postgres/src/backend/executor/nodeSort.c

/*-------------------------------------------------------------------------
 *
 * nodeSort.c
 *	  Routines to handle sorting of relations.
 *
 * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  src/backend/executor/nodeSort.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "access/parallel.h"
#include "executor/execdebug.h"
#include "executor/nodeSort.h"
#include "miscadmin.h"
#include "utils/tuplesort.h"


/* ----------------------------------------------------------------
 *		ExecSort
 *
 *		Sorts tuples from the outer subtree of the node using tuplesort,
 *		which saves the results in a temporary file or memory. After the
 *		initial call, returns a tuple from the file with each call.
 *
 *		There are two distinct ways that this sort can be performed:
 *
 *		1) When the result is a single column we perform a Datum sort.
 *
 *		2) When the result contains multiple columns we perform a tuple sort.
 *
 *		We could do this by always performing a tuple sort, however sorting
 *		Datums only can be significantly faster than sorting tuples,
 *		especially when the Datums are of a pass-by-value type.
 *
 *		Conditions:
 *		  -- none.
 *
 *		Initial States:
 *		  -- the outer child is prepared to return the first tuple.
 * ----------------------------------------------------------------
 */
static TupleTableSlot *
ExecSort(PlanState *pstate)
{
	SortState  *node = castNode(SortState, pstate);
	EState	   *estate;
	ScanDirection dir;
	Tuplesortstate *tuplesortstate;
	TupleTableSlot *slot;

	CHECK_FOR_INTERRUPTS();

	/*
	 * get state info from node
	 */
	SO1_printf("ExecSort: %s\n",
			   "entering routine");

	estate = node->ss.ps.state;
	dir = estate->es_direction;
	tuplesortstate = (Tuplesortstate *) node->tuplesortstate;

	/*
	 * If first time through, read all tuples from outer plan and pass them to
	 * tuplesort.c. Subsequent calls just fetch tuples from tuplesort.
	 */

	if (!node->sort_Done)
	{
		Sort	   *plannode = (Sort *) node->ss.ps.plan;
		PlanState  *outerNode;
		TupleDesc	tupDesc;
		int			tuplesortopts = TUPLESORT_NONE;

		SO1_printf("ExecSort: %s\n",
				   "sorting subplan");

		/*
		 * Want to scan subplan in the forward direction while creating the
		 * sorted data.
		 */
		estate->es_direction = ForwardScanDirection;

		/*
		 * Initialize tuplesort module.
		 */
		SO1_printf("ExecSort: %s\n",
				   "calling tuplesort_begin");

		outerNode = outerPlanState(node);
		tupDesc = ExecGetResultType(outerNode);

		if (node->randomAccess)
			tuplesortopts |= TUPLESORT_RANDOMACCESS;
		if (node->bounded)
			tuplesortopts |= TUPLESORT_ALLOWBOUNDED;

		if (node->datumSort)
			tuplesortstate = tuplesort_begin_datum(TupleDescAttr(tupDesc, 0)->atttypid,
												   plannode->sortOperators[0],
												   plannode->collations[0],
												   plannode->nullsFirst[0],
												   work_mem,
												   NULL,
												   tuplesortopts);
		else
			tuplesortstate = tuplesort_begin_heap(tupDesc,
												  plannode->numCols,
												  plannode->sortColIdx,
												  plannode->sortOperators,
												  plannode->collations,
												  plannode->nullsFirst,
												  work_mem,
												  NULL,
												  tuplesortopts);
		if (node->bounded)
			tuplesort_set_bound(tuplesortstate, node->bound);
		node->tuplesortstate = (void *) tuplesortstate;

		/*
		 * Scan the subplan and feed all the tuples to tuplesort using the
		 * appropriate method based on the type of sort we're doing.
		 */
		if (node->datumSort)
		{
			for (;;)
			{
				slot = ExecProcNode(outerNode);

				if (TupIsNull(slot))
					break;
				slot_getsomeattrs(slot, 1);
				tuplesort_putdatum(tuplesortstate,
								   slot->tts_values[0],
								   slot->tts_isnull[0]);
			}
		}
		else
		{
			for (;;)
			{
				slot = ExecProcNode(outerNode);

				if (TupIsNull(slot))
					break;
				tuplesort_puttupleslot(tuplesortstate, slot);
			}
		}

		/*
		 * Complete the sort.
		 */
		tuplesort_performsort(tuplesortstate);

		/*
		 * restore to user specified direction
		 */
		estate->es_direction = dir;

		/*
		 * finally set the sorted flag to true
		 */
		node->sort_Done = true;
		node->bounded_Done = node->bounded;
		node->bound_Done = node->bound;
		if (node->shared_info && node->am_worker)
		{
			TuplesortInstrumentation *si;

