From: Ronan Dunklau <ronan.dunklau@aiven.io>
To: David Rowley <dgrowleyml@gmail.com>
Cc: Ranier Vilela <ranier.vf@gmail.com>
Cc: PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Cc: Dilip Kumar <dilipbalaut@gmail.com>
Cc: James Coleman <jtc331@gmail.com>
Subject: Re: [PATCH] Use optimized single-datum tuplesort in ExecSort
Date: Thu, 15 Jul 2021 16:53:29 +0200
Message-ID: <13249598.64SMogt8gv@aivenronan> (raw)
In-Reply-To: <CAApHDvprO=D-R63bdcw6OE1zhcqme2C5AAPhE=Qj8_zKJWG_Ww@mail.gmail.com>
References: <3177670.itZtoPt7T5@aivenronan>
<CAAaqYe8=rw2_RYr6xrFq6u-f-S4OryCg1OPJfxi-_JPeSmtQVg@mail.gmail.com>
<CAApHDvprO=D-R63bdcw6OE1zhcqme2C5AAPhE=Qj8_zKJWG_Ww@mail.gmail.com>
Le jeudi 15 juillet 2021, 16:19:23 CEST David Rowley a écrit :>
> Ronan's latest results plus John's make me think there's no need to
> separate out the node function as I did in v8. However, I do think v6
> could learn a little from v8. I think I'd rather see the sort method
> determined in ExecInitSort() rather than ExecSort(). I think
> minimising those few extra instructions in ExecSort() might help the
> L1 instruction cache.
>
I'm not sure I understand what you expect from moving that to ExecInitSort ?
Maybe we should also implement the tuplesort_state initialization in
ExecInitSort ? (not the actual feeding and sorting of course).
Please find attached a v9 just moving the flag setting to ExecInitSort, and my
apologies if I misunderstood your point.
--
Ronan Dunklau
Attachments:v9-0001-Allow-Sort-nodes-to-use-the-fast-single-datum-tuples.patch (text/x-patch, 5.0K) download
commit 2bf8db23c8ddb53f7dbcba33c60350bda9d703ea
Author: Ronan Dunklau <ronan.dunklau@aiven.io>
Date: Tue Jul 6 16:34:31 2021 +0200
Use optimized single-datum tuplesort in ExecSort
Previously, with optimization was only done in ExecAgg.
Doing this optimization on regular sort nodes provides for a nice
performance improvement, when the input / output tuple has only one
attribute.
diff --git a/src/backend/executor/nodeSort.c b/src/backend/executor/nodeSort.cindex b99027e0d7..861e4c6e9e 100644--- a/src/backend/executor/nodeSort.c+++ b/src/backend/executor/nodeSort.c@@ -29,6 +29,10 @@
* which saves the results in a temporary file or memory. After the
* initial call, returns a tuple from the file with each call.
*
+ * The tuplesort can either occur on the whole tuple (this is the nominal+ * case) or, when the input / output tuple consists of only one attribute,+ * we switch to the tuplesort_*_datum API, optimized for that specific case.+ *
* Conditions:
* -- none.
*
@@ -86,31 +90,63 @@ ExecSort(PlanState *pstate)
outerNode = outerPlanState(node);
tupDesc = ExecGetResultType(outerNode);
- tuplesortstate = tuplesort_begin_heap(tupDesc,- plannode->numCols,- plannode->sortColIdx,- plannode->sortOperators,- plannode->collations,- plannode->nullsFirst,- work_mem,- NULL,- node->randomAccess);+ /*+ * Switch to the tuplesort_*_datum interface when we have only one+ * key, as it is much more efficient especially when the type is+ * pass-by-value.+ */+ if (node->datumSort)+ {+ tuplesortstate = tuplesort_begin_datum(TupleDescAttr(tupDesc, 0)->atttypid,+ plannode->sortOperators[0],+ plannode->collations[0],+ plannode->nullsFirst[0],+ work_mem,+ NULL,+ node->randomAccess);+ }+ else+ tuplesortstate = tuplesort_begin_heap(tupDesc,+ plannode->numCols,+ plannode->sortColIdx,+ plannode->sortOperators,+ plannode->collations,+ plannode->nullsFirst,+ work_mem,+ NULL,+ node->randomAccess);
if (node->bounded)
tuplesort_set_bound(tuplesortstate, node->bound);
node->tuplesortstate = (void *) tuplesortstate;
/*
- * Scan the subplan and feed all the tuples to tuplesort.+ * Scan the subplan and feed all the tuples to tuplesort, using either+ * the _putdatum or _puttupleslot API as appropriate.
