]> granicus.if.org Git - postgresql/commitdiff
Avoid leaking memory while evaluating arguments for a table function.
authorTom Lane <tgl@sss.pgh.pa.us>
Fri, 20 Jun 2014 02:13:44 +0000 (22:13 -0400)
committerTom Lane <tgl@sss.pgh.pa.us>
Fri, 20 Jun 2014 02:13:44 +0000 (22:13 -0400)
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
src/backend/executor/nodeFunctionscan.c
src/include/executor/executor.h
src/include/nodes/execnodes.h

index f162e92fc713dba9f678f02909a54516cb2a512c..bc79e3aa00c90b5dee639b300ac24c546f1473c3 100644 (file)
@@ -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,
index da5d8c114dbe692764b5461f365fe06387267924..945a414e96fb29aeb9373c096a4e7dd6c3d7b193 100644 (file)
@@ -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;
 }
 
index 5e4a15ca74706c6d25d75344291677c03533988e..239aff3208827fc5ae01b44c3c5e90ef5e129cb4 100644 (file)
@@ -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,
index 0ab2a13697647f954f5264a5350612acfcc3269b..fae281143faa7724aa177b80083ab66bb84b9a31 100644 (file)
@@ -1406,6 +1406,7 @@ 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;
@@ -1420,6 +1421,7 @@ typedef struct FunctionScanState
        int                     nfuncs;
        struct FunctionScanPerFuncState *funcstates;            /* array of length
                                                                                                                 * nfuncs */
+       MemoryContext argcontext;
 } FunctionScanState;
 
 /* ----------------