From 908a968612f9ed61911d8ca0a185b262b82f1269 Mon Sep 17 00:00:00 2001 From: David Rowley Date: Thu, 5 Sep 2024 16:18:30 +1200 Subject: [PATCH] Optimize WindowAgg's use of tuplestores When WindowAgg finished one partition of a PARTITION BY, it previously would call tuplestore_end() to purge all the stored tuples before again calling tuplestore_begin_heap() and carefully setting up all of the tuplestore read pointers exactly as required for the given frameOptions. Since the frameOptions don't change between partitions, this part does not make much sense. For queries that had very few rows per partition, the overhead of this was very large. It seems much better to create the tuplestore and the read pointers once and simply call tuplestore_clear() at the end of each partition. tuplestore_clear() moves all of the read pointers back to the start position and deletes all the previously stored tuples. A simple test query with 1 million partitions and 1 tuple per partition has been shown to run around 40% faster than without this change. The additional effort seems to have mostly been spent in malloc/free. Making this work required adding a new bool field to WindowAggState which had the unfortunate effect of being the 9th bool field in a group resulting in the struct being enlarged. Here we shuffle the fields around a little so that the two bool fields for runcondition relating stuff fit into existing padding. Also, move the "runcondition" field to be near those. This frees up enough space with the other bool fields so that the newly added one fits into the padding bytes. This was done to address a very small but apparent performance regression with queries containing a large number of rows per partition. Reviewed-by: Ashutosh Bapat Reviewed-by: Tatsuo Ishii Discussion: https://postgr.es/m/CAHoyFK9n-QCXKTUWT_xxtXninSMEv%2BgbJN66-y6prM3f4WkEHw%40mail.gmail.com --- src/backend/executor/nodeWindowAgg.c | 162 ++++++++++++++++++--------- src/include/nodes/execnodes.h | 22 ++-- 2 files changed, 118 insertions(+), 66 deletions(-) diff --git a/src/backend/executor/nodeWindowAgg.c b/src/backend/executor/nodeWindowAgg.c index 88a85f556b6..51a6708a392 100644 --- a/src/backend/executor/nodeWindowAgg.c +++ b/src/backend/executor/nodeWindowAgg.c @@ -1074,57 +1074,24 @@ eval_windowfunction(WindowAggState *winstate, WindowStatePerFunc perfuncstate, } /* - * begin_partition - * Start buffering rows of the next partition. + * prepare_tuplestore + * Prepare the tuplestore and all of the required read pointers for the + * WindowAggState's frameOptions. + * + * Note: We use pg_noinline to avoid bloating the calling function with code + * which is only called once. */ -static void -begin_partition(WindowAggState *winstate) +static pg_noinline void +prepare_tuplestore(WindowAggState *winstate) { WindowAgg *node = (WindowAgg *) winstate->ss.ps.plan; - PlanState *outerPlan = outerPlanState(winstate); int frameOptions = winstate->frameOptions; int numfuncs = winstate->numfuncs; - int i; - - winstate->partition_spooled = false; - winstate->framehead_valid = false; - winstate->frametail_valid = false; - winstate->grouptail_valid = false; - winstate->spooled_rows = 0; - winstate->currentpos = 0; - winstate->frameheadpos = 0; - winstate->frametailpos = 0; - winstate->currentgroup = 0; - winstate->frameheadgroup = 0; - winstate->frametailgroup = 0; - winstate->groupheadpos = 0; - winstate->grouptailpos = -1; /* see update_grouptailpos */ - ExecClearTuple(winstate->agg_row_slot); - if (winstate->framehead_slot) - ExecClearTuple(winstate->framehead_slot); - if (winstate->frametail_slot) - ExecClearTuple(winstate->frametail_slot); - - /* - * If this is the very first partition, we need to fetch the first input - * row to store in first_part_slot. - */ - if (TupIsNull(winstate->first_part_slot)) - { - TupleTableSlot *outerslot = ExecProcNode(outerPlan); - if (!TupIsNull(outerslot)) - ExecCopySlot(winstate->first_part_slot, outerslot); - else - { - /* outer plan is empty, so we have nothing to do */ - winstate->partition_spooled = true; - winstate->more_partitions = false; - return; - } - } + /* we shouldn't be called if this was done already */ + Assert(winstate->buffer == NULL); - /* Create new tuplestore for this partition */ + /* Create new tuplestore */ winstate->buffer = tuplestore_begin_heap(false, false, work_mem); /* @@ -1158,16 +1125,10 @@ begin_partition(WindowAggState *winstate) agg_winobj->readptr = tuplestore_alloc_read_pointer(winstate->buffer, readptr_flags); - agg_winobj->markpos = -1; - agg_winobj->seekpos = -1; - - /* Also reset the row counters for aggregates */ - winstate->aggregatedbase = 0; - winstate->aggregatedupto = 0; } /* create mark and read pointers for each real window function */ - for (i = 0; i < numfuncs; i++) + for (int i = 0; i < numfuncs; i++) { WindowStatePerFunc perfuncstate = &(winstate->perfunc[i]); @@ -1179,8 +1140,6 @@ begin_partition(WindowAggState *winstate) 0); winobj->readptr = tuplestore_alloc_read_pointer(winstate->buffer, EXEC_FLAG_BACKWARD); - winobj->markpos = -1; - winobj->seekpos = -1; } } @@ -1224,6 +1183,88 @@ begin_partition(WindowAggState *winstate) winstate->grouptail_ptr = tuplestore_alloc_read_pointer(winstate->buffer, 0); } +} + +/* + * begin_partition + * Start buffering rows of the