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+/*-------------------------------------------------------------------------
+ *
+ * nodeAppend.c
+ * routines to handle append nodes.
+ *
+ * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ * src/backend/executor/nodeAppend.c
+ *
+ *-------------------------------------------------------------------------
+ */
+/* INTERFACE ROUTINES
+ * ExecInitAppend - initialize the append node
+ * ExecAppend - retrieve the next tuple from the node
+ * ExecEndAppend - shut down the append node
+ * ExecReScanAppend - rescan the append node
+ *
+ * NOTES
+ * Each append node contains a list of one or more subplans which
+ * must be iteratively processed (forwards or backwards).
+ * Tuples are retrieved by executing the 'whichplan'th subplan
+ * until the subplan stops returning tuples, at which point that
+ * plan is shut down and the next started up.
+ *
+ * Append nodes don't make use of their left and right
+ * subtrees, rather they maintain a list of subplans so
+ * a typical append node looks like this in the plan tree:
+ *
+ * ...
+ * /
+ * Append -------+------+------+--- nil
+ * / \ | | |
+ * nil nil ... ... ...
+ * subplans
+ *
+ * Append nodes are currently used for unions, and to support
+ * inheritance queries, where several relations need to be scanned.
+ * For example, in our standard person/student/employee/student-emp
+ * example, where student and employee inherit from person
+ * and student-emp inherits from student and employee, the
+ * query:
+ *
+ * select name from person
+ *
+ * generates the plan:
+ *
+ * |
+ * Append -------+-------+--------+--------+
+ * / \ | | | |
+ * nil nil Scan Scan Scan Scan
+ * | | | |
+ * person employee student student-emp
+ */
+
+#include "postgres.h"
+
+#include "executor/execdebug.h"
+#include "executor/execPartition.h"
+#include "executor/nodeAppend.h"
+#include "miscadmin.h"
+
+/* Shared state for parallel-aware Append. */
+struct ParallelAppendState
+{
+ LWLock pa_lock; /* mutual exclusion to choose next subplan */
+ int pa_next_plan; /* next plan to choose by any worker */
+
+ /*
+ * pa_finished[i] should be true if no more workers should select subplan
+ * i. for a non-partial plan, this should be set to true as soon as a
+ * worker selects the plan; for a partial plan, it remains false until
+ * some worker executes the plan to completion.
+ */
+ bool pa_finished[FLEXIBLE_ARRAY_MEMBER];
+};
+
+#define INVALID_SUBPLAN_INDEX -1
+
+static TupleTableSlot *ExecAppend(PlanState *pstate);
+static bool choose_next_subplan_locally(AppendState *node);
+static bool choose_next_subplan_for_leader(AppendState *node);
+static bool choose_next_subplan_for_worker(AppendState *node);
+static void mark_invalid_subplans_as_finished(AppendState *node);
+
+/* ----------------------------------------------------------------
+ * ExecInitAppend
+ *
+ * Begin all of the subscans of the append node.
+ *
+ * (This is potentially wasteful, since the entire result of the
+ * append node may not be scanned, but this way all of the
+ * structures get allocated in the executor's top level memory
+ * block instead of that of the call to ExecAppend.)
