Hi, When I am working on "shared detoast value"[0], where I want to avoid detoast the same datum over and over again, I have to decide which memory context should be used to hold the detoast value. later I found I have to use different MemoryContexts for the OuterTuple and innerTuple since OuterTuple usually have a longer lifespan.
I found the following code in nodeMergeJoin.c which has pretty similar situation, just that it uses ExprContext rather than MemoryContext. MergeJoinState * ExecInitMergeJoin(MergeJoin *node, EState *estate, int eflags) /* * we need two additional econtexts in which we can compute the join * expressions from the left and right input tuples. The node's regular * econtext won't do because it gets reset too often. */ mergestate->mj_OuterEContext = CreateExprContext(estate); mergestate->mj_InnerEContext = CreateExprContext(estate); IIUC, we needs a MemoryContext rather than ExprContext in fact. In the attachment, I just use two MemoryContext instead of the two ExprContexts which should be less memory and more precise semantics, and works fine. shall we go in this direction? I attached the 2 MemoryContext in JoinState rather than MergeJoinState, which is for the "shared detoast value"[0] more or less. [0] https://www.postgresql.org/message-id/87ttoyihgm....@163.com
>From cadd94f8ff2398ca430b43494b3eb71225b017c3 Mon Sep 17 00:00:00 2001 From: "yizhi.fzh" <yizhi....@alibaba-inc.com> Date: Fri, 15 Dec 2023 15:28:36 +0800 Subject: [PATCH v1] Use MemoryContext instead of ExprContext for nodeMergejoin.c --- src/backend/executor/nodeMergejoin.c | 27 ++++++++++++++------------- src/backend/executor/nodeNestloop.c | 1 + src/include/nodes/execnodes.h | 4 ++-- 3 files changed, 17 insertions(+), 15 deletions(-) diff --git a/src/backend/executor/nodeMergejoin.c b/src/backend/executor/nodeMergejoin.c index 3cdab77dfc..d330e104f6 100644 --- a/src/backend/executor/nodeMergejoin.c +++ b/src/backend/executor/nodeMergejoin.c @@ -294,7 +294,7 @@ MJExamineQuals(List *mergeclauses, static MJEvalResult MJEvalOuterValues(MergeJoinState *mergestate) { - ExprContext *econtext = mergestate->mj_OuterEContext; + ExprContext *econtext = mergestate->js.ps.ps_ExprContext; MJEvalResult result = MJEVAL_MATCHABLE; int i; MemoryContext oldContext; @@ -303,9 +303,9 @@ MJEvalOuterValues(MergeJoinState *mergestate) if (TupIsNull(mergestate->mj_OuterTupleSlot)) return MJEVAL_ENDOFJOIN; - ResetExprContext(econtext); + MemoryContextReset(mergestate->js.outer_tuple_memory); - oldContext = MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory); + oldContext = MemoryContextSwitchTo(mergestate->js.outer_tuple_memory); econtext->ecxt_outertuple = mergestate->mj_OuterTupleSlot; @@ -341,7 +341,7 @@ MJEvalOuterValues(MergeJoinState *mergestate) static MJEvalResult MJEvalInnerValues(MergeJoinState *mergestate, TupleTableSlot *innerslot) { - ExprContext *econtext = mergestate->mj_InnerEContext; + ExprContext *econtext = mergestate->js.ps.ps_ExprContext; MJEvalResult result = MJEVAL_MATCHABLE; int i; MemoryContext oldContext; @@ -352,7 +352,7 @@ MJEvalInnerValues(MergeJoinState *mergestate, TupleTableSlot *innerslot) ResetExprContext(econtext); - oldContext = MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory); + oldContext = MemoryContextSwitchTo(mergestate->js.inner_tuple_memory); econtext->ecxt_innertuple = innerslot; @@ -1471,14 +1471,6 @@ ExecInitMergeJoin(MergeJoin *node, EState *estate, int eflags) */ ExecAssignExprContext(estate, &mergestate->js.ps); - /* - * we need two additional econtexts in which we can compute the join - * expressions from the left and right input tuples. The node's regular - * econtext won't do because it gets reset too often. - */ - mergestate->mj_OuterEContext = CreateExprContext(estate); - mergestate->mj_InnerEContext = CreateExprContext(estate); - /* * initialize child nodes * @@ -1497,6 +1489,15 @@ ExecInitMergeJoin(MergeJoin *node, EState *estate, int eflags) (eflags | EXEC_FLAG_MARK)); innerDesc = ExecGetResultType(innerPlanState(mergestate)); + mergestate->js.outer_tuple_memory = AllocSetContextCreate( + mergestate->js.ps.ps_ExprContext->ecxt_per_query_memory, + "OuterTupleCtx", + ALLOCSET_SMALL_SIZES); + mergestate->js.inner_tuple_memory = AllocSetContextCreate( + mergestate->js.ps.ps_ExprContext->ecxt_per_query_memory, + "InnerTupleCtx", + ALLOCSET_SMALL_SIZES); + /* * For certain types of inner child nodes, it is advantageous to issue * MARK every time we advance past an inner tuple we will never return to. diff --git a/src/backend/executor/nodeNestloop.c b/src/backend/executor/nodeNestloop.c index ebd1406843..5e10d01c4e 100644 --- a/src/backend/executor/nodeNestloop.c +++ b/src/backend/executor/nodeNestloop.c @@ -349,6 +349,7 @@ ExecInitNestLoop(NestLoop *node, EState *estate, int eflags) NL1_printf("ExecInitNestLoop: %s\n", "node initialized"); + return nlstate; } diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h index 5d7f17dee0..c0d4958ba2 100644 --- a/src/include/nodes/execnodes.h +++ b/src/include/nodes/execnodes.h @@ -2003,6 +2003,8 @@ typedef struct JoinState bool single_match; /* True if we should skip to next outer tuple * after finding one inner match */ ExprState *joinqual; /* JOIN quals (in addition to ps.qual) */ + MemoryContext outer_tuple_memory; + MemoryContext inner_tuple_memory; } JoinState; /* ---------------- @@ -2064,8 +2066,6 @@ typedef struct MergeJoinState TupleTableSlot *mj_MarkedTupleSlot; TupleTableSlot *mj_NullOuterTupleSlot; TupleTableSlot *mj_NullInnerTupleSlot; - ExprContext *mj_OuterEContext; - ExprContext *mj_InnerEContext; } MergeJoinState; /* ---------------- -- 2.34.1
-- Best Regards Andy Fan