/src/postgres/src/backend/executor/execParallel.c

Source
/*-------------------------------------------------------------------------
 *
 * execParallel.c
 *    Support routines for parallel execution.
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * This file contains routines that are intended to support setting up,
 * using, and tearing down a ParallelContext from within the PostgreSQL
 * executor.  The ParallelContext machinery will handle starting the
 * workers and ensuring that their state generally matches that of the
 * leader; see src/backend/access/transam/README.parallel for details.
 * However, we must save and restore relevant executor state, such as
 * any ParamListInfo associated with the query, buffer/WAL usage info, and
 * the actual plan to be passed down to the worker.
 *
 * IDENTIFICATION
 *    src/backend/executor/execParallel.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "executor/execParallel.h"
#include "executor/executor.h"
#include "executor/nodeAgg.h"
#include "executor/nodeAppend.h"
#include "executor/nodeBitmapHeapscan.h"
#include "executor/nodeBitmapIndexscan.h"
#include "executor/nodeCustom.h"
#include "executor/nodeForeignscan.h"
#include "executor/nodeHash.h"
#include "executor/nodeHashjoin.h"
#include "executor/nodeIncrementalSort.h"
#include "executor/nodeIndexonlyscan.h"
#include "executor/nodeIndexscan.h"
#include "executor/nodeMaterial.h"
#include "executor/nodeMemoize.h"
#include "executor/nodeSeqscan.h"
#include "executor/nodeSort.h"
#include "executor/nodeSubplan.h"
#include "executor/nodeTidrangescan.h"
#include "executor/tqueue.h"
#include "jit/jit.h"
#include "nodes/nodeFuncs.h"
#include "pgstat.h"
#include "storage/proc.h"
#include "tcop/tcopprot.h"
#include "utils/datum.h"
#include "utils/dsa.h"
#include "utils/lsyscache.h"
#include "utils/snapmgr.h"

/*
 * Magic numbers for parallel executor communication.  We use constants
 * greater than any 32-bit integer here so that values < 2^32 can be used
 * by individual parallel nodes to store their own state.
 */
#define PARALLEL_KEY_EXECUTOR_FIXED   UINT64CONST(0xE000000000000001)
#define PARALLEL_KEY_PLANNEDSTMT    UINT64CONST(0xE000000000000002)
#define PARALLEL_KEY_PARAMLISTINFO    UINT64CONST(0xE000000000000003)
#define PARALLEL_KEY_BUFFER_USAGE   UINT64CONST(0xE000000000000004)
#define PARALLEL_KEY_TUPLE_QUEUE    UINT64CONST(0xE000000000000005)
#define PARALLEL_KEY_INSTRUMENTATION  UINT64CONST(0xE000000000000006)
#define PARALLEL_KEY_DSA        UINT64CONST(0xE000000000000007)
#define PARALLEL_KEY_QUERY_TEXT   UINT64CONST(0xE000000000000008)
#define PARALLEL_KEY_JIT_INSTRUMENTATION UINT64CONST(0xE000000000000009)
#define PARALLEL_KEY_WAL_USAGE      UINT64CONST(0xE00000000000000A)

#define PARALLEL_TUPLE_QUEUE_SIZE   65536

/*
 * Fixed-size random stuff that we need to pass to parallel workers.
 */
typedef struct FixedParallelExecutorState
{
  int64   tuples_needed;  /* tuple bound, see ExecSetTupleBound */
  dsa_pointer param_exec;
  int     eflags;
  int     jit_flags;
} FixedParallelExecutorState;

/*
 * DSM structure for accumulating per-PlanState instrumentation.
 *
 * instrument_options: Same meaning here as in instrument.c.
 *
 * instrument_offset: Offset, relative to the start of this structure,
 * of the first NodeInstrumentation object.  This will depend on the length of
 * the plan_node_id array.
 *
 * num_workers: Number of workers.
 *
 * num_plan_nodes: Number of plan nodes.
 *
 * plan_node_id: Array of plan nodes for which we are gathering instrumentation
 * from parallel workers.  The length of this array is given by num_plan_nodes.
 */
struct SharedExecutorInstrumentation
{
  int     instrument_options;
  int     instrument_offset;
  int     num_workers;
  int     num_plan_nodes;
  int     plan_node_id[FLEXIBLE_ARRAY_MEMBER];

  /*
   * Array of num_plan_nodes * num_workers NodeInstrumentation objects
   * follows.
   */
};
#define GetInstrumentationArray(sei) \
  (StaticAssertVariableIsOfTypeMacro(sei, SharedExecutorInstrumentation *), \
   (NodeInstrumentation *) (((char *) sei) + sei->instrument_offset))

/* Context object for ExecParallelEstimate. */
typedef struct ExecParallelEstimateContext
{
  ParallelContext *pcxt;
  int     nnodes;
} ExecParallelEstimateContext;

/* Context object for ExecParallelInitializeDSM. */
typedef struct ExecParallelInitializeDSMContext
{
  ParallelContext *pcxt;
  SharedExecutorInstrumentation *instrumentation;
  int     nnodes;
} ExecParallelInitializeDSMContext;

/* Helper functions that run in the parallel leader. */
static char *ExecSerializePlan(Plan *plan, EState *estate);
static bool ExecParallelEstimate(PlanState *planstate,
                 ExecParallelEstimateContext *e);
static bool ExecParallelInitializeDSM(PlanState *planstate,
                    ExecParallelInitializeDSMContext *d);
static shm_mq_handle **ExecParallelSetupTupleQueues(ParallelContext *pcxt,
                          bool reinitialize);
static bool ExecParallelReInitializeDSM(PlanState *planstate,
                    ParallelContext *pcxt);
static bool ExecParallelRetrieveInstrumentation(PlanState *planstate,
                        SharedExecutorInstrumentation *instrumentation);

/* Helper function that runs in the parallel worker. */
static DestReceiver *ExecParallelGetReceiver(dsm_segment *seg, shm_toc *toc);

/*
 * Create a serialized representation of the plan to be sent to each worker.
 */
static char *
ExecSerializePlan(Plan *plan, EState *estate)
{
  PlannedStmt *pstmt;
  ListCell   *lc;

  /* We can't scribble on the original plan, so make a copy. */
  plan = copyObject(plan);

  /*
   * The worker will start its own copy of the executor, and that copy will
   * insert a junk filter if the toplevel node has any resjunk entries. We
   * don't want that to happen, because while resjunk columns shouldn't be
   * sent back to the user, here the tuples are coming back to another
   * backend which may very well need them.  So mutate the target list
   * accordingly.  This is sort of a hack; there might be better ways to do
   * this...
   */
  foreach(lc, plan->targetlist)
  {
    TargetEntry *tle = lfirst_node(TargetEntry, lc);

    tle->resjunk = false;
  }

  /*
   * Create a dummy PlannedStmt.  Most of the fields don't need to be valid
   * for our purposes, but the worker will need at least a minimal
   * PlannedStmt to start the executor.
   */
  pstmt = makeNode(PlannedStmt);
  pstmt->commandType = CMD_SELECT;
  pstmt->queryId = pgstat_get_my_query_id();
  pstmt->planId = pgstat_get_my_plan_id();
  pstmt->hasReturning = false;
  pstmt->hasModifyingCTE = false;
  pstmt->canSetTag = true;
  pstmt->transientPlan = false;
  pstmt->dependsOnRole = false;
  pstmt->parallelModeNeeded = false;
  pstmt->planTree = plan;
  pstmt->partPruneInfos = estate->es_part_prune_infos;
  pstmt->rtable = estate->es_range_table;
  pstmt->unprunableRelids = estate->es_unpruned_relids;
  pstmt->permInfos = estate->es_rteperminfos;
  pstmt->appendRelations = NIL;
  pstmt->planOrigin = PLAN_STMT_INTERNAL;

