LCOV - code coverage report
Current view: top level - src/backend/executor - execScan.c (source / functions) Hit Total Coverage
Test: PostgreSQL 13devel Lines: 65 80 81.2 %
Date: 2019-09-19 02:07:14 Functions: 5 5 100.0 %
Legend: Lines: hit not hit

          Line data    Source code
       1             : /*-------------------------------------------------------------------------
       2             :  *
       3             :  * execScan.c
       4             :  *    This code provides support for generalized relation scans. ExecScan
       5             :  *    is passed a node and a pointer to a function to "do the right thing"
       6             :  *    and return a tuple from the relation. ExecScan then does the tedious
       7             :  *    stuff - checking the qualification and projecting the tuple
       8             :  *    appropriately.
       9             :  *
      10             :  * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
      11             :  * Portions Copyright (c) 1994, Regents of the University of California
      12             :  *
      13             :  *
      14             :  * IDENTIFICATION
      15             :  *    src/backend/executor/execScan.c
      16             :  *
      17             :  *-------------------------------------------------------------------------
      18             :  */
      19             : #include "postgres.h"
      20             : 
      21             : #include "executor/executor.h"
      22             : #include "miscadmin.h"
      23             : #include "utils/memutils.h"
      24             : 
      25             : 
      26             : 
      27             : /*
      28             :  * ExecScanFetch -- check interrupts & fetch next potential tuple
      29             :  *
      30             :  * This routine is concerned with substituting a test tuple if we are
      31             :  * inside an EvalPlanQual recheck.  If we aren't, just execute
      32             :  * the access method's next-tuple routine.
      33             :  */
      34             : static inline TupleTableSlot *
      35    68263120 : ExecScanFetch(ScanState *node,
      36             :               ExecScanAccessMtd accessMtd,
      37             :               ExecScanRecheckMtd recheckMtd)
      38             : {
      39    68263120 :     EState     *estate = node->ps.state;
      40             : 
      41    68263120 :     CHECK_FOR_INTERRUPTS();
      42             : 
      43    68263120 :     if (estate->es_epq_active != NULL)
      44             :     {
      45         202 :         EPQState   *epqstate = estate->es_epq_active;
      46             : 
      47             :         /*
      48             :          * We are inside an EvalPlanQual recheck.  Return the test tuple if
      49             :          * one is available, after rechecking any access-method-specific
      50             :          * conditions.
      51             :          */
      52         202 :         Index       scanrelid = ((Scan *) node->ps.plan)->scanrelid;
      53             : 
      54         202 :         if (scanrelid == 0)
      55             :         {
      56             :             /*
      57             :              * This is a ForeignScan or CustomScan which has pushed down a
      58             :              * join to the remote side.  The recheck method is responsible not
      59             :              * only for rechecking the scan/join quals but also for storing
      60             :              * the correct tuple in the slot.
      61             :              */
      62             : 
      63           0 :             TupleTableSlot *slot = node->ss_ScanTupleSlot;
      64             : 
      65           0 :             if (!(*recheckMtd) (node, slot))
      66           0 :                 ExecClearTuple(slot);   /* would not be returned by scan */
      67           0 :             return slot;
      68             :         }
      69         202 :         else if (epqstate->relsubs_done[scanrelid - 1])
      70             :         {
      71             :             /*
      72             :              * Return empty slot, as we already performed an EPQ substitution
      73             :              * for this relation.
      74             :              */
      75             : 
      76          30 :             TupleTableSlot *slot = node->ss_ScanTupleSlot;
      77             : 
      78             :             /* Return empty slot, as we already returned a tuple */
      79          30 :             return ExecClearTuple(slot);
      80             :         }
      81         172 :         else if (epqstate->relsubs_slot[scanrelid - 1] != NULL)
      82             :         {
      83             :             /*
      84             :              * Return replacement tuple provided by the EPQ caller.
