LCOV - code coverage report
Current view: top level - src/backend/executor - nodeGatherMerge.c (source / functions) Hit Total Coverage
Test: PostgreSQL 12beta2 Lines: 212 218 97.2 %
Date: 2019-06-19 16:07:09 Functions: 14 14 100.0 %
Legend: Lines: hit not hit

          Line data    Source code
       1             : /*-------------------------------------------------------------------------
       2             :  *
       3             :  * nodeGatherMerge.c
       4             :  *      Scan a plan in multiple workers, and do order-preserving merge.
       5             :  *
       6             :  * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
       7             :  * Portions Copyright (c) 1994, Regents of the University of California
       8             :  *
       9             :  * IDENTIFICATION
      10             :  *    src/backend/executor/nodeGatherMerge.c
      11             :  *
      12             :  *-------------------------------------------------------------------------
      13             :  */
      14             : 
      15             : #include "postgres.h"
      16             : 
      17             : #include "access/relscan.h"
      18             : #include "access/xact.h"
      19             : #include "executor/execdebug.h"
      20             : #include "executor/execParallel.h"
      21             : #include "executor/nodeGatherMerge.h"
      22             : #include "executor/nodeSubplan.h"
      23             : #include "executor/tqueue.h"
      24             : #include "lib/binaryheap.h"
      25             : #include "miscadmin.h"
      26             : #include "optimizer/optimizer.h"
      27             : #include "utils/memutils.h"
      28             : #include "utils/rel.h"
      29             : 
      30             : /*
      31             :  * When we read tuples from workers, it's a good idea to read several at once
      32             :  * for efficiency when possible: this minimizes context-switching overhead.
      33             :  * But reading too many at a time wastes memory without improving performance.
      34             :  * We'll read up to MAX_TUPLE_STORE tuples (in addition to the first one).
      35             :  */
      36             : #define MAX_TUPLE_STORE 10
      37             : 
      38             : /*
      39             :  * Pending-tuple array for each worker.  This holds additional tuples that
      40             :  * we were able to fetch from the worker, but can't process yet.  In addition,
      41             :  * this struct holds the "done" flag indicating the worker is known to have
      42             :  * no more tuples.  (We do not use this struct for the leader; we don't keep
      43             :  * any pending tuples for the leader, and the need_to_scan_locally flag serves
      44             :  * as its "done" indicator.)
      45             :  */
      46             : typedef struct GMReaderTupleBuffer
      47             : {
      48             :     HeapTuple  *tuple;          /* array of length MAX_TUPLE_STORE */
      49             :     int         nTuples;        /* number of tuples currently stored */
      50             :     int         readCounter;    /* index of next tuple to extract */
      51             :     bool        done;           /* true if reader is known exhausted */
      52             : } GMReaderTupleBuffer;
      53             : 
      54             : static TupleTableSlot *ExecGatherMerge(PlanState *pstate);
      55             : static int32 heap_compare_slots(Datum a, Datum b, void *arg);
      56             : static TupleTableSlot *gather_merge_getnext(GatherMergeState *gm_state);
      57             : static HeapTuple gm_readnext_tuple(GatherMergeState *gm_state, int nreader,
      58             :                                    bool nowait, bool *done);
      59             : static void ExecShutdownGatherMergeWorkers(GatherMergeState *node);
      60             : static void gather_merge_setup(GatherMergeState *gm_state);
      61             : static void gather_merge_init(GatherMergeState *gm_state);
      62             : static void gather_merge_clear_tuples(GatherMergeState *gm_state);
      63             : static bool gather_merge_readnext(GatherMergeState *gm_state, int reader,
      64             :                                   bool nowait);
      65             : static void load_tuple_array(GatherMergeState *gm_state, int reader);
      66             : 
      67             : /* ----------------------------------------------------------------
      68             :  *      ExecInitGather
      69             :  * ----------------------------------------------------------------
      70             :  */
      71             : GatherMergeState *
      72         136 : ExecInitGatherMerge(GatherMerge *node, EState *estate, int eflags)
      73             : {
      74             :     GatherMergeState *gm_state;
      75             :     Plan       *outerNode;
      76             :     TupleDesc   tupDesc;
      77             : 
      78             :     /* Gather merge node doesn't have innerPlan node. */
      79             :     Assert(innerPlan(node) == NULL);
      80             : 
      81             :     /*
      82             :      * create state structure
      83             :      */
      84         136 :     gm_state = makeNode(GatherMergeState);
      85         136 :     gm_state->ps.plan = (Plan *) node;
      86         136 :     gm_state->ps.state = estate;
      87         136 :     gm_state->ps.ExecProcNode = ExecGatherMerge;
      88             : 
      89         136 :     gm_state->initialized = false;
      90         136 :     gm_state->gm_initialized = false;
      91         136 :     gm_state->tuples_needed = -1;
      92             : 
      93             :     /*
      94             :      * Miscellaneous initialization
      95             :      *
      96             :      * create expression context for node
      97             :      */
      98         136 :     ExecAssignExprContext(estate, &gm_state->ps);
      99             : 
     100             :     /*
     101             :      * GatherMerge doesn't support checking a qual (it's always more efficient
     102             :      * to do it in the child node).
