8000 Avoid leaking memory while evaluating arguments for a table function. · hackingwu/postgres@d297c91 · GitHub
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Avoid leaking memory while evaluating arguments for a table function.
ExecMakeTableFunctionResult evaluated the arguments for a function-in-FROM in the query-lifespan memory context. This is insignificant in simple cases where the function relation is scanned only once; but if the function is in a sub-SELECT or is on the inside of a nested loop, any memory consumed during argument evaluation can add up quickly. (The potential for trouble here had been foreseen long ago, per existing comments; but we'd not previously seen a complaint from the field about it.) To fix, create an additional temporary context just for this purpose. Per an example from MauMau. Back-patch to all active branches.
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4 files changed

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‎src/backend/executor/execQual.c

Lines changed: 11 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -1935,6 +1935,7 @@ ExecMakeFunctionResultNoSets(FuncExprState *fcache,
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Tuplestorestate *
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ExecMakeTableFunctionResult(ExprState *funcexpr,
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ExprContext *econtext,
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MemoryContext argContext,
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TupleDesc expectedDesc,
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bool randomAccess)
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{
@@ -2013,13 +2014,19 @@ ExecMakeTableFunctionResult(ExprState *funcexpr,
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/*
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* Evaluate the function's argument list.
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*
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* Note: ideally, we'd do this in the per-tuple context, but then the
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* argument values would disappear when we reset the context in the
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* inner loop. So do it in caller context. Perhaps we should make a
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* separate context just to hold the evaluated arguments?
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* We can't do this in the per-tuple context: the argument values
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* would disappear when we reset that context in the inner loop. And
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* the caller's CurrentMemoryContext is typically a query-lifespan
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* context, so we don't want to leak memory there. We require the
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* caller to pass a separate memory context that can be used for this,
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* and can be reset each time through to avoid bloat.
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*/
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MemoryContextReset(argContext);
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oldcontext = MemoryContextSwitchTo(argContext);
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fcinfo.flinfo = &(fcache->func);
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argDone = ExecEvalFuncArgs(&fcinfo, fcache->args, econtext);
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MemoryContextSwitchTo(oldcontext);
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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"
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#include "funcapi.h"
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#include "utils/builtins.h"
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#include "utils/memutils.h"
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static TupleTableSlot *FunctionNext(FunctionScanState *node);
@@ -64,6 +65,7 @@ FunctionNext(FunctionScanState *node)
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node->tuplestorestate = tuplestorestate =
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ExecMakeTableFunctionResult(node->funcexpr,
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node->ss.ps.ps_ExprContext,
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node->argcontext,
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node->tupdesc,
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node->eflags & EXEC_FLAG_BACKWARD);
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}
@@ -217,6 +219,19 @@ ExecInitFunctionScan(FunctionScan *node, EState *estate, int eflags)
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ExecAssignResultTypeFromTL(&scanstate->ss.ps);
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ExecAssignScanProjectionInfo(&scanstate->ss);
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/*
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* Create a memory context that ExecMakeTableFunctionResult can use to
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* evaluate function arguments in. We can't use the per-tuple context for
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* this because it gets reset too often; but we don't want to leak
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* evaluation results into the query-lifespan context either. We just
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* need one context, because we evaluate each function separately.
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*/
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scanstate->argcontext = AllocSetContextCreate(CurrentMemoryContext,
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"Table function arguments",
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ALLOCSET_DEFAULT_MINSIZE,
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ALLOCSET_DEFAULT_INITSIZE,
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ALLOCSET_DEFAULT_MAXSIZE);
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return scanstate;
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}
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‎src/include/executor/executor.h

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -188,6 +188,7 @@ extern Datum GetAttributeByName(HeapTupleHeader tuple, const char *attname,
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bool *isNull);
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extern Tuplestorestate *ExecMakeTableFunctionResult(ExprState *funcexpr,
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ExprContext *econtext,
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MemoryContext argContext,
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TupleDesc expectedDesc,
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bool randomAccess);
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extern Datum ExecEvalExprSwitchContext(ExprState *expression, ExprContext *econtext,

‎src/include/nodes/execnodes.h

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1240,6 +1240,7 @@ typedef struct SubqueryScanState
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* tupdesc expected return tuple description
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* tuplestorestate private state of tuplestore.c
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* funcexpr state for function expression being evaluated
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* argcontext memory context to evaluate function arguments in
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* ----------------
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*/
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typedef struct FunctionScanState
@@ -1249,6 +1250,7 @@ typedef struct FunctionScanState
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TupleDesc tupdesc;
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Tuplestorestate *tuplestorestate;
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ExprState *funcexpr;
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MemoryContext argcontext;
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} FunctionScanState;
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/* ----------------

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