nodeTidrangescan.c

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * nodeTidrangescan.c
 *    Routines to support TID range scans of relations
 *
 * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/executor/nodeTidrangescan.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include "access/relscan.h"
#include "access/sysattr.h"
#include "access/tableam.h"
#include "catalog/pg_operator.h"
#include "executor/execdebug.h"
#include "executor/nodeTidrangescan.h"
#include "nodes/nodeFuncs.h"
#include "storage/bufmgr.h"
#include "utils/rel.h"
 
 
/*
 * It's sufficient to check varattno to identify the CTID variable, as any
 * Var in the relation scan qual must be for our table.  (Even if it's a
 * parameterized scan referencing some other table's CTID, the other table's
 * Var would have become a Param by the time it gets here.)
 */
#define IsCTIDVar(node)  \
    ((node) != NULL && \
     IsA((node), Var) && \
     ((Var *) (node))->varattno == SelfItemPointerAttributeNumber)
 
typedef enum
{
    TIDEXPR_UPPER_BOUND,
    TIDEXPR_LOWER_BOUND
} TidExprType;
 
/* Upper or lower range bound for scan */
typedef struct TidOpExpr
{
    TidExprType exprtype;       /* type of op; lower or upper */
    ExprState  *exprstate;      /* ExprState for a TID-yielding subexpr */
    bool        inclusive;      /* whether op is inclusive */
} TidOpExpr;
 
/*
 * For the given 'expr', build and return an appropriate TidOpExpr taking into
 * account the expr's operator and operand order.
 */
static TidOpExpr *
MakeTidOpExpr(OpExpr *expr, TidRangeScanState *tidstate)
{
    Node       *arg1 = get_leftop((Expr *) expr);
    Node       *arg2 = get_rightop((Expr *) expr);
    ExprState  *exprstate = NULL;
    bool        invert = false;
    TidOpExpr  *tidopexpr;
 
    if (IsCTIDVar(arg1))
        exprstate = ExecInitExpr((Expr *) arg2, &tidstate->ss.ps);
    else if (IsCTIDVar(arg2))
    {
        exprstate = ExecInitExpr((Expr *) arg1, &tidstate->ss.ps);
        invert = true;
    }
    else
        elog(ERROR, "could not identify CTID variable");
 
    tidopexpr = (TidOpExpr *) palloc(sizeof(TidOpExpr));
    tidopexpr->inclusive = false;   /* for now */
 
    switch (expr->opno)
    {
        case TIDLessEqOperator:
            tidopexpr->inclusive = true;
            /* fall through */
        case TIDLessOperator:
            tidopexpr->exprtype = invert ? TIDEXPR_LOWER_BOUND : TIDEXPR_UPPER_BOUND;
            break;
        case TIDGreaterEqOperator:
            tidopexpr->inclusive = true;
            /* fall through */
        case TIDGreaterOperator:
            tidopexpr->exprtype = invert ? TIDEXPR_UPPER_BOUND : TIDEXPR_LOWER_BOUND;
            break;
        default:
            elog(ERROR, "could not identify CTID operator");
    }
 
    tidopexpr->exprstate = exprstate;
 
    return tidopexpr;
}
 
/*
 * Extract the qual subexpressions that yield TIDs to search for,
 * and compile them into ExprStates if they're ordinary expressions.
 */
static void
TidExprListCreate(TidRangeScanState *tidrangestate)
{
    TidRangeScan *node = (TidRangeScan *) tidrangestate->ss.ps.plan;
    List       *tidexprs = NIL;
    ListCell   *l;
 
    foreach(l, node->tidrangequals)
    {
        OpExpr     *opexpr = lfirst(l);
        TidOpExpr  *tidopexpr;
 
        if (!IsA(opexpr, OpExpr))
            elog(ERROR, "could not identify CTID expression");
 
        tidopexpr = MakeTidOpExpr(opexpr, tidrangestate);
        tidexprs = lappend(tidexprs, tidopexpr);
    }
 
    tidrangestate->trss_tidexprs = tidexprs;
}
 
/* ----------------------------------------------------------------
 *      TidRangeEval
 *
 *      Compute and set node's block and offset range to scan by evaluating
 *      the trss_tidexprs.  Returns false if we detect the range cannot
 *      contain any tuples.  Returns true if it's possible for the range to
 *      contain tuples.
 * ----------------------------------------------------------------
 */
static bool
TidRangeEval(TidRangeScanState *node)
{
    ExprContext *econtext = node->ss.ps.ps_ExprContext;
    ItemPointerData lowerBound;
    ItemPointerData upperBound;
    ListCell   *l;
 