     103             :      */
     104             :     Assert(!node->plan.qual);
     105             : 
     106             :     /*
     107             :      * now initialize outer plan
     108             :      */
     109         136 :     outerNode = outerPlan(node);
     110         136 :     outerPlanState(gm_state) = ExecInitNode(outerNode, estate, eflags);
     111             : 
     112             :     /*
     113             :      * Leader may access ExecProcNode result directly (if
     114             :      * need_to_scan_locally), or from workers via tuple queue.  So we can't
     115             :      * trivially rely on the slot type being fixed for expressions evaluated
     116             :      * within this node.
     117             :      */
     118         136 :     gm_state->ps.outeropsset = true;
     119         136 :     gm_state->ps.outeropsfixed = false;
     120             : 
     121             :     /*
     122             :      * Store the tuple descriptor into gather merge state, so we can use it
     123             :      * while initializing the gather merge slots.
     124             :      */
     125         136 :     tupDesc = ExecGetResultType(outerPlanState(gm_state));
     126         136 :     gm_state->tupDesc = tupDesc;
     127             : 
     128             :     /*
     129             :      * Initialize result type and projection.
     130             :      */
     131         136 :     ExecInitResultTypeTL(&gm_state->ps);
     132         136 :     ExecConditionalAssignProjectionInfo(&gm_state->ps, tupDesc, OUTER_VAR);
     133             : 
     134             :     /*
     135             :      * Without projections result slot type is not trivially known, see
     136             :      * comment above.
     137             :      */
     138         136 :     if (gm_state->ps.ps_ProjInfo == NULL)
     139             :     {
     140         136 :         gm_state->ps.resultopsset = true;
     141         136 :         gm_state->ps.resultopsfixed = false;
     142             :     }
     143             : 
     144             :     /*
     145             :      * initialize sort-key information
     146             :      */
     147         136 :     if (node->numCols)
     148             :     {
     149             :         int         i;
     150             : 
     151         136 :         gm_state->gm_nkeys = node->numCols;
     152         136 :         gm_state->gm_sortkeys =
     153         136 :             palloc0(sizeof(SortSupportData) * node->numCols);
     154             : 
     155         288 :         for (i = 0; i < node->numCols; i++)
     156             :         {
     157         152 :             SortSupport sortKey = gm_state->gm_sortkeys + i;
     158             : 
     159         152 :             sortKey->ssup_cxt = CurrentMemoryContext;
     160         152 :             sortKey->ssup_collation = node->collations[i];
     161         152 :             sortKey->ssup_nulls_first = node->nullsFirst[i];
     162         152 :             sortKey->ssup_attno = node->sortColIdx[i];
     163             : 
     164             :             /*
     165             :              * We don't perform abbreviated key conversion here, for the same
     166             :              * reasons that it isn't used in MergeAppend
     167             :              */
     168         152 :             sortKey->abbreviate = false;
     169             : 
     170         152 :             PrepareSortSupportFromOrderingOp(node->sortOperators[i], sortKey);
     171             :         }
     172             :     }
     173             : 
     174             :     /* Now allocate the workspace for gather merge */
     175         136 :     gather_merge_setup(gm_state);
     176             : 
     177         136 :     return gm_state;
     178             : }
     179             : 
     180             : /* ----------------------------------------------------------------
     181             :  *      ExecGatherMerge(node)
     182             :  *
     183             :  *      Scans the relation via multiple workers and returns
     184             :  *      the next qualifying tuple.