next partition. + */ +static void +begin_partition(WindowAggState *winstate) +{ + PlanState *outerPlan = outerPlanState(winstate); + int numfuncs = winstate->numfuncs; + + winstate->partition_spooled = false; + winstate->framehead_valid = false; + winstate->frametail_valid = false; + winstate->grouptail_valid = false; + winstate->spooled_rows = 0; + winstate->currentpos = 0; + winstate->frameheadpos = 0; + winstate->frametailpos = 0; + winstate->currentgroup = 0; + winstate->frameheadgroup = 0; + winstate->frametailgroup = 0; + winstate->groupheadpos = 0; + winstate->grouptailpos = -1; /* see update_grouptailpos */ + ExecClearTuple(winstate->agg_row_slot); + if (winstate->framehead_slot) + ExecClearTuple(winstate->framehead_slot); + if (winstate->frametail_slot) + ExecClearTuple(winstate->frametail_slot); + + /* + * If this is the very first partition, we need to fetch the first input + * row to store in first_part_slot. + */ + if (TupIsNull(winstate->first_part_slot)) + { + TupleTableSlot *outerslot = ExecProcNode(outerPlan); + + if (!TupIsNull(outerslot)) + ExecCopySlot(winstate->first_part_slot, outerslot); + else + { + /* outer plan is empty, so we have nothing to do */ + winstate->partition_spooled = true; + winstate->more_partitions = false; + return; + } + } + + /* Create new tuplestore if not done already. */ + if (unlikely(winstate->buffer == NULL)) + prepare_tuplestore(winstate); + + winstate->next_partition = false; + + if (winstate->numaggs > 0) + { + WindowObject agg_winobj = winstate->agg_winobj; + + /* reset mark and see positions for aggregate functions */ + agg_winobj->markpos = -1; + agg_winobj->seekpos = -1; + + /* Also reset the row counters for aggregates */ + winstate->aggregatedbase = 0; + winstate->aggregatedupto = 0; + } + + /* reset mark and seek positions for each real window function */ + for (int i = 0; i < numfuncs; i++) + { + WindowStatePerFunc perfuncstate = &(winstate->perfunc[i]); + + if (!perfuncstate->plain_agg) + { + WindowObject winobj = perfuncstate->winobj; + + winobj->markpos = -1; + winobj->seekpos = -1; + } + } /* * Store the first tuple into the tuplestore (it's always available now; @@ -1360,9 +1401,9 @@ release_partition(WindowAggState *winstate) } if (winstate->buffer) - tuplestore_end(winstate->buffer); - winstate->buffer = NULL; + tuplestore_clear(winstate->buffer); winstate->partition_spooled = false; + winstate->next_partition = true; } /* @@ -2143,7 +2184,7 @@ ExecWindowAgg(PlanState *pstate) /* We need to loop as the runCondition or qual may filter out tuples */ for (;;) { - if (winstate->buffer == NULL) + if (winstate->next_partition) { /* Initialize for first partition and set current row = 0 */ begin_partition(winstate); @@ -2686,6 +2727,7 @@ ExecInitWindowAgg(WindowAgg *node, EState *estate, int eflags) winstate->all_first = true; winstate->partition_spooled = false; winstate->more_partitions = false; + winstate->next_partition = true; return winstate; } @@ -2700,6 +2742,14 @@ ExecEndWindowAgg(WindowAggState *node) PlanState *outerPlan; int i; + if (node->buffer != NULL) + { + tuplestore_end(node->buffer); + + /* nullify so that release_partition skips the tuplestore_clear() */ + node->buffer = NULL; + } + release_partition(node); for (i = 0; i < node->numaggs; i++) diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h index af7d8fd1e72..627f99c13d1 100644 --- a/src/include/nodes/execnodes.h +++ b/src/include/nodes/execnodes.h @@ -2619,6 +2619,17 @@ typedef struct WindowAggState bool inRangeAsc; /* use ASC sort order for in_range tests? */ bool inRangeNullsFirst; /* nulls sort first for in_range tests? */ + /* fields relating to runconditions */ + bool use_pass_through; /* When false, stop execution when + * runcondition is no longer true. Else + * just stop evaluating window funcs. */ + bool top_window; /* true if this is the top-most WindowAgg or + * the only WindowAgg in this query level */ + ExprState *runcondition; /* Condition which must remain true otherwise + * execution of the WindowAgg will finish or + * go into pass-through mode. NULL when there + * is no such condition. */ + /* these fields are used in GROUPS mode: */ int64 currentgroup; /* peer group # of current row in partition */ int64 frameheadgroup; /* peer group # of frame head row */ @@ -2631,19 +2642,10 @@ typedef struct WindowAggState MemoryContext curaggcontext; /* current aggregate's working data */ ExprContext *tmpcontext; /* short-term evaluation context */ - ExprState *runcondition; /* Condition which must remain true otherwise - * execution of the WindowAgg will finish or - * go into pass-through mode. NULL when there - * is no such condition. */ - - bool use_pass_through; /* When false, stop execution when - * runcondition is no longer true. Else - * just stop evaluating window funcs. */ - bool top_window; /* true if this is the top-most WindowAgg or - * the only WindowAgg in this query level */ bool all_first; /* true if the scan is starting */ bool partition_spooled; /* true if all tuples in current partition * have been spooled into tuplestore */ + bool next_partition; /* true if begin_partition needs to be called */ bool more_partitions; /* true if there's more partitions after * this one */ bool framehead_valid; /* true if frameheadpos is known up to -- 2.30.2