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.

diff --git a/src/backend/executor/execQual.c b/src/backend/executor/execQual.c
index f162e92fc713dba9f678f02909a54516cb2a512c..bc79e3aa00c90b5dee639b300ac24c546f1473c3 100644 (file)
--- 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 da5d8c114dbe692764b5461f365fe06387267924..945a414e96fb29aeb9373c096a4e7dd6c3d7b193 100644 (file)
--- 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 5e4a15ca74706c6d25d75344291677c03533988e..239aff3208827fc5ae01b44c3c5e90ef5e129cb4 100644 (file)
--- 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 1f7c6d13144708abc9f3ceb9414255f95ab1e693..b271f213f597ec52d0488c0573c2ca64ef3670fb 100644 (file)
--- 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;
 
 /* ----------------