			Assert(IsParallelWorker());
			Assert(ParallelWorkerNumber <= node->shared_info->num_workers);
			si = &node->shared_info->sinstrument[ParallelWorkerNumber];
			tuplesort_get_stats(tuplesortstate, si);
		}
		SO1_printf("ExecSort: %s\n", "sorting done");
	}

	SO1_printf("ExecSort: %s\n",
			   "retrieving tuple from tuplesort");

	slot = node->ss.ps.ps_ResultTupleSlot;

	/*
	 * Fetch the next sorted item from the appropriate tuplesort function. For
	 * datum sorts we must manage the slot ourselves and leave it clear when
	 * tuplesort_getdatum returns false to indicate there are no more datums.
	 * For tuple sorts, tuplesort_gettupleslot manages the slot for us and
	 * empties the slot when it runs out of tuples.
	 */
	if (node->datumSort)
	{
		ExecClearTuple(slot);
		if (tuplesort_getdatum(tuplesortstate, ScanDirectionIsForward(dir),
							   &(slot->tts_values[0]), &(slot->tts_isnull[0]), NULL))
			ExecStoreVirtualTuple(slot);
	}
	else
		(void) tuplesort_gettupleslot(tuplesortstate,
									  ScanDirectionIsForward(dir),
									  false, slot, NULL);

	return slot;
}

/* ----------------------------------------------------------------
 *		ExecInitSort
 *
 *		Creates the run-time state information for the sort node
 *		produced by the planner and initializes its outer subtree.
 * ----------------------------------------------------------------
 */
SortState *
ExecInitSort(Sort *node, EState *estate, int eflags)
{
	SortState  *sortstate;

	SO1_printf("ExecInitSort: %s\n",
			   "initializing sort node");

	/*
	 * create state structure
	 */
	sortstate = makeNode(SortState);
	sortstate->ss.ps.plan = (Plan *) node;
	sortstate->ss.ps.state = estate;
	sortstate->ss.ps.ExecProcNode = ExecSort;

	/*
	 * We must have random access to the sort output to do backward scan or
	 * mark/restore.  We also prefer to materialize the sort output if we
	 * might be called on to rewind and replay it many times.
	 */
	sortstate->randomAccess = (eflags & (EXEC_FLAG_REWIND |
										 EXEC_FLAG_BACKWARD |
										 EXEC_FLAG_MARK)) != 0;

	sortstate->bounded = false;
	sortstate->sort_Done = false;
	sortstate->tuplesortstate = NULL;

	/*
	 * Miscellaneous initialization
	 *
	 * Sort nodes don't initialize their ExprContexts because they never call
	 * ExecQual or ExecProject.
	 */

	/*
	 * initialize child nodes
	 *
	 * We shield the child node from the need to support REWIND, BACKWARD, or
	 * MARK/RESTORE.
	 */
	eflags &= ~(EXEC_FLAG_REWIND | EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK);

	outerPlanState(sortstate) = ExecInitNode(outerPlan(node), estate, eflags);

	/*
	 * Initialize scan slot and type.
	 */
	ExecCreateScanSlotFromOuterPlan(estate, &sortstate->ss, &TTSOpsVirtual);

	/*
	 * Initialize return slot and type. No need to initialize projection info
	 * because this node doesn't do projections.
	 */
	ExecInitResultTupleSlotTL(&sortstate->ss.ps, &TTSOpsMinimalTuple);
	sortstate->ss.ps.ps_ProjInfo = NULL;

	/*
	 * We perform a Datum sort when we're sorting just a single column,
	 * otherwise we perform a tuple sort.
	 */
	if (ExecGetResultType(outerPlanState(sortstate))->natts == 1)
		sortstate->datumSort = true;
	else
		sortstate->datumSort = false;

	SO1_printf("ExecInitSort: %s\n",
			   "sort node initialized");

	return sortstate;
}

/* ----------------------------------------------------------------
 *		ExecEndSort(node)
 * ----------------------------------------------------------------
 */
void
ExecEndSort(SortState *node)
{
	SO1_printf("ExecEndSort: %s\n",
			   "shutting down sort node");

	/*
	 * clean out the tuple table
	 */
	ExecClearTuple(node->ss.ss_ScanTupleSlot);
	/* must drop pointer to sort result tuple */
	ExecClearTuple(node->ss.ps.ps_ResultTupleSlot);

	/*
	 * Release tuplesort resources
	 */
	if (node->tuplesortstate != NULL)
		tuplesort_end((Tuplesortstate *) node->tuplesortstate);
	node->tuplesortstate = NULL;

	/*
	 * shut down the subplan
	 */
	ExecEndNode(outerPlanState(node));