+ * ----------------------------------------------------------------
+ */
+AppendState *
+ExecInitAppend(Append *node, EState *estate, int eflags)
+{
+ AppendState *appendstate = makeNode(AppendState);
+ PlanState **appendplanstates;
+ Bitmapset *validsubplans;
+ int nplans;
+ int firstvalid;
+ int i,
+ j;
+
+ /* check for unsupported flags */
+ Assert(!(eflags & EXEC_FLAG_MARK));
+
+ /*
+ * create new AppendState for our append node
+ */
+ appendstate->ps.plan = (Plan *) node;
+ appendstate->ps.state = estate;
+ appendstate->ps.ExecProcNode = ExecAppend;
+
+ /* Let choose_next_subplan_* function handle setting the first subplan */
+ appendstate->as_whichplan = INVALID_SUBPLAN_INDEX;
+
+ /* If run-time partition pruning is enabled, then set that up now */
+ if (node->part_prune_info != NULL)
+ {
+ PartitionPruneState *prunestate;
+
+ /* We may need an expression context to evaluate partition exprs */
+ ExecAssignExprContext(estate, &appendstate->ps);
+
+ /* Create the working data structure for pruning. */
+ prunestate = ExecCreatePartitionPruneState(&appendstate->ps,
+ node->part_prune_info);
+ appendstate->as_prune_state = prunestate;
+
+ /* Perform an initial partition prune, if required. */
+ if (prunestate->do_initial_prune)
+ {
+ /* Determine which subplans survive initial pruning */
+ validsubplans = ExecFindInitialMatchingSubPlans(prunestate,
+ list_length(node->appendplans));
+
+ nplans = bms_num_members(validsubplans);
+ }
+ else
+ {
+ /* We'll need to initialize all subplans */
+ nplans = list_length(node->appendplans);
+ Assert(nplans > 0);
+ validsubplans = bms_add_range(NULL, 0, nplans - 1);
+ }
+
+ /*
+ * When no run-time pruning is required and there's at least one
+ * subplan, we can fill as_valid_subplans immediately, preventing
+ * later calls to ExecFindMatchingSubPlans.
+ */
+ if (!prunestate->do_exec_prune && nplans > 0)
+ appendstate->as_valid_subplans = bms_add_range(NULL, 0, nplans - 1);
+ }
+ else
+ {
+ nplans = list_length(node->appendplans);
+
+ /*
+ * When run-time partition pruning is not enabled we can just mark all
+ * subplans as valid; they must also all be initialized.
+ */
+ Assert(nplans > 0);
+ appendstate->as_valid_subplans = validsubplans =
+ bms_add_range(NULL, 0, nplans - 1);
+ appendstate->as_prune_state = NULL;
+ }
+
+ /*
+ * Initialize result tuple type and slot.
+ */
+ ExecInitResultTupleSlotTL(&appendstate->ps, &TTSOpsVirtual);
+
+ /* node returns slots from each of its subnodes, therefore not fixed */
+ appendstate->ps.resultopsset = true;
+ appendstate->ps.resultopsfixed = false;
+
+ appendplanstates = (PlanState **) palloc(nplans *
+ sizeof(PlanState *));
+
+ /*
+ * call ExecInitNode on each of the valid plans to be executed and save
+ * the results into the appendplanstates array.
+ *
+ * While at it, find out the first valid partial plan.
+ */
+ j = 0;
+ firstvalid = nplans;
+ i = -1;
+ while ((i = bms_next_member(validsubplans, i)) >= 0)
+ {
+ Plan *initNode = (Plan *) list_nth(node->appendplans, i);
+
+ /*
+ * Record the lowest appendplans index which is a valid partial plan.
+ */
+ if (i >= node->first_partial_plan && j < firstvalid)
+ firstvalid = j;
+
+ appendplanstates[j++] = ExecInitNode(initNode, estate, eflags);
+ }
+
+ appendstate->as_first_partial_plan = firstvalid;
+ appendstate->appendplans = appendplanstates;
+ appendstate->as_nplans = nplans;
+
+ /*
+ * Miscellaneous initialization
+ */
+
+ appendstate->ps.ps_ProjInfo = NULL;
+
+ /* For parallel query, this will be overridden later. */
+ appendstate->choose_next_subplan = choose_next_subplan_locally;
+
+ return appendstate;
+}
+
+/* ----------------------------------------------------------------
+ * ExecAppend
+ *
+ * Handles iteration over multiple subplans.