  /*
   * Transfer only parallel-safe subplans, leaving a NULL "hole" in the list
   * for unsafe ones (so that the list indexes of the safe ones are
   * preserved).  This positively ensures that the worker won't try to run,
   * or even do ExecInitNode on, an unsafe subplan.  That's important to
   * protect, eg, non-parallel-aware FDWs from getting into trouble.
   */
  pstmt->subplans = NIL;
  foreach(lc, estate->es_plannedstmt->subplans)
  {
    Plan     *subplan = (Plan *) lfirst(lc);

    if (subplan && !subplan->parallel_safe)
      subplan = NULL;
    pstmt->subplans = lappend(pstmt->subplans, subplan);
  }

  pstmt->rewindPlanIDs = NULL;
  pstmt->rowMarks = NIL;

  /*
   * Pass the row mark and result relation relids to parallel workers. They
   * may need to check them to inform heuristics.
   */
  pstmt->rowMarkRelids = estate->es_plannedstmt->rowMarkRelids;
  pstmt->resultRelationRelids = estate->es_plannedstmt->resultRelationRelids;
  pstmt->relationOids = NIL;
  pstmt->invalItems = NIL; /* workers can't replan anyway... */
  pstmt->paramExecTypes = estate->es_plannedstmt->paramExecTypes;
  pstmt->utilityStmt = NULL;
  pstmt->stmt_location = -1;
  pstmt->stmt_len = -1;

  /* Return serialized copy of our dummy PlannedStmt. */
  return nodeToString(pstmt);
}

/*
 * Parallel-aware plan nodes (and occasionally others) may need some state
 * which is shared across all parallel workers.  Before we size the DSM, give
 * them a chance to call shm_toc_estimate_chunk or shm_toc_estimate_keys on
 * &pcxt->estimator.
 *
 * While we're at it, count the number of PlanState nodes in the tree, so
 * we know how many Instrumentation structures we need.
 */
static bool
ExecParallelEstimate(PlanState *planstate, ExecParallelEstimateContext *e)
{
  if (planstate == NULL)
    return false;

  /* Count this node. */
  e->nnodes++;

  switch (nodeTag(planstate))
  {
    case T_SeqScanState:
      if (planstate->plan->parallel_aware)
        ExecSeqScanEstimate((SeqScanState *) planstate,
                  e->pcxt);
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecSeqScanInstrumentEstimate((SeqScanState *) planstate,
                      e->pcxt);
      break;
    case T_IndexScanState:
      if (planstate->plan->parallel_aware)
        ExecIndexScanEstimate((IndexScanState *) planstate,
                    e->pcxt);
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecIndexScanInstrumentEstimate((IndexScanState *) planstate,
                      e->pcxt);
      break;
    case T_IndexOnlyScanState:
      if (planstate->plan->parallel_aware)
        ExecIndexOnlyScanEstimate((IndexOnlyScanState *) planstate,
                      e->pcxt);
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecIndexOnlyScanInstrumentEstimate((IndexOnlyScanState *) planstate,
                        e->pcxt);
      break;
    case T_BitmapIndexScanState:
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecBitmapIndexScanEstimate((BitmapIndexScanState *) planstate,
                    e->pcxt);
      break;
    case T_ForeignScanState:
      if (planstate->plan->parallel_aware)
        ExecForeignScanEstimate((ForeignScanState *) planstate,
                    e->pcxt);
      break;
    case T_TidRangeScanState:
      if (planstate->plan->parallel_aware)
        ExecTidRangeScanEstimate((TidRangeScanState *) planstate,
                     e->pcxt);
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecTidRangeScanInstrumentEstimate((TidRangeScanState *) planstate,
                         e->pcxt);
      break;
    case T_AppendState:
      if (planstate->plan->parallel_aware)
        ExecAppendEstimate((AppendState *) planstate,
                   e->pcxt);
      break;
    case T_CustomScanState:
      if (planstate->plan->parallel_aware)
        ExecCustomScanEstimate((CustomScanState *) planstate,
                     e->pcxt);
      break;
    case T_BitmapHeapScanState:
      if (planstate->plan->parallel_aware)
        ExecBitmapHeapEstimate((BitmapHeapScanState *) planstate,
                     e->pcxt);
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecBitmapHeapInstrumentEstimate((BitmapHeapScanState *) planstate,
                       e->pcxt);
      break;
    case T_HashJoinState:
      if (planstate->plan->parallel_aware)
        ExecHashJoinEstimate((HashJoinState *) planstate,
                   e->pcxt);
      break;
    case T_HashState:
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecHashEstimate((HashState *) planstate, e->pcxt);
      break;
    case T_SortState:
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecSortEstimate((SortState *) planstate, e->pcxt);
      break;
    case T_IncrementalSortState:
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecIncrementalSortEstimate((IncrementalSortState *) planstate, e->pcxt);
      break;
    case T_AggState:
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecAggEstimate((AggState *) planstate, e->pcxt);
      break;
    case T_MemoizeState:
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecMemoizeEstimate((MemoizeState *) planstate, e->pcxt);
      break;
    case T_MaterialState:
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecMaterialEstimate((MaterialState *) planstate, e->pcxt);
      break;
    default:
      break;
  }

  return planstate_tree_walker(planstate, ExecParallelEstimate, e);
}

/*
 * Estimate the amount of space required to serialize the indicated parameters.
 */
static Size
EstimateParamExecSpace(EState *estate, Bitmapset *params)
{
  int     paramid;
  Size    sz = sizeof(int);

  paramid = -1;
  while ((paramid = bms_next_member(params, paramid)) >= 0)
  {
    Oid     typeOid;
    int16   typLen;
    bool    typByVal;
    ParamExecData *prm;

    prm = &(estate->es_param_exec_vals[paramid]);
    typeOid = list_nth_oid(estate->es_plannedstmt->paramExecTypes,
                 paramid);

    sz = add_size(sz, sizeof(int)); /* space for paramid */

    /* space for datum/isnull */
    if (OidIsValid(typeOid))
      get_typlenbyval(typeOid, &typLen, &typByVal);
    else
    {
      /* If no type OID, assume by-value, like copyParamList does. */
      typLen = sizeof(Datum);
      typByVal = true;
    }
    sz = add_size(sz,
            datumEstimateSpace(prm->value, prm->isnull,
                     typByVal, typLen));
  }
  return sz;
}

/*
 * Serialize specified PARAM_EXEC parameters.
 *
 * We write the number of parameters first, as a 4-byte integer, and then
 * write details for each parameter in turn.  The details for each parameter
 * consist of a 4-byte paramid (location of param in execution time internal
 * parameter array) and then the datum as serialized by datumSerialize().
 */
static dsa_pointer
SerializeParamExecParams(EState *estate, Bitmapset *params, dsa_area *area)
{
  Size    size;
  int     nparams;
  int     paramid;
  ParamExecData *prm;
  dsa_pointer handle;
  char     *start_address;