     185             :  * ----------------------------------------------------------------
     186             :  */
     187             : static TupleTableSlot *
     188      121384 : ExecGatherMerge(PlanState *pstate)
     189             : {
     190      121384 :     GatherMergeState *node = castNode(GatherMergeState, pstate);
     191             :     TupleTableSlot *slot;
     192             :     ExprContext *econtext;
     193             : 
     194      121384 :     CHECK_FOR_INTERRUPTS();
     195             : 
     196             :     /*
     197             :      * As with Gather, we don't launch workers until this node is actually
     198             :      * executed.
     199             :      */
     200      121384 :     if (!node->initialized)
     201             :     {
     202          84 :         EState     *estate = node->ps.state;
     203          84 :         GatherMerge *gm = castNode(GatherMerge, node->ps.plan);
     204             : 
     205             :         /*
     206             :          * Sometimes we might have to run without parallelism; but if parallel
     207             :          * mode is active then we can try to fire up some workers.
     208             :          */
     209          84 :         if (gm->num_workers > 0 && estate->es_use_parallel_mode)
     210             :         {
     211             :             ParallelContext *pcxt;
     212             : 
     213             :             /* Initialize, or re-initialize, shared state needed by workers. */
     214          84 :             if (!node->pei)
     215          68 :                 node->pei = ExecInitParallelPlan(node->ps.lefttree,
     216             :                                                  estate,
     217             :                                                  gm->initParam,
     218             :                                                  gm->num_workers,
     219             :                                                  node->tuples_needed);
     220             :             else
     221          32 :                 ExecParallelReinitialize(node->ps.lefttree,
     222          16 :                                          node->pei,
     223             :                                          gm->initParam);
     224             : 
     225             :             /* Try to launch workers. */
     226          84 :             pcxt = node->pei->pcxt;
     227          84 :             LaunchParallelWorkers(pcxt);
     228             :             /* We save # workers launched for the benefit of EXPLAIN */
     229          84 :             node->nworkers_launched = pcxt->nworkers_launched;
     230             : 
     231             :             /* Set up tuple queue readers to read the results. */
     232          84 :             if (pcxt->nworkers_launched > 0)
     233             :             {
     234          76 :                 ExecParallelCreateReaders(node->pei);
     235             :                 /* Make a working array showing the active readers */
     236          76 :                 node->nreaders = pcxt->nworkers_launched;
     237          76 :                 node->reader = (TupleQueueReader **)
     238          76 :                     palloc(node->nreaders * sizeof(TupleQueueReader *));
     239          76 :                 memcpy(node->reader, node->pei->reader,
     240          76 :                        node->nreaders * sizeof(TupleQueueReader *));
     241             :             }
     242             :             else
     243             :             {
     244             :                 /* No workers?  Then never mind. */
     245           8 :                 node->nreaders = 0;
     246           8 :                 node->reader = NULL;
     247             :             }
     248             :         }
     249             : 
     250             :         /* allow leader to participate if enabled or no choice */
     251          84 :         if (parallel_leader_participation || node->nreaders == 0)
     252          80 :             node->need_to_scan_locally = true;
     253          84 :         node->initialized = true;
     254             :     }
     255             : 
     256             :     /*
     257             :      * Reset per-tuple memory context to free any expression evaluation
     258             :      * storage allocated in the previous tuple cycle.
     259             :      */
     260      121384 :     econtext = node->ps.ps_ExprContext;
     261      121384 :     ResetExprContext(econtext);
     262             : 
     263             :     /*
     264             :      * Get next tuple, either from one of our workers, or by running the plan
     265             :      * ourselves.
     266             :      */
     267      121384 :     slot = gather_merge_getnext(node);
     268      121384 :     if (TupIsNull(slot))
     269          72 :         return NULL;
     270             : 
     271             :     /* If no projection is required, we're done. */
     272      121312 :     if (node->ps.ps_ProjInfo == NULL)
     273      121312 :         return slot;
     274             : 
     275             :     /*
     276             :      * Form the result tuple using ExecProject(), and return it.
     277             :      */
     278           0 :     econtext->ecxt_outertuple = slot;
     279           0 :     return ExecProject(node->ps.ps_ProjInfo);
     280             : }
     281             : 
     282             : /* ----------------------------------------------------------------
     283             :  *      ExecEndGatherMerge
     284             :  *
     285             :  *      frees any storage allocated through C routines.