*/
-- for (;;)+ if (node->datumSort)
{
- slot = ExecProcNode(outerNode);-- if (TupIsNull(slot))- break;-- tuplesort_puttupleslot(tuplesortstate, slot);+ for (;;)+ {+ slot = ExecProcNode(outerNode);++ if (TupIsNull(slot))+ break;+ slot_getsomeattrs(slot, 1);+ tuplesort_putdatum(tuplesortstate,+ slot->tts_values[0],+ slot->tts_isnull[0]);+ }+ }+ else+ {+ for (;;)+ {+ slot = ExecProcNode(outerNode);++ if (TupIsNull(slot))+ break;+ tuplesort_puttupleslot(tuplesortstate, slot);+ }
}
/*
@@ -150,9 +186,18 @@ ExecSort(PlanState *pstate)
* next fetch from the tuplesort.
*/
slot = node->ss.ps.ps_ResultTupleSlot;
- (void) tuplesort_gettupleslot(tuplesortstate,- ScanDirectionIsForward(dir),- false, slot, NULL);+ if (node->datumSort)+ {+ ExecClearTuple(slot);+ if (tuplesort_getdatum(tuplesortstate, ScanDirectionIsForward(dir),+ &(slot->tts_values[0]), &(slot->tts_isnull[0]), NULL))+ ExecStoreVirtualTuple(slot);+ }+ else+ (void) tuplesort_gettupleslot(tuplesortstate,+ ScanDirectionIsForward(dir),+ false, slot, NULL);+
return slot;
}
@@ -191,6 +236,7 @@ ExecInitSort(Sort *node, EState *estate, int eflags)
sortstate->bounded = false;
sortstate->sort_Done = false;
sortstate->tuplesortstate = NULL;
+ sortstate->datumSort = false;
/*
* Miscellaneous initialization
@@ -220,6 +266,15 @@ ExecInitSort(Sort *node, EState *estate, int eflags)
*/
ExecInitResultTupleSlotTL(&sortstate->ss.ps, &TTSOpsMinimalTuple);
sortstate->ss.ps.ps_ProjInfo = NULL;
+ + /*+ * We perform a Datum sort when we're sorting just a single column,+ * otherwise we perform a tuple sort.+ */+ if (ExecGetResultType(outerPlanState(sortstate))->natts == 1)+ sortstate->datumSort = true;+ else+ sortstate->datumSort = false;
SO1_printf("ExecInitSort: %s\n",
"sort node initialized");
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.hindex 0ec5509e7e..89f944a9c4 100644--- a/src/include/nodes/execnodes.h+++ b/src/include/nodes/execnodes.h@@ -2151,6 +2151,7 @@ typedef struct SortState
int64 bound_Done; /* value of bound we did the sort with */
void *tuplesortstate; /* private state of tuplesort.c */
bool am_worker; /* are we a worker? */
+ bool datumSort; /* are we using the single value optimization ? */
SharedSortInfo *shared_info; /* one entry per worker */
} SortState;
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Cc: ronan.dunklau@aiven.io, dgrowleyml@gmail.com, ranier.vf@gmail.com, pgsql-hackers@lists.postgresql.org, dilipbalaut@gmail.com, jtc331@gmail.com
Subject: Re: [PATCH] Use optimized single-datum tuplesort in ExecSort
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