  /* Allocate enough space for the current parameter values. */
  size = EstimateParamExecSpace(estate, params);
  handle = dsa_allocate(area, size);
  start_address = dsa_get_address(area, handle);

  /* First write the number of parameters as a 4-byte integer. */
  nparams = bms_num_members(params);
  memcpy(start_address, &nparams, sizeof(int));
  start_address += sizeof(int);

  /* Write details for each parameter in turn. */
  paramid = -1;
  while ((paramid = bms_next_member(params, paramid)) >= 0)
  {
    Oid     typeOid;
    int16   typLen;
    bool    typByVal;

    prm = &(estate->es_param_exec_vals[paramid]);
    typeOid = list_nth_oid(estate->es_plannedstmt->paramExecTypes,
                 paramid);

    /* Write paramid. */
    memcpy(start_address, &paramid, sizeof(int));
    start_address += sizeof(int);

    /* Write datum/isnull */
    if (OidIsValid(typeOid))
      get_typlenbyval(typeOid, &typLen, &typByVal);
    else
    {
      /* If no type OID, assume by-value, like copyParamList does. */
      typLen = sizeof(Datum);
      typByVal = true;
    }
    datumSerialize(prm->value, prm->isnull, typByVal, typLen,
             &start_address);
  }

  return handle;
}

/*
 * Restore specified PARAM_EXEC parameters.
 */
static void
RestoreParamExecParams(char *start_address, EState *estate)
{
  int     nparams;
  int     i;
  int     paramid;

  memcpy(&nparams, start_address, sizeof(int));
  start_address += sizeof(int);

  for (i = 0; i < nparams; i++)
  {
    ParamExecData *prm;

    /* Read paramid */
    memcpy(&paramid, start_address, sizeof(int));
    start_address += sizeof(int);
    prm = &(estate->es_param_exec_vals[paramid]);

    /* Read datum/isnull. */
    prm->value = datumRestore(&start_address, &prm->isnull);
    prm->execPlan = NULL;
  }
}

/*
 * Initialize the dynamic shared memory segment that will be used to control
 * parallel execution.
 */
static bool
ExecParallelInitializeDSM(PlanState *planstate,
              ExecParallelInitializeDSMContext *d)
{
  if (planstate == NULL)
    return false;

  /* If instrumentation is enabled, initialize slot for this node. */
  if (d->instrumentation != NULL)
    d->instrumentation->plan_node_id[d->nnodes] =
      planstate->plan->plan_node_id;

  /* Count this node. */
  d->nnodes++;

  /*
   * Call initializers for DSM-using plan nodes.
   *
   * Most plan nodes won't do anything here, but plan nodes that allocated
   * DSM may need to initialize shared state in the DSM before parallel
   * workers are launched.  They can allocate the space they previously
   * estimated using shm_toc_allocate, and add the keys they previously
   * estimated using shm_toc_insert, in each case targeting pcxt->toc.
   */
  switch (nodeTag(planstate))
  {
    case T_SeqScanState:
      if (planstate->plan->parallel_aware)
        ExecSeqScanInitializeDSM((SeqScanState *) planstate,
                     d->pcxt);
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecSeqScanInstrumentInitDSM((SeqScanState *) planstate,
                     d->pcxt);
      break;
    case T_IndexScanState:
      if (planstate->plan->parallel_aware)
        ExecIndexScanInitializeDSM((IndexScanState *) planstate,
                       d->pcxt);
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecIndexScanInstrumentInitDSM((IndexScanState *) planstate,
                       d->pcxt);
      break;
    case T_IndexOnlyScanState:
      if (planstate->plan->parallel_aware)
        ExecIndexOnlyScanInitializeDSM((IndexOnlyScanState *) planstate,
                         d->pcxt);
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecIndexOnlyScanInstrumentInitDSM((IndexOnlyScanState *) planstate,
                         d->pcxt);
      break;
    case T_BitmapIndexScanState:
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecBitmapIndexScanInitializeDSM((BitmapIndexScanState *) planstate, d->pcxt);
      break;
    case T_ForeignScanState:
      if (planstate->plan->parallel_aware)
        ExecForeignScanInitializeDSM((ForeignScanState *) planstate,
                       d->pcxt);
      break;
    case T_TidRangeScanState:
      if (planstate->plan->parallel_aware)
        ExecTidRangeScanInitializeDSM((TidRangeScanState *) planstate,
                        d->pcxt);
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecTidRangeScanInstrumentInitDSM((TidRangeScanState *) planstate,
                        d->pcxt);
      break;
    case T_AppendState:
      if (planstate->plan->parallel_aware)
        ExecAppendInitializeDSM((AppendState *) planstate,
                    d->pcxt);
      break;
    case T_CustomScanState:
      if (planstate->plan->parallel_aware)
        ExecCustomScanInitializeDSM((CustomScanState *) planstate,
                      d->pcxt);
      break;
    case T_BitmapHeapScanState:
      if (planstate->plan->parallel_aware)
        ExecBitmapHeapInitializeDSM((BitmapHeapScanState *) planstate,
                      d->pcxt);
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecBitmapHeapInstrumentInitDSM((BitmapHeapScanState *) planstate,
                      d->pcxt);
      break;
    case T_HashJoinState:
      if (planstate->plan->parallel_aware)
        ExecHashJoinInitializeDSM((HashJoinState *) planstate,
                      d->pcxt);
      break;
    case T_HashState:
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecHashInitializeDSM((HashState *) planstate, d->pcxt);
      break;
    case T_SortState:
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecSortInitializeDSM((SortState *) planstate, d->pcxt);
      break;
    case T_IncrementalSortState:
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecIncrementalSortInitializeDSM((IncrementalSortState *) planstate, d->pcxt);
      break;
    case T_AggState:
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecAggInitializeDSM((AggState *) planstate, d->pcxt);
      break;
    case T_MemoizeState:
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecMemoizeInitializeDSM((MemoizeState *) planstate, d->pcxt);
      break;
    case T_MaterialState:
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecMaterialInitializeDSM((MaterialState *) planstate, d->pcxt);
      break;
    default:
      break;
  }

  return planstate_tree_walker(planstate, ExecParallelInitializeDSM, d);
}

/*
 * It sets up the response queues for backend workers to return tuples
 * to the main backend and start the workers.
 */
static shm_mq_handle **
ExecParallelSetupTupleQueues(ParallelContext *pcxt, bool reinitialize)
{
  shm_mq_handle **responseq;
  char     *tqueuespace;
  int     i;

  /* Skip this if no workers. */
  if (pcxt->nworkers == 0)
    return NULL;

  /* Allocate memory for shared memory queue handles. */
  responseq = palloc_array(shm_mq_handle *, pcxt->nworkers);

  /*
   * If not reinitializing, allocate space from the DSM for the queues;
   * otherwise, find the already allocated space.
   */
  if (!reinitialize)
    tqueuespace =
      shm_toc_allocate(pcxt->toc,
               mul_size(PARALLEL_TUPLE_QUEUE_SIZE,
                    pcxt->nworkers));
  else
    tqueuespace = shm_toc_lookup(pcxt->toc, PARALLEL_KEY_TUPLE_QUEUE, false);

  /* Create the queues, and become the receiver for each. */
  for (i = 0; i < pcxt->nworkers; ++i)
  {
    shm_mq     *mq;

    mq = shm_mq_create(tqueuespace +
               ((Size) i) * PARALLEL_TUPLE_QUEUE_SIZE,
               (Size) PARALLEL_TUPLE_QUEUE_SIZE);

    shm_mq_set_receiver(mq, MyProc);
    responseq[i] = shm_mq_attach(mq, pcxt->seg, NULL);
  }