+ * ----------------------------------------------------------------
+ */
+static TupleTableSlot *
+ExecAppend(PlanState *pstate)
+{
+ AppendState *node = castNode(AppendState, pstate);
+
+ if (node->as_whichplan < 0)
+ {
+ /* Nothing to do if there are no subplans */
+ if (node->as_nplans == 0)
+ return ExecClearTuple(node->ps.ps_ResultTupleSlot);
+
+ /*
+ * If no subplan has been chosen, we must choose one before
+ * proceeding.
+ */
+ if (node->as_whichplan == INVALID_SUBPLAN_INDEX &&
+ !node->choose_next_subplan(node))
+ return ExecClearTuple(node->ps.ps_ResultTupleSlot);
+ }
+
+ for (;;)
+ {
+ PlanState *subnode;
+ TupleTableSlot *result;
+
+ CHECK_FOR_INTERRUPTS();
+
+ /*
+ * figure out which subplan we are currently processing
+ */
+ Assert(node->as_whichplan >= 0 && node->as_whichplan < node->as_nplans);
+ subnode = node->appendplans[node->as_whichplan];
+
+ /*
+ * get a tuple from the subplan
+ */
+ result = ExecProcNode(subnode);
+
+ if (!TupIsNull(result))
+ {
+ /*
+ * If the subplan gave us something then return it as-is. We do
+ * NOT make use of the result slot that was set up in
+ * ExecInitAppend; there's no need for it.
+ */
+ return result;
+ }
+
+ /* choose new subplan; if none, we're done */
+ if (!node->choose_next_subplan(node))
+ return ExecClearTuple(node->ps.ps_ResultTupleSlot);
+ }
+}
+
+/* ----------------------------------------------------------------
+ * ExecEndAppend
+ *
+ * Shuts down the subscans of the append node.
+ *
+ * Returns nothing of interest.
+ * ----------------------------------------------------------------
+ */
+void
+ExecEndAppend(AppendState *node)
+{
+ PlanState **appendplans;
+ int nplans;
+ int i;
+
+ /*
+ * get information from the node
+ */
+ appendplans = node->appendplans;
+ nplans = node->as_nplans;
+
+ /*
+ * shut down each of the subscans
+ */
+ for (i = 0; i < nplans; i++)
+ ExecEndNode(appendplans[i]);
+}
+
+void
+ExecReScanAppend(AppendState *node)
+{
+ int i;
+
+ /*
+ * If any PARAM_EXEC Params used in pruning expressions have changed, then
+ * we'd better unset the valid subplans so that they are reselected for
+ * the new parameter values.
+ */
+ if (node->as_prune_state &&
+ bms_overlap(node->ps.chgParam,
+ node->as_prune_state->execparamids))
+ {
+ bms_free(node->as_valid_subplans);
+ node->as_valid_subplans = NULL;
+ }
+
+ for (i = 0; i < node->as_nplans; i++)
+ {
+ PlanState *subnode = node->appendplans[i];
+
+ /*
+ * ExecReScan doesn't know about my subplans, so I have to do
+ * changed-parameter signaling myself.
+ */
+ if (node->ps.chgParam != NULL)
+ UpdateChangedParamSet(subnode, node->ps.chgParam);
+
+ /*
+ * If chgParam of subnode is not null then plan will be re-scanned by
+ * first ExecProcNode.
+ */
+ if (subnode->chgParam == NULL)
+ ExecReScan(subnode);
+ }
+
+ /* Let choose_next_subplan_* function handle setting the first subplan */
+ node->as_whichplan = INVALID_SUBPLAN_INDEX;
+}
+
+/* ----------------------------------------------------------------
+ * Parallel Append Support
+ * ----------------------------------------------------------------
+ */
+
+/* ----------------------------------------------------------------
+ * ExecAppendEstimate
+ *
+ * Compute the amount of space we'll need in the parallel
+ * query DSM, and inform pcxt->estimator about our needs.
