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Commit83131e6

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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 parentb5c9a3b commit83131e6

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4 files changed

+29
-4
lines changed

4 files changed

+29
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lines changed

‎src/backend/executor/execQual.c

Lines changed: 11 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -1985,6 +1985,7 @@ ExecMakeFunctionResultNoSets(FuncExprState *fcache,
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Tuplestorestate*
19861986
ExecMakeTableFunctionResult(ExprState*funcexpr,
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ExprContext*econtext,
1988+
MemoryContextargContext,
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TupleDescexpectedDesc,
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boolrandomAccess)
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{
@@ -2063,13 +2064,19 @@ ExecMakeTableFunctionResult(ExprState *funcexpr,
20632064
/*
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* Evaluate the function's argument list.
20652066
*
2066-
* Note: ideally, we'd do this in the per-tuple context, but then the
2067-
* argument values would disappear when we reset the context in the
2068-
* inner loop. So do it in caller context. Perhaps we should make a
2069-
* separate context just to hold the evaluated arguments?
2067+
* We can't do this in the per-tuple context: the argument values
2068+
* would disappear when we reset that context in the inner loop. And
2069+
* the caller's CurrentMemoryContext is typically a query-lifespan
2070+
* context, so we don't want to leak memory there. We require the
2071+
* caller to pass a separate memory context that can be used for this,
2072+
* and can be reset each time through to avoid bloat.
20702073
*/
2074+
MemoryContextReset(argContext);
2075+
oldcontext=MemoryContextSwitchTo(argContext);
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fcinfo.flinfo=&(fcache->func);
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argDone=ExecEvalFuncArgs(&fcinfo,fcache->args,econtext);
2078+
MemoryContextSwitchTo(oldcontext);
2079+
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/* We don't allow sets in the arguments of the table function */
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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 @@
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#include"executor/nodeFunctionscan.h"
2626
#include"funcapi.h"
2727
#include"utils/builtins.h"
28+
#include"utils/memutils.h"
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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
}
@@ -223,6 +225,19 @@ ExecInitFunctionScan(FunctionScan *node, EState *estate, int eflags)
223225
ExecAssignResultTypeFromTL(&scanstate->ss.ps);
224226
ExecAssignScanProjectionInfo(&scanstate->ss);
225227

228+
/*
229+
* Create a memory context that ExecMakeTableFunctionResult can use to
230+
* evaluate function arguments in. We can't use the per-tuple context for
231+
* this because it gets reset too often; but we don't want to leak
232+
* evaluation results into the query-lifespan context either. We just
233+
* need one context, because we evaluate each function separately.
234+
*/
235+
scanstate->argcontext=AllocSetContextCreate(CurrentMemoryContext,
236+
"Table function arguments",
237+
ALLOCSET_DEFAULT_MINSIZE,
238+
ALLOCSET_DEFAULT_INITSIZE,
239+
ALLOCSET_DEFAULT_MAXSIZE);
240+
226241
returnscanstate;
227242
}
228243

‎src/include/executor/executor.h

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -207,6 +207,7 @@ extern Datum GetAttributeByName(HeapTupleHeader tuple, const char *attname,
207207
bool*isNull);
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externTuplestorestate*ExecMakeTableFunctionResult(ExprState*funcexpr,
209209
ExprContext*econtext,
210+
MemoryContextargContext,
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TupleDescexpectedDesc,
211212
boolrandomAccess);
212213
externDatumExecEvalExprSwitchContext(ExprState*expression,ExprContext*econtext,

‎src/include/nodes/execnodes.h

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1315,6 +1315,7 @@ typedef struct SubqueryScanState
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*tupdescexpected return tuple description
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*tuplestorestateprivate state of tuplestore.c
13171317
*funcexprstate for function expression being evaluated
1318+
*argcontextmemory context to evaluate function arguments in
13181319
* ----------------
13191320
*/
13201321
typedefstructFunctionScanState
@@ -1324,6 +1325,7 @@ typedef struct FunctionScanState
13241325
TupleDesctupdesc;
13251326
Tuplestorestate*tuplestorestate;
13261327
ExprState*funcexpr;
1328+
MemoryContextargcontext;
13271329
}FunctionScanState;
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13291331
/* ----------------

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