  /* Add array of queues to shm_toc, so others can find it. */
  if (!reinitialize)
    shm_toc_insert(pcxt->toc, PARALLEL_KEY_TUPLE_QUEUE, tqueuespace);

  /* Return array of handles. */
  return responseq;
}

/*
 * Sets up the required infrastructure for backend workers to perform
 * execution and return results to the main backend.
 */
ParallelExecutorInfo *
ExecInitParallelPlan(PlanState *planstate, EState *estate,
           Bitmapset *sendParams, int nworkers,
           int64 tuples_needed)
{
  ParallelExecutorInfo *pei;
  ParallelContext *pcxt;
  ExecParallelEstimateContext e;
  ExecParallelInitializeDSMContext d;
  FixedParallelExecutorState *fpes;
  char     *pstmt_data;
  char     *pstmt_space;
  char     *paramlistinfo_space;
  BufferUsage *bufusage_space;
  WalUsage   *walusage_space;
  SharedExecutorInstrumentation *instrumentation = NULL;
  SharedJitInstrumentation *jit_instrumentation = NULL;
  int     pstmt_len;
  int     paramlistinfo_len;
  int     instrumentation_len = 0;
  int     jit_instrumentation_len = 0;
  int     instrument_offset = 0;
  Size    dsa_minsize = dsa_minimum_size();
  char     *query_string;
  int     query_len;

  /*
   * Force any initplan outputs that we're going to pass to workers to be
   * evaluated, if they weren't already.
   *
   * For simplicity, we use the EState's per-output-tuple ExprContext here.
   * That risks intra-query memory leakage, since we might pass through here
   * many times before that ExprContext gets reset; but ExecSetParamPlan
   * doesn't normally leak any memory in the context (see its comments), so
   * it doesn't seem worth complicating this function's API to pass it a
   * shorter-lived ExprContext.  This might need to change someday.
   */
  ExecSetParamPlanMulti(sendParams, GetPerTupleExprContext(estate));

  /* Allocate object for return value. */
  pei = palloc0_object(ParallelExecutorInfo);
  pei->finished = false;
  pei->planstate = planstate;

  /* Fix up and serialize plan to be sent to workers. */
  pstmt_data = ExecSerializePlan(planstate->plan, estate);

  /* Create a parallel context. */
  pcxt = CreateParallelContext("postgres", "ParallelQueryMain", nworkers);
  pei->pcxt = pcxt;

  /*
   * Before telling the parallel context to create a dynamic shared memory
   * segment, we need to figure out how big it should be.  Estimate space
   * for the various things we need to store.
   */

  /* Estimate space for fixed-size state. */
  shm_toc_estimate_chunk(&pcxt->estimator,
               sizeof(FixedParallelExecutorState));
  shm_toc_estimate_keys(&pcxt->estimator, 1);

  /* Estimate space for query text. */
  query_len = strlen(estate->es_sourceText);
  shm_toc_estimate_chunk(&pcxt->estimator, query_len + 1);
  shm_toc_estimate_keys(&pcxt->estimator, 1);

  /* Estimate space for serialized PlannedStmt. */
  pstmt_len = strlen(pstmt_data) + 1;
  shm_toc_estimate_chunk(&pcxt->estimator, pstmt_len);
  shm_toc_estimate_keys(&pcxt->estimator, 1);

  /* Estimate space for serialized ParamListInfo. */
  paramlistinfo_len = EstimateParamListSpace(estate->es_param_list_info);
  shm_toc_estimate_chunk(&pcxt->estimator, paramlistinfo_len);
  shm_toc_estimate_keys(&pcxt->estimator, 1);

  /*
   * Estimate space for BufferUsage.
   *
   * If EXPLAIN is not in use and there are no extensions loaded that care,
   * we could skip this.  But we have no way of knowing whether anyone's
   * looking at pgBufferUsage, so do it unconditionally.
   */
  shm_toc_estimate_chunk(&pcxt->estimator,
               mul_size(sizeof(BufferUsage), pcxt->nworkers));
  shm_toc_estimate_keys(&pcxt->estimator, 1);

  /*
   * Same thing for WalUsage.
   */
  shm_toc_estimate_chunk(&pcxt->estimator,
               mul_size(sizeof(WalUsage), pcxt->nworkers));
  shm_toc_estimate_keys(&pcxt->estimator, 1);

  /* Estimate space for tuple queues. */
  shm_toc_estimate_chunk(&pcxt->estimator,
               mul_size(PARALLEL_TUPLE_QUEUE_SIZE, pcxt->nworkers));
  shm_toc_estimate_keys(&pcxt->estimator, 1);

  /*
   * Give parallel-aware nodes a chance to add to the estimates, and get a
   * count of how many PlanState nodes there are.
   */
  e.pcxt = pcxt;
  e.nnodes = 0;
  ExecParallelEstimate(planstate, &e);

  /* Estimate space for instrumentation, if required. */
  if (estate->es_instrument)
  {
    instrumentation_len =
      offsetof(SharedExecutorInstrumentation, plan_node_id) +
      sizeof(int) * e.nnodes;
    instrumentation_len = MAXALIGN(instrumentation_len);
    instrument_offset = instrumentation_len;
    instrumentation_len +=
      mul_size(sizeof(NodeInstrumentation),
           mul_size(e.nnodes, nworkers));
    shm_toc_estimate_chunk(&pcxt->estimator, instrumentation_len);
    shm_toc_estimate_keys(&pcxt->estimator, 1);

    /* Estimate space for JIT instrumentation, if required. */
    if (estate->es_jit_flags != PGJIT_NONE)
    {
      jit_instrumentation_len =
        offsetof(SharedJitInstrumentation, jit_instr) +
        sizeof(JitInstrumentation) * nworkers;
      shm_toc_estimate_chunk(&pcxt->estimator, jit_instrumentation_len);
      shm_toc_estimate_keys(&pcxt->estimator, 1);
    }
  }

  /* Estimate space for DSA area. */
  shm_toc_estimate_chunk(&pcxt->estimator, dsa_minsize);
  shm_toc_estimate_keys(&pcxt->estimator, 1);

  /*
   * InitializeParallelDSM() passes the active snapshot to the parallel
   * worker, which uses it to set es_snapshot.  Make sure we don't set
   * es_snapshot differently in the child.
   */
  Assert(GetActiveSnapshot() == estate->es_snapshot);

  /* Everyone's had a chance to ask for space, so now create the DSM. */
  InitializeParallelDSM(pcxt);

  /*
   * OK, now we have a dynamic shared memory segment, and it should be big
   * enough to store all of the data we estimated we would want to put into
   * it, plus whatever general stuff (not specifically executor-related) the
   * ParallelContext itself needs to store there.  None of the space we
   * asked for has been allocated or initialized yet, though, so do that.
   */

  /* Store fixed-size state. */
  fpes = shm_toc_allocate(pcxt->toc, sizeof(FixedParallelExecutorState));
  fpes->tuples_needed = tuples_needed;
  fpes->param_exec = InvalidDsaPointer;
  fpes->eflags = estate->es_top_eflags;
  fpes->jit_flags = estate->es_jit_flags;
  shm_toc_insert(pcxt->toc, PARALLEL_KEY_EXECUTOR_FIXED, fpes);