     286             :  * ----------------------------------------------------------------
     287             :  */
     288             : void
     289         136 : ExecEndGatherMerge(GatherMergeState *node)
     290             : {
     291         136 :     ExecEndNode(outerPlanState(node));  /* let children clean up first */
     292         136 :     ExecShutdownGatherMerge(node);
     293         136 :     ExecFreeExprContext(&node->ps);
     294         136 :     if (node->ps.ps_ResultTupleSlot)
     295           0 :         ExecClearTuple(node->ps.ps_ResultTupleSlot);
     296         136 : }
     297             : 
     298             : /* ----------------------------------------------------------------
     299             :  *      ExecShutdownGatherMerge
     300             :  *
     301             :  *      Destroy the setup for parallel workers including parallel context.
     302             :  * ----------------------------------------------------------------
     303             :  */
     304             : void
     305         216 : ExecShutdownGatherMerge(GatherMergeState *node)
     306             : {
     307         216 :     ExecShutdownGatherMergeWorkers(node);
     308             : 
     309             :     /* Now destroy the parallel context. */
     310         216 :     if (node->pei != NULL)
     311             :     {
     312          68 :         ExecParallelCleanup(node->pei);
     313          68 :         node->pei = NULL;
     314             :     }
     315         216 : }
     316             : 
     317             : /* ----------------------------------------------------------------
     318             :  *      ExecShutdownGatherMergeWorkers
     319             :  *
     320             :  *      Stop all the parallel workers.
     321             :  * ----------------------------------------------------------------
     322             :  */
     323             : static void
     324         240 : ExecShutdownGatherMergeWorkers(GatherMergeState *node)
     325             : {
     326         240 :     if (node->pei != NULL)
     327          84 :         ExecParallelFinish(node->pei);
     328             : 
     329             :     /* Flush local copy of reader array */
     330         240 :     if (node->reader)
     331          76 :         pfree(node->reader);
     332         240 :     node->reader = NULL;
     333         240 : }
     334             : 
     335             : /* ----------------------------------------------------------------
     336             :  *      ExecReScanGatherMerge
     337             :  *
     338             :  *      Prepare to re-scan the result of a GatherMerge.
     339             :  * ----------------------------------------------------------------
     340             :  */
     341             : void
     342          24 : ExecReScanGatherMerge(GatherMergeState *node)
     343             : {
     344          24 :     GatherMerge *gm = (GatherMerge *) node->ps.plan;
     345          24 :     PlanState  *outerPlan = outerPlanState(node);
     346             : 
     347             :     /* Make sure any existing workers are gracefully shut down */
     348          24 :     ExecShutdownGatherMergeWorkers(node);
     349             : 
     350             :     /* Free any unused tuples, so we don't leak memory across rescans */
     351          24 :     gather_merge_clear_tuples(node);
     352             : 
     353             :     /* Mark node so that shared state will be rebuilt at next call */
     354          24 :     node->initialized = false;
     355          24 :     node->gm_initialized = false;
     356             : 
     357             :     /*
     358             :      * Set child node's chgParam to tell it that the next scan might deliver a
     359             :      * different set of rows within the leader process.  (The overall rowset
     360             :      * shouldn't change, but the leader process's subset might; hence nodes
     361             :      * between here and the parallel table scan node mustn't optimize on the
     362             :      * assumption of an unchanging rowset.)
     363             :      */
     364          24 :     if (gm->rescan_param >= 0)
     365          24 :         outerPlan->chgParam = bms_add_member(outerPlan->chgParam,
     366             :                                              gm->rescan_param);
     367             : 
     368             :     /*
     369             :      * If chgParam of subnode is not null then plan will be re-scanned by
     370             :      * first ExecProcNode.  Note: because this does nothing if we have a
     371             :      * rescan_param, it's currently guaranteed that parallel-aware child nodes
     372             :      * will not see a ReScan call until after they get a ReInitializeDSM call.
     373             :      * That ordering might not be something to rely on, though.  A good rule
     374             :      * of thumb is that ReInitializeDSM should reset only shared state, ReScan
     375             :      * should reset only local state, and anything that depends on both of
     376             :      * those steps being finished must wait until the first ExecProcNode call.
     377             :      */
     378          24 :     if (outerPlan->chgParam == NULL)
     379           0 :         ExecReScan(outerPlan);
     380          24 : }
     381             : 
     382             : /*
     383             :  * Set up the data structures that we'll need for Gather Merge.
     384             :  *
     385             :  * We allocate these once on the basis of gm->num_workers, which is an
     386             :  * upper bound for the number of workers we'll actually have.  During
     387             :  * a rescan, we reset the structures to empty.  This approach simplifies
     388             :  * not leaking memory across rescans.