    /*
     * Set the upper and lower bounds to the absolute limits of the range of
     * the ItemPointer type.  Below we'll try to narrow this range on either
     * side by looking at the TidOpExprs.
     */
    ItemPointerSet(&lowerBound, 0, 0);
    ItemPointerSet(&upperBound, InvalidBlockNumber, PG_UINT16_MAX);
 
    foreach(l, node->trss_tidexprs)
    {
        TidOpExpr  *tidopexpr = (TidOpExpr *) lfirst(l);
        ItemPointer itemptr;
        bool        isNull;
 
        /* Evaluate this bound. */
        itemptr = (ItemPointer)
            DatumGetPointer(ExecEvalExprSwitchContext(tidopexpr->exprstate,
                                                      econtext,
                                                      &isNull));
 
        /* If the bound is NULL, *nothing* matches the qual. */
        if (isNull)
            return false;
 
        if (tidopexpr->exprtype == TIDEXPR_LOWER_BOUND)
        {
            ItemPointerData lb;
 
            ItemPointerCopy(itemptr, &lb);
 
            /*
             * Normalize non-inclusive ranges to become inclusive.  The
             * resulting ItemPointer here may not be a valid item pointer.
             */
            if (!tidopexpr->inclusive)
                ItemPointerInc(&lb);
 
            /* Check if we can narrow the range using this qual */
            if (ItemPointerCompare(&lb, &lowerBound) > 0)
                ItemPointerCopy(&lb, &lowerBound);
        }
 
        else if (tidopexpr->exprtype == TIDEXPR_UPPER_BOUND)
        {
            ItemPointerData ub;
 
            ItemPointerCopy(itemptr, &ub);
 
            /*
             * Normalize non-inclusive ranges to become inclusive.  The
             * resulting ItemPointer here may not be a valid item pointer.
             */
            if (!tidopexpr->inclusive)
                ItemPointerDec(&ub);
 
            /* Check if we can narrow the range using this qual */
            if (ItemPointerCompare(&ub, &upperBound) < 0)
                ItemPointerCopy(&ub, &upperBound);
        }
    }
 
    ItemPointerCopy(&lowerBound, &node->trss_mintid);
    ItemPointerCopy(&upperBound, &node->trss_maxtid);
 
    return true;
}
 
/* ----------------------------------------------------------------
 *      TidRangeNext
 *
 *      Retrieve a tuple from the TidRangeScan node's currentRelation
 *      using the TIDs in the TidRangeScanState information.
 *
 * ----------------------------------------------------------------
 */
static TupleTableSlot *
TidRangeNext(TidRangeScanState *node)
{
    TableScanDesc scandesc;
    EState     *estate;
    ScanDirection direction;
    TupleTableSlot *slot;
 
    /*
     * extract necessary information from TID scan node
     */
    scandesc = node->ss.ss_currentScanDesc;
    estate = node->ss.ps.state;
    slot = node->ss.ss_ScanTupleSlot;
    direction = estate->es_direction;
 
    if (!node->trss_inScan)
    {
        /* First time through, compute TID range to scan */
        if (!TidRangeEval(node))
            return NULL;
 
        if (scandesc == NULL)
        {
            scandesc = table_beginscan_tidrange(node->ss.ss_currentRelation,
                                                estate->es_snapshot,
                                                &node->trss_mintid,
                                                &node->trss_maxtid);
            node->ss.ss_currentScanDesc = scandesc;
        }
        else
        {
            /* rescan with the updated TID range */
            table_rescan_tidrange(scandesc, &node->trss_mintid,
                                  &node->trss_maxtid);
        }
 
        node->trss_inScan = true;
    }
 
    /* Fetch the next tuple. */
    if (!table_scan_getnextslot_tidrange(scandesc, direction, slot))
    {
        node->trss_inScan = false;
        ExecClearTuple(slot);
    }
 
    return slot;
}
 
/*
 * TidRangeRecheck -- access method routine to recheck a tuple in EvalPlanQual
 */
static bool
TidRangeRecheck(TidRangeScanState *node, TupleTableSlot *slot)
{
    return true;
}
 