  /* Store query string */
  query_string = shm_toc_allocate(pcxt->toc, query_len + 1);
  memcpy(query_string, estate->es_sourceText, query_len + 1);
  shm_toc_insert(pcxt->toc, PARALLEL_KEY_QUERY_TEXT, query_string);

  /* Store serialized PlannedStmt. */
  pstmt_space = shm_toc_allocate(pcxt->toc, pstmt_len);
  memcpy(pstmt_space, pstmt_data, pstmt_len);
  shm_toc_insert(pcxt->toc, PARALLEL_KEY_PLANNEDSTMT, pstmt_space);

  /* Store serialized ParamListInfo. */
  paramlistinfo_space = shm_toc_allocate(pcxt->toc, paramlistinfo_len);
  shm_toc_insert(pcxt->toc, PARALLEL_KEY_PARAMLISTINFO, paramlistinfo_space);
  SerializeParamList(estate->es_param_list_info, &paramlistinfo_space);

  /* Allocate space for each worker's BufferUsage; no need to initialize. */
  bufusage_space = shm_toc_allocate(pcxt->toc,
                    mul_size(sizeof(BufferUsage), pcxt->nworkers));
  shm_toc_insert(pcxt->toc, PARALLEL_KEY_BUFFER_USAGE, bufusage_space);
  pei->buffer_usage = bufusage_space;

  /* Same for WalUsage. */
  walusage_space = shm_toc_allocate(pcxt->toc,
                    mul_size(sizeof(WalUsage), pcxt->nworkers));
  shm_toc_insert(pcxt->toc, PARALLEL_KEY_WAL_USAGE, walusage_space);
  pei->wal_usage = walusage_space;

  /* Set up the tuple queues that the workers will write into. */
  pei->tqueue = ExecParallelSetupTupleQueues(pcxt, false);

  /* We don't need the TupleQueueReaders yet, though. */
  pei->reader = NULL;

  /*
   * If instrumentation options were supplied, allocate space for the data.
   * It only gets partially initialized here; the rest happens during
   * ExecParallelInitializeDSM.
   */
  if (estate->es_instrument)
  {
    NodeInstrumentation *instrument;
    int     i;

    instrumentation = shm_toc_allocate(pcxt->toc, instrumentation_len);
    instrumentation->instrument_options = estate->es_instrument;
    instrumentation->instrument_offset = instrument_offset;
    instrumentation->num_workers = nworkers;
    instrumentation->num_plan_nodes = e.nnodes;
    instrument = GetInstrumentationArray(instrumentation);
    for (i = 0; i < nworkers * e.nnodes; ++i)
      InstrInitNode(&instrument[i], estate->es_instrument, false);
    shm_toc_insert(pcxt->toc, PARALLEL_KEY_INSTRUMENTATION,
             instrumentation);
    pei->instrumentation = instrumentation;

    if (estate->es_jit_flags != PGJIT_NONE)
    {
      jit_instrumentation = shm_toc_allocate(pcxt->toc,
                           jit_instrumentation_len);
      jit_instrumentation->num_workers = nworkers;
      memset(jit_instrumentation->jit_instr, 0,
           sizeof(JitInstrumentation) * nworkers);
      shm_toc_insert(pcxt->toc, PARALLEL_KEY_JIT_INSTRUMENTATION,
               jit_instrumentation);
      pei->jit_instrumentation = jit_instrumentation;
    }
  }

  /*
   * Create a DSA area that can be used by the leader and all workers.
   * (However, if we failed to create a DSM and are using private memory
   * instead, then skip this.)
   */
  if (pcxt->seg != NULL)
  {
    char     *area_space;

    area_space = shm_toc_allocate(pcxt->toc, dsa_minsize);
    shm_toc_insert(pcxt->toc, PARALLEL_KEY_DSA, area_space);
    pei->area = dsa_create_in_place(area_space, dsa_minsize,
                    LWTRANCHE_PARALLEL_QUERY_DSA,
                    pcxt->seg);

    /*
     * Serialize parameters, if any, using DSA storage.  We don't dare use
     * the main parallel query DSM for this because we might relaunch
     * workers after the values have changed (and thus the amount of
     * storage required has changed).
     */
    if (!bms_is_empty(sendParams))
    {
      pei->param_exec = SerializeParamExecParams(estate, sendParams,
                             pei->area);
      fpes->param_exec = pei->param_exec;
    }
  }

  /*
   * Give parallel-aware nodes a chance to initialize their shared data.
   * This also initializes the elements of instrumentation->ps_instrument,
   * if it exists.
   */
  d.pcxt = pcxt;
  d.instrumentation = instrumentation;
  d.nnodes = 0;

  /* Install our DSA area while initializing the plan. */
  estate->es_query_dsa = pei->area;
  ExecParallelInitializeDSM(planstate, &d);
  estate->es_query_dsa = NULL;

  /*
   * Make sure that the world hasn't shifted under our feet.  This could
   * probably just be an Assert(), but let's be conservative for now.
   */
  if (e.nnodes != d.nnodes)
    elog(ERROR, "inconsistent count of PlanState nodes");

  /* OK, we're ready to rock and roll. */
  return pei;
}

/*
 * Set up tuple queue readers to read the results of a parallel subplan.
 *
 * This is separate from ExecInitParallelPlan() because we can launch the
 * worker processes and let them start doing something before we do this.
 */
void
ExecParallelCreateReaders(ParallelExecutorInfo *pei)
{
  int     nworkers = pei->pcxt->nworkers_launched;
  int     i;

  Assert(pei->reader == NULL);

  if (nworkers > 0)
  {
    pei->reader = palloc_array(TupleQueueReader *, nworkers);

    for (i = 0; i < nworkers; i++)
    {
      shm_mq_set_handle(pei->tqueue[i],
                pei->pcxt->worker[i].bgwhandle);
      pei->reader[i] = CreateTupleQueueReader(pei->tqueue[i]);
    }
  }
}

/*
 * Re-initialize the parallel executor shared memory state before launching
 * a fresh batch of workers.
 */
void
ExecParallelReinitialize(PlanState *planstate,
             ParallelExecutorInfo *pei,
             Bitmapset *sendParams)
{
  EState     *estate = planstate->state;
  FixedParallelExecutorState *fpes;

  /* Old workers must already be shut down */
  Assert(pei->finished);

  /*
   * Force any initplan outputs that we're going to pass to workers to be
   * evaluated, if they weren't already (see comments in
   * ExecInitParallelPlan).
   */
  ExecSetParamPlanMulti(sendParams, GetPerTupleExprContext(estate));

  ReinitializeParallelDSM(pei->pcxt);
  pei->tqueue = ExecParallelSetupTupleQueues(pei->pcxt, true);
  pei->reader = NULL;
  pei->finished = false;

  fpes = shm_toc_lookup(pei->pcxt->toc, PARALLEL_KEY_EXECUTOR_FIXED, false);

  /* Free any serialized parameters from the last round. */
  if (DsaPointerIsValid(fpes->param_exec))
  {
    dsa_free(pei->area, fpes->param_exec);
    fpes->param_exec = InvalidDsaPointer;
  }

  /* Serialize current parameter values if required. */
  if (!bms_is_empty(sendParams))
  {
    pei->param_exec = SerializeParamExecParams(estate, sendParams,
                           pei->area);
    fpes->param_exec = pei->param_exec;
  }