     389             :  *
     390             :  * In the gm_slots[] array, index 0 is for the leader, and indexes 1 to n
     391             :  * are for workers.  The values placed into gm_heap correspond to indexes
     392             :  * in gm_slots[].  The gm_tuple_buffers[] array, however, is indexed from
     393             :  * 0 to n-1; it has no entry for the leader.
     394             :  */
     395             : static void
     396         136 : gather_merge_setup(GatherMergeState *gm_state)
     397             : {
     398         136 :     GatherMerge *gm = castNode(GatherMerge, gm_state->ps.plan);
     399         136 :     int         nreaders = gm->num_workers;
     400             :     int         i;
     401             : 
     402             :     /*
     403             :      * Allocate gm_slots for the number of workers + one more slot for leader.
     404             :      * Slot 0 is always for the leader.  Leader always calls ExecProcNode() to
     405             :      * read the tuple, and then stores it directly into its gm_slots entry.
     406             :      * For other slots, code below will call ExecInitExtraTupleSlot() to
     407             :      * create a slot for the worker's results.  Note that during any single
     408             :      * scan, we might have fewer than num_workers available workers, in which
     409             :      * case the extra array entries go unused.
     410             :      */
     411         136 :     gm_state->gm_slots = (TupleTableSlot **)
     412         136 :         palloc0((nreaders + 1) * sizeof(TupleTableSlot *));
     413             : 
     414             :     /* Allocate the tuple slot and tuple array for each worker */
     415         136 :     gm_state->gm_tuple_buffers = (GMReaderTupleBuffer *)
     416         136 :         palloc0(nreaders * sizeof(GMReaderTupleBuffer));
     417             : 
     418         536 :     for (i = 0; i < nreaders; i++)
     419             :     {
     420             :         /* Allocate the tuple array with length MAX_TUPLE_STORE */
     421         800 :         gm_state->gm_tuple_buffers[i].tuple =
     422         400 :             (HeapTuple *) palloc0(sizeof(HeapTuple) * MAX_TUPLE_STORE);
     423             : 
     424             :         /* Initialize tuple slot for worker */
     425         800 :         gm_state->gm_slots[i + 1] =
     426         400 :             ExecInitExtraTupleSlot(gm_state->ps.state, gm_state->tupDesc,
     427             :                                    &TTSOpsHeapTuple);
     428             :     }
     429             : 
     430             :     /* Allocate the resources for the merge */
     431         136 :     gm_state->gm_heap = binaryheap_allocate(nreaders + 1,
     432             :                                             heap_compare_slots,
     433             :                                             gm_state);
     434         136 : }
     435             : 
     436             : /*
     437             :  * Initialize the Gather Merge.
     438             :  *
     439             :  * Reset data structures to ensure they're empty.  Then pull at least one
     440             :  * tuple from leader + each worker (or set its "done" indicator), and set up
     441             :  * the heap.
     442             :  */
     443             : static void
     444          84 : gather_merge_init(GatherMergeState *gm_state)
     445             : {
     446          84 :     int         nreaders = gm_state->nreaders;
     447          84 :     bool        nowait = true;
     448             :     int         i;
     449             : 
     450             :     /* Assert that gather_merge_setup made enough space */
     451             :     Assert(nreaders <= castNode(GatherMerge, gm_state->ps.plan)->num_workers);
     452             : 
     453             :     /* Reset leader's tuple slot to empty */
     454          84 :     gm_state->gm_slots[0] = NULL;
     455             : 
     456             :     /* Reset the tuple slot and tuple array for each worker */
     457         316 :     for (i = 0; i < nreaders; i++)
     458             :     {
     459             :         /* Reset tuple array to empty */
     460         232 :         gm_state->gm_tuple_buffers[i].nTuples = 0;
     461         232 :         gm_state->gm_tuple_buffers[i].readCounter = 0;
     462             :         /* Reset done flag to not-done */
     463         232 :         gm_state->gm_tuple_buffers[i].done = false;
     464             :         /* Ensure output slot is empty */
     465         232 :         ExecClearTuple(gm_state->gm_slots[i + 1]);
     466             :     }
     467             : 
     468             :     /* Reset binary heap to empty */
     469          84 :     binaryheap_reset(gm_state->gm_heap);
     470             : 
     471             :     /*
     472             :      * First, try to read a tuple from each worker (including leader) in
     473             :      * nowait mode.  After this, if not all workers were able to produce a
     474             :      * tuple (or a "done" indication), then re-read from remaining workers,
     475             :      * this time using wait mode.  Add all live readers (those producing at
     476             :      * least one tuple) to the heap.
