From 45b0f357235236dd3198f8abcca277adc0d7459a Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Thu, 19 Jun 2014 22:13:41 -0400
Subject: [PATCH] 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.
---
src/backend/executor/execQual.c | 15 +++++++++++----
src/backend/executor/nodeFunctionscan.c | 16 ++++++++++++++++
src/include/executor/executor.h | 1 +
src/include/nodes/execnodes.h | 2 ++
4 files changed, 30 insertions(+), 4 deletions(-)
diff --git a/src/backend/executor/execQual.c b/src/backend/executor/execQual.c
index f162e92fc71..bc79e3aa00c 100644
--- a/src/backend/executor/execQual.c
+++ b/src/backend/executor/execQual.c
@@ -2002,6 +2002,7 @@ ExecMakeFunctionResultNoSets(FuncExprState *fcache,
Tuplestorestate *
ExecMakeTableFunctionResult(ExprState *funcexpr,
ExprContext *econtext,
+ MemoryContext argContext,
TupleDesc expectedDesc,
bool randomAccess)
{
@@ -2083,12 +2084,18 @@ ExecMakeTableFunctionResult(ExprState *funcexpr,
/*
* Evaluate the function's argument list.
*
- * Note: ideally, we'd do this in the per-tuple context, but then the
- * argument values would disappear when we reset the context in the
- * inner loop. So do it in caller context. Perhaps we should make a
- * separate context just to hold the evaluated arguments?
+ * We can't do this in the per-tuple context: the argument values
+ * would disappear when we reset that context in the inner loop. And
+ * the caller's CurrentMemoryContext is typically a query-lifespan
+ * context, so we don't want to leak memory there. We require the
+ * caller to pass a separate memory context that can be used for this,
+ * and can be reset each time through to avoid bloat.
*/
+ MemoryContextReset(argContext);
+ oldcontext = MemoryContextSwitchTo(argContext);
argDone = ExecEvalFuncArgs(&fcinfo, fcache->args, econtext);
+ MemoryContextSwitchTo(oldcontext);
+
/* We don't allow sets in the arguments of the table function */
if (argDone != ExprSingleResult)
ereport(ERROR,
diff --git a/src/backend/executor/nodeFunctionscan.c b/src/backend/executor/nodeFunctionscan.c
index da5d8c114db..945a414e96f 100644
--- a/src/backend/executor/nodeFunctionscan.c
+++ b/src/backend/executor/nodeFunctionscan.c
@@ -28,6 +28,7 @@
#include "nodes/nodeFuncs.h"
#include "parser/parsetree.h"
#include "utils/builtins.h"
+#include "utils/memutils.h"
/*
@@ -94,6 +95,7 @@ FunctionNext(FunctionScanState *node)
node->funcstates[0].tstore = tstore =
ExecMakeTableFunctionResult(node->funcstates[0].funcexpr,
node->ss.ps.ps_ExprContext,
+ node->argcontext,
node->funcstates[0].tupdesc,
node->eflags & EXEC_FLAG_BACKWARD);
@@ -152,6 +154,7 @@ FunctionNext(FunctionScanState *node)
fs->tstore =
ExecMakeTableFunctionResult(fs->funcexpr,
node->ss.ps.ps_ExprContext,
+ node->argcontext,
fs->tupdesc,
node->eflags & EXEC_FLAG_BACKWARD);
@@ -515,6 +518,19 @@ ExecInitFunctionScan(FunctionScan *node, EState *estate, int eflags)
ExecAssignResultTypeFromTL(&scanstate->ss.ps);
ExecAssignScanProjectionInfo(&scanstate->ss);
+ /*
+ * Create a memory context that ExecMakeTableFunctionResult can use to
+ * evaluate function arguments in. We can't use the per-tuple context for
+ * this because it gets reset too often; but we don't want to leak
+ * evaluation results into the query-lifespan context either. We just
+ * need one context, because we evaluate each function separately.
+ */
+ scanstate->argcontext = AllocSetContextCreate(CurrentMemoryContext,
+ "Table function arguments",
+ ALLOCSET_DEFAULT_MINSIZE,
+ ALLOCSET_DEFAULT_INITSIZE,
+ ALLOCSET_DEFAULT_MAXSIZE);
+
return scanstate;
}
diff --git a/src/include/executor/executor.h b/src/include/executor/executor.h
index 5e4a15ca747..239aff32088 100644
--- a/src/include/executor/executor.h
+++ b/src/include/executor/executor.h
@@ -231,6 +231,7 @@ extern Datum GetAttributeByName(HeapTupleHeader tuple, const char *attname,
bool *isNull);
extern Tuplestorestate *ExecMakeTableFunctionResult(ExprState *funcexpr,
ExprContext *econtext,
+ MemoryContext argContext,
TupleDesc expectedDesc,
bool randomAccess);
extern Datum ExecEvalExprSwitchContext(ExprState *expression, ExprContext *econtext,
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 1f7c6d13144..b271f213f59 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -1407,6 +1407,7 @@ typedef struct SubqueryScanState
* nfuncs number of functions being executed
* funcstates per-function execution states (private in
* nodeFunctionscan.c)
+ * argcontext memory context to evaluate function arguments in
* ----------------
*/
struct FunctionScanPerFuncState;
@@ -1421,6 +1422,7 @@ typedef struct FunctionScanState
int nfuncs;
struct FunctionScanPerFuncState *funcstates; /* array of length
* nfuncs */
+ MemoryContext argcontext;
} FunctionScanState;
/* ----------------
--
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