  /* Traverse plan tree and let each child node reset associated state. */
  estate->es_query_dsa = pei->area;
  ExecParallelReInitializeDSM(planstate, pei->pcxt);
  estate->es_query_dsa = NULL;
}

/*
 * Traverse plan tree to reinitialize per-node dynamic shared memory state
 */
static bool
ExecParallelReInitializeDSM(PlanState *planstate,
              ParallelContext *pcxt)
{
  if (planstate == NULL)
    return false;

  /*
   * Call reinitializers for DSM-using plan nodes.
   */
  switch (nodeTag(planstate))
  {
    case T_SeqScanState:
      if (planstate->plan->parallel_aware)
        ExecSeqScanReInitializeDSM((SeqScanState *) planstate,
                       pcxt);
      break;
    case T_IndexScanState:
      if (planstate->plan->parallel_aware)
        ExecIndexScanReInitializeDSM((IndexScanState *) planstate,
                       pcxt);
      break;
    case T_IndexOnlyScanState:
      if (planstate->plan->parallel_aware)
        ExecIndexOnlyScanReInitializeDSM((IndexOnlyScanState *) planstate,
                         pcxt);
      break;
    case T_ForeignScanState:
      if (planstate->plan->parallel_aware)
        ExecForeignScanReInitializeDSM((ForeignScanState *) planstate,
                         pcxt);
      break;
    case T_TidRangeScanState:
      if (planstate->plan->parallel_aware)
        ExecTidRangeScanReInitializeDSM((TidRangeScanState *) planstate,
                        pcxt);
      break;
    case T_AppendState:
      if (planstate->plan->parallel_aware)
        ExecAppendReInitializeDSM((AppendState *) planstate, pcxt);
      break;
    case T_CustomScanState:
      if (planstate->plan->parallel_aware)
        ExecCustomScanReInitializeDSM((CustomScanState *) planstate,
                        pcxt);
      break;
    case T_BitmapHeapScanState:
      if (planstate->plan->parallel_aware)
        ExecBitmapHeapReInitializeDSM((BitmapHeapScanState *) planstate,
                        pcxt);
      break;
    case T_HashJoinState:
      if (planstate->plan->parallel_aware)
        ExecHashJoinReInitializeDSM((HashJoinState *) planstate,
                      pcxt);
      break;
    case T_BitmapIndexScanState:
    case T_HashState:
    case T_SortState:
    case T_IncrementalSortState:
    case T_MemoizeState:
    case T_MaterialState:
      /* these nodes have DSM state, but no reinitialization is required */
      break;

    default:
      break;
  }

  return planstate_tree_walker(planstate, ExecParallelReInitializeDSM, pcxt);
}

/*
 * Copy instrumentation information about this node and its descendants from
 * dynamic shared memory.
 */
static bool
ExecParallelRetrieveInstrumentation(PlanState *planstate,
                  SharedExecutorInstrumentation *instrumentation)
{
  NodeInstrumentation *instrument;
  int     i;
  int     n;
  int     ibytes;
  int     plan_node_id = planstate->plan->plan_node_id;
  MemoryContext oldcontext;

  /* Find the instrumentation for this node. */
  for (i = 0; i < instrumentation->num_plan_nodes; ++i)
    if (instrumentation->plan_node_id[i] == plan_node_id)
      break;
  if (i >= instrumentation->num_plan_nodes)
    elog(ERROR, "plan node %d not found", plan_node_id);

  /* Accumulate the statistics from all workers. */
  instrument = GetInstrumentationArray(instrumentation);
  instrument += i * instrumentation->num_workers;
  for (n = 0; n < instrumentation->num_workers; ++n)
    InstrAggNode(planstate->instrument, &instrument[n]);

  /*
   * Also store the per-worker detail.
   *
   * Worker instrumentation should be allocated in the same context as the
   * regular instrumentation information, which is the per-query context.
   * Switch into per-query memory context.
   */
  oldcontext = MemoryContextSwitchTo(planstate->state->es_query_cxt);
  ibytes = mul_size(instrumentation->num_workers, sizeof(NodeInstrumentation));
  planstate->worker_instrument =
    palloc(ibytes + offsetof(WorkerNodeInstrumentation, instrument));
  MemoryContextSwitchTo(oldcontext);

  planstate->worker_instrument->num_workers = instrumentation->num_workers;
  memcpy(planstate->worker_instrument->instrument, instrument, ibytes);

  /* Perform any node-type-specific work that needs to be done. */
  switch (nodeTag(planstate))
  {
    case T_IndexScanState:
      ExecIndexScanRetrieveInstrumentation((IndexScanState *) planstate);
      break;
    case T_IndexOnlyScanState:
      ExecIndexOnlyScanRetrieveInstrumentation((IndexOnlyScanState *) planstate);
      break;
    case T_BitmapIndexScanState:
      ExecBitmapIndexScanRetrieveInstrumentation((BitmapIndexScanState *) planstate);
      break;
    case T_SortState:
      ExecSortRetrieveInstrumentation((SortState *) planstate);
      break;
    case T_IncrementalSortState:
      ExecIncrementalSortRetrieveInstrumentation((IncrementalSortState *) planstate);
      break;
    case T_HashState:
      ExecHashRetrieveInstrumentation((HashState *) planstate);
      break;
    case T_AggState:
      ExecAggRetrieveInstrumentation((AggState *) planstate);
      break;
    case T_MemoizeState:
      ExecMemoizeRetrieveInstrumentation((MemoizeState *) planstate);
      break;
    case T_MaterialState:
      ExecMaterialRetrieveInstrumentation((MaterialState *) planstate);
      break;
    case T_BitmapHeapScanState:
      ExecBitmapHeapRetrieveInstrumentation((BitmapHeapScanState *) planstate);
      break;
    case T_SeqScanState:
      ExecSeqScanRetrieveInstrumentation((SeqScanState *) planstate);
      break;
    case T_TidRangeScanState:
      ExecTidRangeScanRetrieveInstrumentation((TidRangeScanState *) planstate);
      break;
    default:
      break;
  }

  return planstate_tree_walker(planstate, ExecParallelRetrieveInstrumentation,
                 instrumentation);
}

/*
 * Add up the workers' JIT instrumentation from dynamic shared memory.
 */
static void
ExecParallelRetrieveJitInstrumentation(PlanState *planstate,
                     SharedJitInstrumentation *shared_jit)
{
  JitInstrumentation *combined;
  int     ibytes;

  int     n;

  /*
   * Accumulate worker JIT instrumentation into the combined JIT
   * instrumentation, allocating it if required.
   */
  if (!planstate->state->es_jit_worker_instr)
    planstate->state->es_jit_worker_instr =
      MemoryContextAllocZero(planstate->state->es_query_cxt, sizeof(JitInstrumentation));
  combined = planstate->state->es_jit_worker_instr;

  /* Accumulate all the workers' instrumentations. */
  for (n = 0; n < shared_jit->num_workers; ++n)
    InstrJitAgg(combined, &shared_jit->jit_instr[n]);

  /*
   * Store the per-worker detail.
   *
   * Similar to ExecParallelRetrieveInstrumentation(), allocate the
   * instrumentation in per-query context.
   */
  ibytes = offsetof(SharedJitInstrumentation, jit_instr)
    + mul_size(shared_jit->num_workers, sizeof(JitInstrumentation));
  planstate->worker_jit_instrument =
    MemoryContextAlloc(planstate->state->es_query_cxt, ibytes);

  memcpy(planstate->worker_jit_instrument, shared_jit, ibytes);
}

/*
 * Finish parallel execution.  We wait for parallel workers to finish, and
 * accumulate their buffer/WAL usage.
 */
void
ExecParallelFinish(ParallelExecutorInfo *pei)
{
  int     nworkers = pei->pcxt->nworkers_launched;
  int     i;