     477             :      */
     478             : reread:
     479         784 :     for (i = 0; i <= nreaders; i++)
     480             :     {
     481         624 :         CHECK_FOR_INTERRUPTS();
     482             : 
     483             :         /* skip this source if already known done */
     484        1088 :         if ((i == 0) ? gm_state->need_to_scan_locally :
     485         464 :             !gm_state->gm_tuple_buffers[i - 1].done)
     486             :         {
     487         614 :             if (TupIsNull(gm_state->gm_slots[i]))
     488             :             {
     489             :                 /* Don't have a tuple yet, try to get one */
     490        1084 :                 if (gather_merge_readnext(gm_state, i, nowait))
     491          86 :                     binaryheap_add_unordered(gm_state->gm_heap,
     492             :                                              Int32GetDatum(i));
     493             :             }
     494             :             else
     495             :             {
     496             :                 /*
     497             :                  * We already got at least one tuple from this worker, but
     498             :                  * might as well see if it has any more ready by now.
     499             :                  */
     500          72 :                 load_tuple_array(gm_state, i);
     501             :             }
     502             :         }
     503             :     }
     504             : 
     505             :     /* need not recheck leader, since nowait doesn't matter for it */
     506         392 :     for (i = 1; i <= nreaders; i++)
     507             :     {
     508         388 :         if (!gm_state->gm_tuple_buffers[i - 1].done &&
     509         160 :             TupIsNull(gm_state->gm_slots[i]))
     510             :         {
     511          76 :             nowait = false;
     512          76 :             goto reread;
     513             :         }
     514             :     }
     515             : 
     516             :     /* Now heapify the heap. */
     517          84 :     binaryheap_build(gm_state->gm_heap);
     518             : 
     519          84 :     gm_state->gm_initialized = true;
     520          84 : }
     521             : 
     522             : /*
     523             :  * Clear out the tuple table slot, and any unused pending tuples,
     524             :  * for each gather merge input.
     525             :  */
     526             : static void
     527          96 : gather_merge_clear_tuples(GatherMergeState *gm_state)
     528             : {
     529             :     int         i;
     530             : 
     531         376 :     for (i = 0; i < gm_state->nreaders; i++)
     532             :     {
     533         280 :         GMReaderTupleBuffer *tuple_buffer = &gm_state->gm_tuple_buffers[i];
     534             : 
     535         560 :         while (tuple_buffer->readCounter < tuple_buffer->nTuples)
     536           0 :             heap_freetuple(tuple_buffer->tuple[tuple_buffer->readCounter++]);
     537             : 
     538         280 :         ExecClearTuple(gm_state->gm_slots[i + 1]);
     539             :     }
     540          96 : }
     541             : 
     542             : /*
     543             :  * Read the next tuple for gather merge.
     544             :  *
     545             :  * Fetch the sorted tuple out of the heap.
     546             :  */
     547             : static TupleTableSlot *
     548      121384 : gather_merge_getnext(GatherMergeState *gm_state)
     549             : {
     550             :     int         i;
     551             : 
     552      121384 :     if (!gm_state->gm_initialized)
     553             :     {
     554             :         /*
     555             :          * First time through: pull the first tuple from each participant, and
     556             :          * set up the heap.
     557             :          */
     558          84 :         gather_merge_init(gm_state);
     559             :     }
     560             :     else
     561             :     {
     562             :         /*
     563             :          * Otherwise, pull the next tuple from whichever participant we
     564             :          * returned from last time, and reinsert that participant's index into
     565             :          * the heap, because it might now compare differently against the
     566             :          * other elements of the heap.
     567             :          */
     568      121300 :         i = DatumGetInt32(binaryheap_first(gm_state->gm_heap));
     569             : 
     570      121300 :         if (gather_merge_readnext(gm_state, i, false))
     571      121226 :             binaryheap_replace_first(gm_state->gm_heap, Int32GetDatum(i));
     572             :         else
     573             :         {
     574             :             /* reader exhausted, remove it from heap */
     575          74 :             (void) binaryheap_remove_first(gm_state->gm_heap);
     576             :         }
     577             :     }
     578             : 
     579      121384 :     if (binaryheap_empty(gm_state->gm_heap))
     580             :     {
     581             :         /* All the queues are exhausted, and so is the heap */
     582          72 :         gather_merge_clear_tuples(gm_state);
     583          72 :         return NULL;
     584             :     }
     585             :     else
     586             :     {
     587             :         /* Return next tuple from whichever participant has the leading one */
     588      121312 :         i = DatumGetInt32(binaryheap_first(gm_state->gm_heap));
     589      121312 :         return gm_state->gm_slots[i];
     590             :     }
     591             : }
     592             : 
     593             : /*
     594             :  * Read tuple(s) for given reader in nowait mode, and load into its tuple
     595             :  * array, until we have MAX_TUPLE_STORE of them or would have to block.
