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Commitc1f8fb9

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Avoid leaking memory while evaluating arguments for a table function.
ExecMakeTableFunctionResult evaluated the arguments for a function-in-FROMin the query-lifespan memory context. This is insignificant in simplecases where the function relation is scanned only once; but if the functionis in a sub-SELECT or is on the inside of a nested loop, any memoryconsumed during argument evaluation can add up quickly. (The potential fortrouble here had been foreseen long ago, per existing comments; but we'dnot previously seen a complaint from the field about it.) To fix, createan additional temporary context just for this purpose.Per an example from MauMau. Back-patch to all active branches.
1 parent1442b42 commitc1f8fb9

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4 files changed

+29
-4
lines changed

4 files changed

+29
-4
lines changed

‎src/backend/executor/execQual.c

Lines changed: 11 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -2002,6 +2002,7 @@ ExecMakeFunctionResultNoSets(FuncExprState *fcache,
20022002
Tuplestorestate*
20032003
ExecMakeTableFunctionResult(ExprState*funcexpr,
20042004
ExprContext*econtext,
2005+
MemoryContextargContext,
20052006
TupleDescexpectedDesc,
20062007
boolrandomAccess)
20072008
{
@@ -2083,12 +2084,18 @@ ExecMakeTableFunctionResult(ExprState *funcexpr,
20832084
/*
20842085
* Evaluate the function's argument list.
20852086
*
2086-
* Note: ideally, we'd do this in the per-tuple context, but then the
2087-
* argument values would disappear when we reset the context in the
2088-
* inner loop. So do it in caller context. Perhaps we should make a
2089-
* separate context just to hold the evaluated arguments?
2087+
* We can't do this in the per-tuple context: the argument values
2088+
* would disappear when we reset that context in the inner loop. And
2089+
* the caller's CurrentMemoryContext is typically a query-lifespan
2090+
* context, so we don't want to leak memory there. We require the
2091+
* caller to pass a separate memory context that can be used for this,
2092+
* and can be reset each time through to avoid bloat.
20902093
*/
2094+
MemoryContextReset(argContext);
2095+
oldcontext=MemoryContextSwitchTo(argContext);
20912096
argDone=ExecEvalFuncArgs(&fcinfo,fcache->args,econtext);
2097+
MemoryContextSwitchTo(oldcontext);
2098+
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/* We don't allow sets in the arguments of the table function */
20932100
if (argDone!=ExprSingleResult)
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ereport(ERROR,

‎src/backend/executor/nodeFunctionscan.c

Lines changed: 15 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -25,6 +25,7 @@
2525
#include"executor/nodeFunctionscan.h"
2626
#include"funcapi.h"
2727
#include"nodes/nodeFuncs.h"
28+
#include"utils/memutils.h"
2829

2930

3031
staticTupleTableSlot*FunctionNext(FunctionScanState*node);
@@ -64,6 +65,7 @@ FunctionNext(FunctionScanState *node)
6465
node->tuplestorestate=tuplestorestate=
6566
ExecMakeTableFunctionResult(node->funcexpr,
6667
node->ss.ps.ps_ExprContext,
68+
node->argcontext,
6769
node->tupdesc,
6870
node->eflags&EXEC_FLAG_BACKWARD);
6971
}
@@ -227,6 +229,19 @@ ExecInitFunctionScan(FunctionScan *node, EState *estate, int eflags)
227229
ExecAssignResultTypeFromTL(&scanstate->ss.ps);
228230
ExecAssignScanProjectionInfo(&scanstate->ss);
229231

232+
/*
233+
* Create a memory context that ExecMakeTableFunctionResult can use to
234+
* evaluate function arguments in. We can't use the per-tuple context for
235+
* this because it gets reset too often; but we don't want to leak
236+
* evaluation results into the query-lifespan context either. We just
237+
* need one context, because we evaluate each function separately.
238+
*/
239+
scanstate->argcontext=AllocSetContextCreate(CurrentMemoryContext,
240+
"Table function arguments",
241+
ALLOCSET_DEFAULT_MINSIZE,
242+
ALLOCSET_DEFAULT_INITSIZE,
243+
ALLOCSET_DEFAULT_MAXSIZE);
244+
230245
returnscanstate;
231246
}
232247

‎src/include/executor/executor.h

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -229,6 +229,7 @@ extern Datum GetAttributeByName(HeapTupleHeader tuple, const char *attname,
229229
bool*isNull);
230230
externTuplestorestate*ExecMakeTableFunctionResult(ExprState*funcexpr,
231231
ExprContext*econtext,
232+
MemoryContextargContext,
232233
TupleDescexpectedDesc,
233234
boolrandomAccess);
234235
externDatumExecEvalExprSwitchContext(ExprState*expression,ExprContext*econtext,

‎src/include/nodes/execnodes.h

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1392,6 +1392,7 @@ typedef struct SubqueryScanState
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*tupdescexpected return tuple description
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*tuplestorestateprivate state of tuplestore.c
13941394
*funcexprstate for function expression being evaluated
1395+
*argcontextmemory context to evaluate function arguments in
13951396
* ----------------
13961397
*/
13971398
typedefstructFunctionScanState
@@ -1401,6 +1402,7 @@ typedef struct FunctionScanState
14011402
TupleDesctupdesc;
14021403
Tuplestorestate*tuplestorestate;
14031404
ExprState*funcexpr;
1405+
MemoryContextargcontext;
14041406
}FunctionScanState;
14051407

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/* ----------------

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