	SO1_printf("ExecEndSort: %s\n",
			   "sort node shutdown");
}

/* ----------------------------------------------------------------
 *		ExecSortMarkPos
 *
 *		Calls tuplesort to save the current position in the sorted file.
 * ----------------------------------------------------------------
 */
void
ExecSortMarkPos(SortState *node)
{
	/*
	 * if we haven't sorted yet, just return
	 */
	if (!node->sort_Done)
		return;

	tuplesort_markpos((Tuplesortstate *) node->tuplesortstate);
}

/* ----------------------------------------------------------------
 *		ExecSortRestrPos
 *
 *		Calls tuplesort to restore the last saved sort file position.
 * ----------------------------------------------------------------
 */
void
ExecSortRestrPos(SortState *node)
{
	/*
	 * if we haven't sorted yet, just return.
	 */
	if (!node->sort_Done)
		return;

	/*
	 * restore the scan to the previously marked position
	 */
	tuplesort_restorepos((Tuplesortstate *) node->tuplesortstate);
}

void
ExecReScanSort(SortState *node)
{
	PlanState  *outerPlan = outerPlanState(node);

	/*
	 * If we haven't sorted yet, just return. If outerplan's chgParam is not
	 * NULL then it will be re-scanned by ExecProcNode, else no reason to
	 * re-scan it at all.
	 */
	if (!node->sort_Done)
		return;

	/* must drop pointer to sort result tuple */
	ExecClearTuple(node->ss.ps.ps_ResultTupleSlot);

	/*
	 * If subnode is to be rescanned then we forget previous sort results; we
	 * have to re-read the subplan and re-sort.  Also must re-sort if the
	 * bounded-sort parameters changed or we didn't select randomAccess.
	 *
	 * Otherwise we can just rewind and rescan the sorted output.
	 */
	if (outerPlan->chgParam != NULL ||
		node->bounded != node->bounded_Done ||
		node->bound != node->bound_Done ||
		!node->randomAccess)
	{
		node->sort_Done = false;
		tuplesort_end((Tuplesortstate *) node->tuplesortstate);
		node->tuplesortstate = NULL;

		/*
		 * if chgParam of subnode is not null then plan will be re-scanned by
		 * first ExecProcNode.
		 */
		if (outerPlan->chgParam == NULL)
			ExecReScan(outerPlan);
	}
	else
		tuplesort_rescan((Tuplesortstate *) node->tuplesortstate);
}

/* ----------------------------------------------------------------
 *						Parallel Query Support
 * ----------------------------------------------------------------
 */

/* ----------------------------------------------------------------
 *		ExecSortEstimate
 *
 *		Estimate space required to propagate sort statistics.
 * ----------------------------------------------------------------
 */
void
ExecSortEstimate(SortState *node, ParallelContext *pcxt)
{
	Size		size;

	/* don't need this if not instrumenting or no workers */
	if (!node->ss.ps.instrument || pcxt->nworkers == 0)
		return;

	size = mul_size(pcxt->nworkers, sizeof(TuplesortInstrumentation));
	size = add_size(size, offsetof(SharedSortInfo, sinstrument));
	shm_toc_estimate_chunk(&pcxt->estimator, size);
	shm_toc_estimate_keys(&pcxt->estimator, 1);
}

/* ----------------------------------------------------------------
 *		ExecSortInitializeDSM
 *
 *		Initialize DSM space for sort statistics.
 * ----------------------------------------------------------------
 */
void
ExecSortInitializeDSM(SortState *node, ParallelContext *pcxt)
{
	Size		size;

	/* don't need this if not instrumenting or no workers */
	if (!node->ss.ps.instrument || pcxt->nworkers == 0)
		return;

	size = offsetof(SharedSortInfo, sinstrument)
		+ pcxt->nworkers * sizeof(TuplesortInstrumentation);
	node->shared_info = shm_toc_allocate(pcxt->toc, size);
	/* ensure any unfilled slots will contain zeroes */
	memset(node->shared_info, 0, size);
	node->shared_info->num_workers = pcxt->nworkers;
	shm_toc_insert(pcxt->toc, node->ss.ps.plan->plan_node_id,
				   node->shared_info);
}

/* ----------------------------------------------------------------
 *		ExecSortInitializeWorker
 *
 *		Attach worker to DSM space for sort statistics.
 * ----------------------------------------------------------------
 */
void
ExecSortInitializeWorker(SortState *node, ParallelWorkerContext *pwcxt)
{
	node->shared_info =
		shm_toc_lookup(pwcxt->toc, node->ss.ps.plan->plan_node_id, true);
	node->am_worker = true;
}

/* ----------------------------------------------------------------
 *		ExecSortRetrieveInstrumentation
 *
 *		Transfer sort statistics from DSM to private memory.
 * ----------------------------------------------------------------
 */
void
ExecSortRetrieveInstrumentation(SortState *node)
{
	Size		size;
	SharedSortInfo *si;

	if (node->shared_info == NULL)
		return;

	size = offsetof(SharedSortInfo, sinstrument)
		+ node->shared_info->num_workers * sizeof(TuplesortInstrumentation);
	si = palloc(size);
	memcpy(si, node->shared_info, size);
	node->shared_info = si;
}