/* ----------------------------------------------------------------
 *      ExecTidRangeScan(node)
 *
 *      Scans the relation using tids and returns the next qualifying tuple.
 *      We call the ExecScan() routine and pass it the appropriate
 *      access method functions.
 *
 *      Conditions:
 *        -- the "cursor" maintained by the AMI is positioned at the tuple
 *           returned previously.
 *
 *      Initial States:
 *        -- the relation indicated is opened for TID range scanning.
 * ----------------------------------------------------------------
 */
static TupleTableSlot *
ExecTidRangeScan(PlanState *pstate)
{
    TidRangeScanState *node = castNode(TidRangeScanState, pstate);
 
    return ExecScan(&node->ss,
                    (ExecScanAccessMtd) TidRangeNext,
                    (ExecScanRecheckMtd) TidRangeRecheck);
}
 
/* ----------------------------------------------------------------
 *      ExecReScanTidRangeScan(node)
 * ----------------------------------------------------------------
 */
void
ExecReScanTidRangeScan(TidRangeScanState *node)
{
    /* mark scan as not in progress, and tid range list as not computed yet */
    node->trss_inScan = false;
 
    /*
     * We must wait until TidRangeNext before calling table_rescan_tidrange.
     */
    ExecScanReScan(&node->ss);
}
 
/* ----------------------------------------------------------------
 *      ExecEndTidRangeScan
 *
 *      Releases any storage allocated through C routines.
 *      Returns nothing.
 * ----------------------------------------------------------------
 */
void
ExecEndTidRangeScan(TidRangeScanState *node)
{
    TableScanDesc scan = node->ss.ss_currentScanDesc;
 
    if (scan != NULL)
        table_endscan(scan);
 
    /*
     * Free the exprcontext
     */
    ExecFreeExprContext(&node->ss.ps);
 
    /*
     * clear out tuple table slots
     */
    if (node->ss.ps.ps_ResultTupleSlot)
        ExecClearTuple(node->ss.ps.ps_ResultTupleSlot);
    ExecClearTuple(node->ss.ss_ScanTupleSlot);
}
 
/* ----------------------------------------------------------------
 *      ExecInitTidRangeScan
 *
 *      Initializes the tid range scan's state information, creates
 *      scan keys, and opens the scan relation.
 *
 *      Parameters:
 *        node: TidRangeScan node produced by the planner.
 *        estate: the execution state initialized in InitPlan.
 * ----------------------------------------------------------------
 */
TidRangeScanState *
ExecInitTidRangeScan(TidRangeScan *node, EState *estate, int eflags)
{
    TidRangeScanState *tidrangestate;
    Relation    currentRelation;
 
    /*
     * create state structure
     */
    tidrangestate = makeNode(TidRangeScanState);
    tidrangestate->ss.ps.plan = (Plan *) node;
    tidrangestate->ss.ps.state = estate;
    tidrangestate->ss.ps.ExecProcNode = ExecTidRangeScan;
 
    /*
     * Miscellaneous initialization
     *
     * create expression context for node
     */
    ExecAssignExprContext(estate, &tidrangestate->ss.ps);
 
    /*
     * mark scan as not in progress, and TID range as not computed yet
     */
    tidrangestate->trss_inScan = false;
 
    /*
     * open the scan relation
     */
    currentRelation = ExecOpenScanRelation(estate, node->scan.scanrelid, eflags);
 
    tidrangestate->ss.ss_currentRelation = currentRelation;
    tidrangestate->ss.ss_currentScanDesc = NULL;    /* no table scan here */
 
    /*
     * get the scan type from the relation descriptor.
     */
    ExecInitScanTupleSlot(estate, &tidrangestate->ss,
                          RelationGetDescr(currentRelation),
                          table_slot_callbacks(currentRelation));
 
    /*
     * Initialize result type and projection.
     */
    ExecInitResultTypeTL(&tidrangestate->ss.ps);
    ExecAssignScanProjectionInfo(&tidrangestate->ss);
 
    /*
     * initialize child expressions
     */
    tidrangestate->ss.ps.qual =
        ExecInitQual(node->scan.plan.qual, (PlanState *) tidrangestate);
 
    TidExprListCreate(tidrangestate);
 
    /*
     * all done.
     */
    return tidrangestate;
}