     596             :  */
     597             : static void
     598          82 : load_tuple_array(GatherMergeState *gm_state, int reader)
     599             : {
     600             :     GMReaderTupleBuffer *tuple_buffer;
     601             :     int         i;
     602             : 
     603             :     /* Don't do anything if this is the leader. */
     604          82 :     if (reader == 0)
     605          72 :         return;
     606             : 
     607          10 :     tuple_buffer = &gm_state->gm_tuple_buffers[reader - 1];
     608             : 
     609             :     /* If there's nothing in the array, reset the counters to zero. */
     610          10 :     if (tuple_buffer->nTuples == tuple_buffer->readCounter)
     611          10 :         tuple_buffer->nTuples = tuple_buffer->readCounter = 0;
     612             : 
     613             :     /* Try to fill additional slots in the array. */
     614         100 :     for (i = tuple_buffer->nTuples; i < MAX_TUPLE_STORE; i++)
     615             :     {
     616             :         HeapTuple   tuple;
     617             : 
     618          96 :         tuple = gm_readnext_tuple(gm_state,
     619             :                                   reader,
     620             :                                   true,
     621             :                                   &tuple_buffer->done);
     622          96 :         if (!HeapTupleIsValid(tuple))
     623           6 :             break;
     624          90 :         tuple_buffer->tuple[i] = tuple;
     625          90 :         tuple_buffer->nTuples++;
     626             :     }
     627             : }
     628             : 
     629             : /*
     630             :  * Store the next tuple for a given reader into the appropriate slot.
     631             :  *
     632             :  * Returns true if successful, false if not (either reader is exhausted,
     633             :  * or we didn't want to wait for a tuple).  Sets done flag if reader
     634             :  * is found to be exhausted.
     635             :  */
     636             : static bool
     637      121842 : gather_merge_readnext(GatherMergeState *gm_state, int reader, bool nowait)
     638             : {
     639             :     GMReaderTupleBuffer *tuple_buffer;
     640             :     HeapTuple   tup;
     641             : 
     642             :     /*
     643             :      * If we're being asked to generate a tuple from the leader, then we just
     644             :      * call ExecProcNode as normal to produce one.
     645             :      */
     646      121842 :     if (reader == 0)
     647             :     {
     648      121280 :         if (gm_state->need_to_scan_locally)
     649             :         {
     650      121280 :             PlanState  *outerPlan = outerPlanState(gm_state);
     651             :             TupleTableSlot *outerTupleSlot;
     652      121280 :             EState     *estate = gm_state->ps.state;
     653             : 
     654             :             /* Install our DSA area while executing the plan. */
     655      121280 :             estate->es_query_dsa = gm_state->pei ? gm_state->pei->area : NULL;
     656      121280 :             outerTupleSlot = ExecProcNode(outerPlan);
     657      121280 :             estate->es_query_dsa = NULL;
     658             : 
     659      121280 :             if (!TupIsNull(outerTupleSlot))
     660             :             {
     661      121212 :                 gm_state->gm_slots[0] = outerTupleSlot;
     662      121212 :                 return true;
     663             :             }
     664             :             /* need_to_scan_locally serves as "done" flag for leader */
     665          68 :             gm_state->need_to_scan_locally = false;
     666             :         }
     667          68 :         return false;
     668             :     }
     669             : 
     670             :     /* Otherwise, check the state of the relevant tuple buffer. */
     671         562 :     tuple_buffer = &gm_state->gm_tuple_buffers[reader - 1];
     672             : 
     673         562 :     if (tuple_buffer->nTuples > tuple_buffer->readCounter)
     674             :     {
     675             :         /* Return any tuple previously read that is still buffered. */
     676          90 :         tup = tuple_buffer->tuple[tuple_buffer->readCounter++];
     677             :     }
     678         472 :     else if (tuple_buffer->done)
     679             :     {
     680             :         /* Reader is known to be exhausted. */
     681           6 :         return false;
     682             :     }
     683             :     else
     684             :     {
     685             :         /* Read and buffer next tuple. */
     686         466 :         tup = gm_readnext_tuple(gm_state,
     687             :                                 reader,
     688             :                                 nowait,
     689             :                                 &tuple_buffer->done);
     690         466 :         if (!HeapTupleIsValid(tup))
     691         456 :             return false;
     692             : 
     693             :         /*
     694             :          * Attempt to read more tuples in nowait mode and store them in the
     695             :          * pending-tuple array for the reader.
