Re: Hash support for grouping sets

The following review has been posted through the commitfest application:
make installcheck-world: tested, failed
Implements feature: not tested
Spec compliant: not tested
Documentation: not tested

On linux/gcc the patch generates a warning in nodeAgg.c that is fairly easy
to fix. Using -Werror to make catching the error easier, I get:

make[3]: Entering directory `/home/mark/postgresql.clean/src/backend/executor'
gcc -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -O2 -Werror -I../../../src/include -D_GNU_SOURCE -c -o nodeAgg.o nodeAgg.c -MMD -MP -MF .deps/nodeAgg.Po
cc1: warnings being treated as errors
nodeAgg.c: In function ‘ExecAgg’:
nodeAgg.c:2053: error: ‘result’ may be used uninitialized in this function
make[3]: *** [nodeAgg.o] Error 1
make[3]: Leaving directory `/home/mark/postgresql.clean/src/backend/executor'
make[2]: *** [executor-recursive] Error 2
make[2]: Leaving directory `/home/mark/postgresql.clean/src/backend'
make[1]: *** [all-backend-recurse] Error 2
make[1]: Leaving directory `/home/mark/postgresql.clean/src'
make: *** [all-src-recurse] Error 2

There are two obvious choices to silence the warning:

diff --git a/src/backend/executor/nodeAgg.c b/src/backend/executor/nodeAgg.c
index f059560..8959f5b 100644
--- a/src/backend/executor/nodeAgg.c
+++ b/src/backend/executor/nodeAgg.c
@@ -2066,6 +2066,7 @@ ExecAgg(AggState *node)
break;
case AGG_PLAIN:
case AGG_SORTED:
+ default:
result = agg_retrieve_direct(node);
break;
}

which I like better, because I don't expect it would create
an extra instruction in the compiled code, but also:

diff --git a/src/backend/executor/nodeAgg.c b/src/backend/executor/nodeAgg.c
index f059560..eab2605 100644
--- a/src/backend/executor/nodeAgg.c
+++ b/src/backend/executor/nodeAgg.c
@@ -2050,7 +2050,7 @@ lookup_hash_entries(AggState *aggstate)
TupleTableSlot *
ExecAgg(AggState *node)
{
- TupleTableSlot *result;
+ TupleTableSlot *result = NULL;

if (!node->agg_done)
{