+ * ----------------------------------------------------------------
+ */
+void
+ExecAppendEstimate(AppendState *node,
+ ParallelContext *pcxt)
+{
+ node->pstate_len =
+ add_size(offsetof(ParallelAppendState, pa_finished),
+ sizeof(bool) * node->as_nplans);
+
+ shm_toc_estimate_chunk(&pcxt->estimator, node->pstate_len);
+ shm_toc_estimate_keys(&pcxt->estimator, 1);
+}
+
+
+/* ----------------------------------------------------------------
+ * ExecAppendInitializeDSM
+ *
+ * Set up shared state for Parallel Append.
+ * ----------------------------------------------------------------
+ */
+void
+ExecAppendInitializeDSM(AppendState *node,
+ ParallelContext *pcxt)
+{
+ ParallelAppendState *pstate;
+
+ pstate = shm_toc_allocate(pcxt->toc, node->pstate_len);
+ memset(pstate, 0, node->pstate_len);
+ LWLockInitialize(&pstate->pa_lock, LWTRANCHE_PARALLEL_APPEND);
+ shm_toc_insert(pcxt->toc, node->ps.plan->plan_node_id, pstate);
+
+ node->as_pstate = pstate;
+ node->choose_next_subplan = choose_next_subplan_for_leader;
+}
+
+/* ----------------------------------------------------------------
+ * ExecAppendReInitializeDSM
+ *
+ * Reset shared state before beginning a fresh scan.
+ * ----------------------------------------------------------------
+ */
+void
+ExecAppendReInitializeDSM(AppendState *node, ParallelContext *pcxt)
+{
+ ParallelAppendState *pstate = node->as_pstate;
+
+ pstate->pa_next_plan = 0;
+ memset(pstate->pa_finished, 0, sizeof(bool) * node->as_nplans);
+}
+
+/* ----------------------------------------------------------------
+ * ExecAppendInitializeWorker
+ *
+ * Copy relevant information from TOC into planstate, and initialize
+ * whatever is required to choose and execute the optimal subplan.
+ * ----------------------------------------------------------------
+ */
+void
+ExecAppendInitializeWorker(AppendState *node, ParallelWorkerContext *pwcxt)
+{
+ node->as_pstate = shm_toc_lookup(pwcxt->toc, node->ps.plan->plan_node_id, false);
+ node->choose_next_subplan = choose_next_subplan_for_worker;
+}
+
+/* ----------------------------------------------------------------
+ * choose_next_subplan_locally
+ *
+ * Choose next subplan for a non-parallel-aware Append,
+ * returning false if there are no more.
+ * ----------------------------------------------------------------
+ */
+static bool
+choose_next_subplan_locally(AppendState *node)
+{
+ int whichplan = node->as_whichplan;
+ int nextplan;
+
+ /* We should never be called when there are no subplans */
+ Assert(node->as_nplans > 0);
+
+ /*
+ * If first call then have the bms member function choose the first valid
+ * subplan by initializing whichplan to -1. If there happen to be no
+ * valid subplans then the bms member function will handle that by
+ * returning a negative number which will allow us to exit returning a
+ * false value.
+ */
+ if (whichplan == INVALID_SUBPLAN_INDEX)
+ {
+ if (node->as_valid_subplans == NULL)
+ node->as_valid_subplans =
+ ExecFindMatchingSubPlans(node->as_prune_state);
+
+ whichplan = -1;
+ }
+
+ /* Ensure whichplan is within the expected range */
+ Assert(whichplan >= -1 && whichplan <= node->as_nplans);
+
+ if (ScanDirectionIsForward(node->ps.state->es_direction))
+ nextplan = bms_next_member(node->as_valid_subplans, whichplan);
+ else
+ nextplan = bms_prev_member(node->as_valid_subplans, whichplan);
+
+ if (nextplan < 0)
+ return false;
+
+ node->as_whichplan = nextplan;
+
+ return true;
+}
+
+/* ----------------------------------------------------------------
+ * choose_next_subplan_for_leader
+ *
+ * Try to pick a plan which doesn't commit us to doing much
+ * work locally, so that as much work as possible is done in
+ * the workers. Cheapest subplans are at the end.
