Re: Hybrid Hash/Nested Loop joins and caching results from subplans - Mailing list pgsql-hackers

I run your test case on v8 and v9,  I can produce a stable difference between them. 

v9: 

statement latencies in milliseconds:
      1772.287  select count(*) from hundredk hk inner join lookup l on hk.thousand = l.a;

then I did a perf on the 2 version,  Is it possible that you called tts_minimal_clear twice in 

the v9 version?  Both ExecClearTuple and  ExecStoreMinimalTuple called tts_minimal_clear

on the same  slot. 

With the following changes:

diff --git a/src/backend/executor/execMRUTupleCache.c b/src/backend/executor/execMRUTupleCache.c
index 3553dc26cb..b82d8e98b8 100644
--- a/src/backend/executor/execMRUTupleCache.c
+++ b/src/backend/executor/execMRUTupleCache.c
@@ -203,10 +203,9 @@ prepare_probe_slot(MRUTupleCache *mrucache, MRUCacheKey *key)
        TupleTableSlot *tslot = mrucache->tableslot;
        int                             numKeys = mrucache->nkeys;

-       ExecClearTuple(pslot);
-
        if (key == NULL)
        {
+               ExecClearTuple(pslot);
                /* Set the probeslot's values based on the current parameter values */
                for (int i = 0; i < numKeys; i++)
                        pslot->tts_values[i] = ExecEvalExpr(mrucache->param_exprs[i],
@@ -641,7 +640,7 @@ ExecMRUTupleCacheFetch(MRUTupleCache *mrucache)
                                        {
                                                mrucache->state = MRUCACHE_FETCH_NEXT_TUPLE;

-                                               ExecClearTuple(mrucache->cachefoundslot);
+                                               // ExecClearTuple(mrucache->cachefoundslot);
                                                slot = mrucache->cachefoundslot;
                                                ExecStoreMinimalTuple(mrucache->last_tuple->mintuple, slot, false);
                                                return slot;
@@ -740,7 +739,7 @@ ExecMRUTupleCacheFetch(MRUTupleCache *mrucache)
                                        return NULL;
                                }

-                               ExecClearTuple(mrucache->cachefoundslot);
+                               // ExecClearTuple(mrucache->cachefoundslot);
                                slot = mrucache->cachefoundslot;
                                ExecStoreMinimalTuple(mrucache->last_tuple->mintuple, slot, false);
                                return slot;

v9 has the following result:

      1608.048  select count(*) from hundredk hk inner join lookup l on hk.thousand = l.a;