  /* Make this be a no-op if called twice in a row. */
  if (pei->finished)
    return;

  /*
   * Detach from tuple queues ASAP, so that any still-active workers will
   * notice that no further results are wanted.
   */
  if (pei->tqueue != NULL)
  {
    for (i = 0; i < nworkers; i++)
      shm_mq_detach(pei->tqueue[i]);
    pfree(pei->tqueue);
    pei->tqueue = NULL;
  }

  /*
   * While we're waiting for the workers to finish, let's get rid of the
   * tuple queue readers.  (Any other local cleanup could be done here too.)
   */
  if (pei->reader != NULL)
  {
    for (i = 0; i < nworkers; i++)
      DestroyTupleQueueReader(pei->reader[i]);
    pfree(pei->reader);
    pei->reader = NULL;
  }

  /* Now wait for the workers to finish. */
  WaitForParallelWorkersToFinish(pei->pcxt);

  /*
   * Next, accumulate buffer/WAL usage.  (This must wait for the workers to
   * finish, or we might get incomplete data.)
   */
  for (i = 0; i < nworkers; i++)
    InstrAccumParallelQuery(&pei->buffer_usage[i], &pei->wal_usage[i]);

  pei->finished = true;
}

/*
 * Accumulate instrumentation, and then clean up whatever ParallelExecutorInfo
 * resources still exist after ExecParallelFinish.  We separate these
 * routines because someone might want to examine the contents of the DSM
 * after ExecParallelFinish and before calling this routine.
 */
void
ExecParallelCleanup(ParallelExecutorInfo *pei)
{
  /* Accumulate instrumentation, if any. */
  if (pei->instrumentation)
    ExecParallelRetrieveInstrumentation(pei->planstate,
                      pei->instrumentation);

  /* Accumulate JIT instrumentation, if any. */
  if (pei->jit_instrumentation)
    ExecParallelRetrieveJitInstrumentation(pei->planstate,
                         pei->jit_instrumentation);

  /* Free any serialized parameters. */
  if (DsaPointerIsValid(pei->param_exec))
  {
    dsa_free(pei->area, pei->param_exec);
    pei->param_exec = InvalidDsaPointer;
  }
  if (pei->area != NULL)
  {
    dsa_detach(pei->area);
    pei->area = NULL;
  }
  if (pei->pcxt != NULL)
  {
    DestroyParallelContext(pei->pcxt);
    pei->pcxt = NULL;
  }
  pfree(pei);
}

/*
 * Create a DestReceiver to write tuples we produce to the shm_mq designated
 * for that purpose.
 */
static DestReceiver *
ExecParallelGetReceiver(dsm_segment *seg, shm_toc *toc)
{
  char     *mqspace;
  shm_mq     *mq;

  mqspace = shm_toc_lookup(toc, PARALLEL_KEY_TUPLE_QUEUE, false);
  mqspace += ParallelWorkerNumber * PARALLEL_TUPLE_QUEUE_SIZE;
  mq = (shm_mq *) mqspace;
  shm_mq_set_sender(mq, MyProc);
  return CreateTupleQueueDestReceiver(shm_mq_attach(mq, seg, NULL));
}

/*
 * Create a QueryDesc for the PlannedStmt we are to execute, and return it.
 */
static QueryDesc *
ExecParallelGetQueryDesc(shm_toc *toc, DestReceiver *receiver,
             int instrument_options)
{
  char     *pstmtspace;
  char     *paramspace;
  PlannedStmt *pstmt;
  ParamListInfo paramLI;
  char     *queryString;

  /* Get the query string from shared memory */
  queryString = shm_toc_lookup(toc, PARALLEL_KEY_QUERY_TEXT, false);

  /* Reconstruct leader-supplied PlannedStmt. */
  pstmtspace = shm_toc_lookup(toc, PARALLEL_KEY_PLANNEDSTMT, false);
  pstmt = (PlannedStmt *) stringToNode(pstmtspace);

  /* Reconstruct ParamListInfo. */
  paramspace = shm_toc_lookup(toc, PARALLEL_KEY_PARAMLISTINFO, false);
  paramLI = RestoreParamList(&paramspace);

  /* Create a QueryDesc for the query. */
  return CreateQueryDesc(pstmt,
               queryString,
               GetActiveSnapshot(), InvalidSnapshot,
               receiver, paramLI, NULL, instrument_options);
}

/*
 * Copy instrumentation information from this node and its descendants into
 * dynamic shared memory, so that the parallel leader can retrieve it.
 */
static bool
ExecParallelReportInstrumentation(PlanState *planstate,
                  SharedExecutorInstrumentation *instrumentation)
{
  int     i;
  int     plan_node_id = planstate->plan->plan_node_id;
  NodeInstrumentation *instrument;

  InstrEndLoop(planstate->instrument);

  /*
   * If we shuffled the plan_node_id values in ps_instrument into sorted
   * order, we could use binary search here.  This might matter someday if
   * we're pushing down sufficiently large plan trees.  For now, do it the
   * slow, dumb way.
   */
  for (i = 0; i < instrumentation->num_plan_nodes; ++i)
    if (instrumentation->plan_node_id[i] == plan_node_id)
      break;
  if (i >= instrumentation->num_plan_nodes)
    elog(ERROR, "plan node %d not found", plan_node_id);

  /*
   * Add our statistics to the per-node, per-worker totals.  It's possible
   * that this could happen more than once if we relaunched workers.
   */
  instrument = GetInstrumentationArray(instrumentation);
  instrument += i * instrumentation->num_workers;
  Assert(IsParallelWorker());
  Assert(ParallelWorkerNumber < instrumentation->num_workers);
  InstrAggNode(&instrument[ParallelWorkerNumber], planstate->instrument);

  return planstate_tree_walker(planstate, ExecParallelReportInstrumentation,
                 instrumentation);
}

/*
 * Initialize the PlanState and its descendants with the information
 * retrieved from shared memory.  This has to be done once the PlanState
 * is allocated and initialized by executor; that is, after ExecutorStart().
 */
static bool
ExecParallelInitializeWorker(PlanState *planstate, ParallelWorkerContext *pwcxt)
{
  if (planstate == NULL)
    return false;