+ * ----------------------------------------------------------------
+ */
+static bool
+choose_next_subplan_for_leader(AppendState *node)
+{
+ ParallelAppendState *pstate = node->as_pstate;
+
+ /* Backward scan is not supported by parallel-aware plans */
+ Assert(ScanDirectionIsForward(node->ps.state->es_direction));
+
+ /* We should never be called when there are no subplans */
+ Assert(node->as_nplans > 0);
+
+ LWLockAcquire(&pstate->pa_lock, LW_EXCLUSIVE);
+
+ if (node->as_whichplan != INVALID_SUBPLAN_INDEX)
+ {
+ /* Mark just-completed subplan as finished. */
+ node->as_pstate->pa_finished[node->as_whichplan] = true;
+ }
+ else
+ {
+ /* Start with last subplan. */
+ node->as_whichplan = node->as_nplans - 1;
+
+ /*
+ * If we've yet to determine the valid subplans then do so now. If
+ * run-time pruning is disabled then the valid subplans will always be
+ * set to all subplans.
+ */
+ if (node->as_valid_subplans == NULL)
+ {
+ node->as_valid_subplans =
+ ExecFindMatchingSubPlans(node->as_prune_state);
+
+ /*
+ * Mark each invalid plan as finished to allow the loop below to
+ * select the first valid subplan.
+ */
+ mark_invalid_subplans_as_finished(node);
+ }
+ }
+
+ /* Loop until we find a subplan to execute. */
+ while (pstate->pa_finished[node->as_whichplan])
+ {
+ if (node->as_whichplan == 0)
+ {
+ pstate->pa_next_plan = INVALID_SUBPLAN_INDEX;
+ node->as_whichplan = INVALID_SUBPLAN_INDEX;
+ LWLockRelease(&pstate->pa_lock);
+ return false;
+ }
+
+ /*
+ * We needn't pay attention to as_valid_subplans here as all invalid
+ * plans have been marked as finished.
+ */
+ node->as_whichplan--;
+ }
+
+ /* If non-partial, immediately mark as finished. */
+ if (node->as_whichplan < node->as_first_partial_plan)
+ node->as_pstate->pa_finished[node->as_whichplan] = true;
+
+ LWLockRelease(&pstate->pa_lock);
+
+ return true;
+}
+
+/* ----------------------------------------------------------------
+ * choose_next_subplan_for_worker
+ *
+ * Choose next subplan for a parallel-aware Append, returning
+ * false if there are no more.
+ *
+ * We start from the first plan and advance through the list;
+ * when we get back to the end, we loop back to the first
+ * partial plan. This assigns the non-partial plans first in
+ * order of descending cost and then spreads out the workers
+ * as evenly as possible across the remaining partial plans.
+ * ----------------------------------------------------------------
+ */
+static bool
+choose_next_subplan_for_worker(AppendState *node)
+{
+ ParallelAppendState *pstate = node->as_pstate;
+
+ /* Backward scan is not supported by parallel-aware plans */
+ Assert(ScanDirectionIsForward(node->ps.state->es_direction));
+
+ /* We should never be called when there are no subplans */
+ Assert(node->as_nplans > 0);
+
+ LWLockAcquire(&pstate->pa_lock, LW_EXCLUSIVE);
+
+ /* Mark just-completed subplan as finished. */
+ if (node->as_whichplan != INVALID_SUBPLAN_INDEX)
+ node->as_pstate->pa_finished[node->as_whichplan] = true;
+
+ /*
+ * If we've yet to determine the valid subplans then do so now. If
+ * run-time pruning is disabled then the valid subplans will always be set
+ * to all subplans.
