt,
266259
"ExprContext",
267-
ALLOCSET_DEFAULT_SIZES);
260+
minContextSize,
261+
initBlockSize,
262+
maxBlockSize);
268263

269264
econtext->ecxt_param_exec_vals=estate->es_param_exec_vals;
270265
econtext->ecxt_param_list_info=estate->es_param_list_info;
@@ -294,6 +289,52 @@ CreateExprContext(EState *estate)
294289
returnecontext;
295290
}
296291

292+
/* ----------------
293+
*CreateExprContext
294+
*
295+
*Create a context for expression evaluation within an EState.
296+
*
297+
* An executor run may require multiple ExprContexts (we usually make one
298+
* for each Plan node, and a separate one for per-output-tuple processing
299+
* such as constraint checking). Each ExprContext has its own "per-tuple"
300+
* memory context.
301+
*
302+
* Note we make no assumption about the caller's memory context.
303+
* ----------------
304+
*/
305+
ExprContext*
306+
CreateExprContext(EState*estate)
307+
{
308+
returnCreateExprContextInternal(estate,ALLOCSET_DEFAULT_SIZES);
309+
}
310+
311+
312+
/* ----------------
313+
*CreateWorkExprContext
314+
*
315+
* Like CreateExprContext, but specifies the AllocSet sizes to be reasonable
316+
* in proportion to work_mem. If the maximum block allocation size is too
317+
* large, it's easy to skip right past work_mem with a single allocation.
318+
* ----------------
319+
*/
320+
ExprContext*
321+
CreateWorkExprContext(EState*estate)
322+
{
323+
SizeminContextSize=ALLOCSET_DEFAULT_MINSIZE;
324+
SizeinitBlockSize=ALLOCSET_DEFAULT_INITSIZE;
325+
SizemaxBlockSize=ALLOCSET_DEFAULT_MAXSIZE;
326+
327+
/* choose the maxBlockSize to be no larger than 1/16 of work_mem */
328+
while (16*maxBlockSize>work_mem*1024L)
329+
maxBlockSize >>=1;
330+
331+
if (maxBlockSize<ALLOCSET_DEFAULT_INITSIZE)
332+
maxBlockSize=ALLOCSET_DEFAULT_INITSIZE;
333+
334+
returnCreateExprContextInternal(estate,minContextSize,
335+
initBlockSize,maxBlockSize);
336+
}
337+
297338
/* ----------------
298339
*CreateStandaloneExprContext
299340
*

‎src/backend/executor/nodeAgg.c

Lines changed: 1 addition & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -3277,10 +3277,7 @@ ExecInitAgg(Agg *node, EState *estate, int eflags)
32773277
}
32783278

32793279
if (use_hashing)
3280-
{
3281-
ExecAssignExprContext(estate,&aggstate->ss.ps);
3282-
aggstate->hashcontext=aggstate->ss.ps.ps_ExprContext;
3283-
}
3280+
aggstate->hashcontext=CreateWorkExprContext(estate);
32843281

32853282
ExecAssignExprContext(estate,&aggstate->ss.ps);
32863283

‎src/include/executor/executor.h

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -493,6 +493,7 @@ extern void end_tup_output(TupOutputState *tstate);
493493
externEState*CreateExecutorState(void);
494494
externvoidFreeExecutorState(EState*estate);
495495
externExprContext*CreateExprContext(EState*estate);
496+
externExprContext*CreateWorkExprContext(EState*estate);
496497
externExprContext*CreateStandaloneExprContext(void);
497498
externvoidFreeExprContext(ExprContext*econtext,boolisCommit);
498499
externvoidReScanExprContext(ExprContext*econtext);

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