  switch (nodeTag(planstate))
  {
    case T_SeqScanState:
      if (planstate->plan->parallel_aware)
        ExecSeqScanInitializeWorker((SeqScanState *) planstate, pwcxt);
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecSeqScanInstrumentInitWorker((SeqScanState *) planstate, pwcxt);
      break;
    case T_IndexScanState:
      if (planstate->plan->parallel_aware)
        ExecIndexScanInitializeWorker((IndexScanState *) planstate,
                        pwcxt);
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecIndexScanInstrumentInitWorker((IndexScanState *) planstate,
                        pwcxt);
      break;
    case T_IndexOnlyScanState:
      if (planstate->plan->parallel_aware)
        ExecIndexOnlyScanInitializeWorker((IndexOnlyScanState *) planstate,
                          pwcxt);
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecIndexOnlyScanInstrumentInitWorker((IndexOnlyScanState *) planstate,
                          pwcxt);
      break;
    case T_BitmapIndexScanState:
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecBitmapIndexScanInitializeWorker((BitmapIndexScanState *) planstate,
                        pwcxt);
      break;
    case T_ForeignScanState:
      if (planstate->plan->parallel_aware)
        ExecForeignScanInitializeWorker((ForeignScanState *) planstate,
                        pwcxt);
      break;
    case T_TidRangeScanState:
      if (planstate->plan->parallel_aware)
        ExecTidRangeScanInitializeWorker((TidRangeScanState *) planstate,
                         pwcxt);
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecTidRangeScanInstrumentInitWorker((TidRangeScanState *) planstate,
                         pwcxt);
      break;
    case T_AppendState:
      if (planstate->plan->parallel_aware)
        ExecAppendInitializeWorker((AppendState *) planstate, pwcxt);
      break;
    case T_CustomScanState:
      if (planstate->plan->parallel_aware)
        ExecCustomScanInitializeWorker((CustomScanState *) planstate,
                         pwcxt);
      break;
    case T_BitmapHeapScanState:
      if (planstate->plan->parallel_aware)
        ExecBitmapHeapInitializeWorker((BitmapHeapScanState *) planstate,
                         pwcxt);
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecBitmapHeapInstrumentInitWorker((BitmapHeapScanState *) planstate,
                         pwcxt);
      break;
    case T_HashJoinState:
      if (planstate->plan->parallel_aware)
        ExecHashJoinInitializeWorker((HashJoinState *) planstate,
                       pwcxt);
      break;
    case T_HashState:
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecHashInitializeWorker((HashState *) planstate, pwcxt);
      break;
    case T_SortState:
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecSortInitializeWorker((SortState *) planstate, pwcxt);
      break;
    case T_IncrementalSortState:
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecIncrementalSortInitializeWorker((IncrementalSortState *) planstate,
                        pwcxt);
      break;
    case T_AggState:
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecAggInitializeWorker((AggState *) planstate, pwcxt);
      break;
    case T_MemoizeState:
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecMemoizeInitializeWorker((MemoizeState *) planstate, pwcxt);
      break;
    case T_MaterialState:
      /* even when not parallel-aware, for EXPLAIN ANALYZE */
      ExecMaterialInitializeWorker((MaterialState *) planstate, pwcxt);
      break;
    default:
      break;
  }

  return planstate_tree_walker(planstate, ExecParallelInitializeWorker,
                 pwcxt);
}

/*
 * Main entrypoint for parallel query worker processes.
 *
 * We reach this function from ParallelWorkerMain, so the setup necessary to
 * create a sensible parallel environment has already been done;
 * ParallelWorkerMain worries about stuff like the transaction state, combo
 * CID mappings, and GUC values, so we don't need to deal with any of that
 * here.
 *
 * Our job is to deal with concerns specific to the executor.  The parallel
 * group leader will have stored a serialized PlannedStmt, and it's our job
 * to execute that plan and write the resulting tuples to the appropriate
 * tuple queue.  Various bits of supporting information that we need in order
 * to do this are also stored in the dsm_segment and can be accessed through
 * the shm_toc.
 */
void
ParallelQueryMain(dsm_segment *seg, shm_toc *toc)
{
  FixedParallelExecutorState *fpes;
  BufferUsage *buffer_usage;
  WalUsage   *wal_usage;
  DestReceiver *receiver;
  QueryDesc  *queryDesc;
  SharedExecutorInstrumentation *instrumentation;
  SharedJitInstrumentation *jit_instrumentation;
  int     instrument_options = 0;
  void     *area_space;
  dsa_area   *area;
  ParallelWorkerContext pwcxt;

  /* Get fixed-size state. */
  fpes = shm_toc_lookup(toc, PARALLEL_KEY_EXECUTOR_FIXED, false);

  /* Set up DestReceiver, SharedExecutorInstrumentation, and QueryDesc. */
  receiver = ExecParallelGetReceiver(seg, toc);
  instrumentation = shm_toc_lookup(toc, PARALLEL_KEY_INSTRUMENTATION, true);
  if (instrumentation != NULL)
    instrument_options = instrumentation->instrument_options;
  jit_instrumentation = shm_toc_lookup(toc, PARALLEL_KEY_JIT_INSTRUMENTATION,
                     true);
  queryDesc = ExecParallelGetQueryDesc(toc, receiver, instrument_options);

  /* Setting debug_query_string for individual workers */
  debug_query_string = queryDesc->sourceText;

  /* Report workers' query for monitoring purposes */
  pgstat_report_activity(STATE_RUNNING, debug_query_string);

  /* Attach to the dynamic shared memory area. */
  area_space = shm_toc_lookup(toc, PARALLEL_KEY_DSA, false);
  area = dsa_attach_in_place(area_space, seg);

  /* Start up the executor */
  queryDesc->plannedstmt->jitFlags = fpes->jit_flags;
  ExecutorStart(queryDesc, fpes->eflags);

  /* Special executor initialization steps for parallel workers */
  queryDesc->planstate->state->es_query_dsa = area;
  if (DsaPointerIsValid(fpes->param_exec))
  {
    char     *paramexec_space;

    paramexec_space = dsa_get_address(area, fpes->param_exec);
    RestoreParamExecParams(paramexec_space, queryDesc->estate);
  }
  pwcxt.toc = toc;
  pwcxt.seg = seg;
  ExecParallelInitializeWorker(queryDesc->planstate, &pwcxt);

  /* Pass down any tuple bound */
  ExecSetTupleBound(fpes->tuples_needed, queryDesc->planstate);

  /*
   * Prepare to track buffer/WAL usage during query execution.
   *
   * We do this after starting up the executor to match what happens in the
   * leader, which also doesn't count buffer accesses and WAL activity that
   * occur during executor startup.
   */
  InstrStartParallelQuery();

  /*
   * Run the plan.  If we specified a tuple bound, be careful not to demand
   * more tuples than that.
   */
  ExecutorRun(queryDesc,
        ForwardScanDirection,
        fpes->tuples_needed < 0 ? (int64) 0 : fpes->tuples_needed);

  /* Shut down the executor */
  ExecutorFinish(queryDesc);

  /* Report buffer/WAL usage during parallel execution. */
  buffer_usage = shm_toc_lookup(toc, PARALLEL_KEY_BUFFER_USAGE, false);
  wal_usage = shm_toc_lookup(toc, PARALLEL_KEY_WAL_USAGE, false);
  InstrEndParallelQuery(&buffer_usage[ParallelWorkerNumber],
              &wal_usage[ParallelWorkerNumber]);

  /* Report instrumentation data if any instrumentation options are set. */
  if (instrumentation != NULL)
    ExecParallelReportInstrumentation(queryDesc->planstate,
                      instrumentation);

  /* Report JIT instrumentation data if any */
  if (queryDesc->estate->es_jit && jit_instrumentation != NULL)
  {
    Assert(ParallelWorkerNumber < jit_instrumentation->num_workers);
    jit_instrumentation->jit_instr[ParallelWorkerNumber] =
      queryDesc->estate->es_jit->instr;
  }

  /* Must do this after capturing instrumentation. */
  ExecutorEnd(queryDesc);

  /* Cleanup. */
  dsa_detach(area);
  FreeQueryDesc(queryDesc);
  receiver->rDestroy(receiver);
}

Coverage Report

Created: 2026-10-16 06:48