+ */
+ else if (node->as_valid_subplans == NULL)
+ {
+ node->as_valid_subplans =
+ ExecFindMatchingSubPlans(node->as_prune_state);
+ mark_invalid_subplans_as_finished(node);
+ }
+
+ /* If all the plans are already done, we have nothing to do */
+ if (pstate->pa_next_plan == INVALID_SUBPLAN_INDEX)
+ {
+ LWLockRelease(&pstate->pa_lock);
+ return false;
+ }
+
+ /* Save the plan from which we are starting the search. */
+ node->as_whichplan = pstate->pa_next_plan;
+
+ /* Loop until we find a valid subplan to execute. */
+ while (pstate->pa_finished[pstate->pa_next_plan])
+ {
+ int nextplan;
+
+ nextplan = bms_next_member(node->as_valid_subplans,
+ pstate->pa_next_plan);
+ if (nextplan >= 0)
+ {
+ /* Advance to the next valid plan. */
+ pstate->pa_next_plan = nextplan;
+ }
+ else if (node->as_whichplan > node->as_first_partial_plan)
+ {
+ /*
+ * Try looping back to the first valid partial plan, if there is
+ * one. If there isn't, arrange to bail out below.
+ */
+ nextplan = bms_next_member(node->as_valid_subplans,
+ node->as_first_partial_plan - 1);
+ pstate->pa_next_plan =
+ nextplan < 0 ? node->as_whichplan : nextplan;
+ }
+ else
+ {
+ /*
+ * At last plan, and either there are no partial plans or we've
+ * tried them all. Arrange to bail out.
+ */
+ pstate->pa_next_plan = node->as_whichplan;
+ }
+
+ if (pstate->pa_next_plan == node->as_whichplan)
+ {
+ /* We've tried everything! */
+ pstate->pa_next_plan = INVALID_SUBPLAN_INDEX;
+ LWLockRelease(&pstate->pa_lock);
+ return false;
+ }
+ }
+
+ /* Pick the plan we found, and advance pa_next_plan one more time. */
+ node->as_whichplan = pstate->pa_next_plan;
+ pstate->pa_next_plan = bms_next_member(node->as_valid_subplans,
+ pstate->pa_next_plan);
+
+ /*
+ * If there are no more valid plans then try setting the next plan to the
+ * first valid partial plan.
+ */
+ if (pstate->pa_next_plan < 0)
+ {
+ int nextplan = bms_next_member(node->as_valid_subplans,
+ node->as_first_partial_plan - 1);
+
+ if (nextplan >= 0)
+ pstate->pa_next_plan = nextplan;
+ else
+ {
+ /*
+ * There are no valid partial plans, and we already chose the last
+ * non-partial plan; so flag that there's nothing more for our
+ * fellow workers to do.
+ */
+ pstate->pa_next_plan = INVALID_SUBPLAN_INDEX;
+ }
+ }
+
+ /* If non-partial, immediately mark as finished. */
+ if (node->as_whichplan < node->as_first_partial_plan)
+ node->as_pstate->pa_finished[node->as_whichplan] = true;
+
+ LWLockRelease(&pstate->pa_lock);
+
+ return true;
+}
+
+/*
+ * mark_invalid_subplans_as_finished
+ * Marks the ParallelAppendState's pa_finished as true for each invalid
+ * subplan.
+ *
+ * This function should only be called for parallel Append with run-time
+ * pruning enabled.
+ */
+static void
+mark_invalid_subplans_as_finished(AppendState *node)
+{
+ int i;
+
+ /* Only valid to call this while in parallel Append mode */
+ Assert(node->as_pstate);
+
+ /* Shouldn't have been called when run-time pruning is not enabled */
+ Assert(node->as_prune_state);
+
+ /* Nothing to do if all plans are valid */
+ if (bms_num_members(node->as_valid_subplans) == node->as_nplans)
+ return;
+
+ /* Mark all non-valid plans as finished */
+ for (i = 0; i < node->as_nplans; i++)
+ {
+ if (!bms_is_member(i, node->as_valid_subplans))
+ node->as_pstate->pa_finished[i] = true;
+ }
+}
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