     696             :          */
     697          10 :         load_tuple_array(gm_state, reader);
     698             :     }
     699             : 
     700             :     Assert(HeapTupleIsValid(tup));
     701             : 
     702             :     /* Build the TupleTableSlot for the given tuple */
     703         100 :     ExecStoreHeapTuple(tup,     /* tuple to store */
     704         100 :                        gm_state->gm_slots[reader],   /* slot in which to store
     705             :                                                      * the tuple */
     706             :                        true);   /* pfree tuple when done with it */
     707             : 
     708         100 :     return true;
     709             : }
     710             : 
     711             : /*
     712             :  * Attempt to read a tuple from given worker.
     713             :  */
     714             : static HeapTuple
     715         562 : gm_readnext_tuple(GatherMergeState *gm_state, int nreader, bool nowait,
     716             :                   bool *done)
     717             : {
     718             :     TupleQueueReader *reader;
     719             :     HeapTuple   tup;
     720             : 
     721             :     /* Check for async events, particularly messages from workers. */
     722         562 :     CHECK_FOR_INTERRUPTS();
     723             : 
     724             :     /*
     725             :      * Attempt to read a tuple.
     726             :      *
     727             :      * Note that TupleQueueReaderNext will just return NULL for a worker which
     728             :      * fails to initialize.  We'll treat that worker as having produced no
     729             :      * tuples; WaitForParallelWorkersToFinish will error out when we get
     730             :      * there.
     731             :      */
     732         562 :     reader = gm_state->reader[nreader - 1];
     733         562 :     tup = TupleQueueReaderNext(reader, nowait, done);
     734             : 
     735         562 :     return tup;
     736             : }
     737             : 
     738             : /*
     739             :  * We have one slot for each item in the heap array.  We use SlotNumber
     740             :  * to store slot indexes.  This doesn't actually provide any formal
     741             :  * type-safety, but it makes the code more self-documenting.
     742             :  */
     743             : typedef int32 SlotNumber;
     744             : 
     745             : /*
     746             :  * Compare the tuples in the two given slots.
     747             :  */
     748             : static int32
     749          20 : heap_compare_slots(Datum a, Datum b, void *arg)
     750             : {
     751          20 :     GatherMergeState *node = (GatherMergeState *) arg;
     752          20 :     SlotNumber  slot1 = DatumGetInt32(a);
     753          20 :     SlotNumber  slot2 = DatumGetInt32(b);
     754             : 
     755          20 :     TupleTableSlot *s1 = node->gm_slots[slot1];
     756          20 :     TupleTableSlot *s2 = node->gm_slots[slot2];
     757             :     int         nkey;
     758             : 
     759             :     Assert(!TupIsNull(s1));
     760             :     Assert(!TupIsNull(s2));
     761             : 
     762          20 :     for (nkey = 0; nkey < node->gm_nkeys; nkey++)
     763             :     {
     764          20 :         SortSupport sortKey = node->gm_sortkeys + nkey;
     765          20 :         AttrNumber  attno = sortKey->ssup_attno;
     766             :         Datum       datum1,
     767             :                     datum2;
     768             :         bool        isNull1,
     769             :                     isNull2;
     770             :         int         compare;
     771             : 
     772          20 :         datum1 = slot_getattr(s1, attno, &isNull1);
     773          20 :         datum2 = slot_getattr(s2, attno, &isNull2);
     774             : 
     775          20 :         compare = ApplySortComparator(datum1, isNull1,
     776             :                                       datum2, isNull2,
     777             :                                       sortKey);
     778          20 :         if (compare != 0)
     779             :         {
     780          20 :             INVERT_COMPARE_RESULT(compare);
     781          20 :             return compare;
     782             :         }
     783             :     }
     784           0 :     return 0;
     785             : }

Generated by: LCOV version 1.13