      85             :              */
      86             : 
      87         148 :             TupleTableSlot *slot = epqstate->relsubs_slot[scanrelid - 1];
      88             : 
      89             :             Assert(epqstate->relsubs_rowmark[scanrelid - 1] == NULL);
      90             : 
      91             :             /* Mark to remember that we shouldn't return more */
      92         148 :             epqstate->relsubs_done[scanrelid - 1] = true;
      93             : 
      94             :             /* Return empty slot if we haven't got a test tuple */
      95         148 :             if (TupIsNull(slot))
      96           6 :                 return NULL;
      97             : 
      98             :             /* Check if it meets the access-method conditions */
      99         142 :             if (!(*recheckMtd) (node, slot))
     100           4 :                 return ExecClearTuple(slot);    /* would not be returned by
     101             :                                                  * scan */
     102         138 :             return slot;
     103             :         }
     104          24 :         else if (epqstate->relsubs_rowmark[scanrelid - 1] != NULL)
     105             :         {
     106             :             /*
     107             :              * Fetch and return replacement tuple using a non-locking rowmark.
     108             :              */
     109             : 
     110          14 :             TupleTableSlot *slot = node->ss_ScanTupleSlot;
     111             : 
     112             :             /* Mark to remember that we shouldn't return more */
     113          14 :             epqstate->relsubs_done[scanrelid - 1] = true;
     114             : 
     115          14 :             if (!EvalPlanQualFetchRowMark(epqstate, scanrelid, slot))
     116           0 :                 return NULL;
     117             : 
     118             :             /* Return empty slot if we haven't got a test tuple */
     119          14 :             if (TupIsNull(slot))
     120           0 :                 return NULL;
     121             : 
     122             :             /* Check if it meets the access-method conditions */
     123          14 :             if (!(*recheckMtd) (node, slot))
     124           0 :                 return ExecClearTuple(slot);    /* would not be returned by
     125             :                                                  * scan */
     126          14 :             return slot;
     127             :         }
     128             :     }
     129             : 
     130             :     /*
     131             :      * Run the node-type-specific access method function to get the next tuple
     132             :      */
     133    68262928 :     return (*accessMtd) (node);
     134             : }
     135             : 
     136             : /* ----------------------------------------------------------------
     137             :  *      ExecScan
     138             :  *
     139             :  *      Scans the relation using the 'access method' indicated and
     140             :  *      returns the next qualifying tuple.
     141             :  *      The access method returns the next tuple and ExecScan() is
     142             :  *      responsible for checking the tuple returned against the qual-clause.
     143             :  *
     144             :  *      A 'recheck method' must also be provided that can check an
     145             :  *      arbitrary tuple of the relation against any qual conditions
     146             :  *      that are implemented internal to the access method.
     147             :  *
     148             :  *      Conditions:
     149             :  *        -- the "cursor" maintained by the AMI is positioned at the tuple
     150             :  *           returned previously.
     151             :  *
     152             :  *      Initial States:
     153             :  *        -- the relation indicated is opened for scanning so that the
     154             :  *           "cursor" is positioned before the first qualifying tuple.
     155             :  * ----------------------------------------------------------------
     156             :  */
     157             : TupleTableSlot *
     158    46488068 : ExecScan(ScanState *node,
     159             :          ExecScanAccessMtd accessMtd,   /* function returning a tuple */
     160             :          ExecScanRecheckMtd recheckMtd)
     161             : {
     162             :     ExprContext *econtext;
     163             :     ExprState  *qual;
     164             :     ProjectionInfo *projInfo;
     165             : 
     166             :     /*
     167             :      * Fetch data from node
     168             :      */
     169    46488068 :     qual = node->ps.qual;
     170    46488068 :     projInfo = node->ps.ps_ProjInfo;
     171    46488068 :     econtext = node->ps.ps_ExprContext;
     172             : 
     173             :     /* interrupt checks are in ExecScanFetch */
     174             : 
     175             :     /*
     176             :      * If we have neither a qual to check nor a projection to do, just skip
     177             :      * all the overhead and return the raw scan tuple.
     178             :      */
     179    46488068 :     if (!qual && !projInfo)
     180             :     {
     181    15753512 :         ResetExprContext(econtext);
     182    15753512 :         return ExecScanFetch(node, accessMtd, recheckMtd);
     183             :     }
     184             : 
     185             :     /*
     186             :      * Reset per-tuple memory context to free any expression evaluation
     187             :      * storage allocated in the previous tuple cycle.
     188             :      */
     189    30734556 :     ResetExprContext(econtext);
     190             : 
     191             :     /*
     192             :      * get a tuple from the access method.  Loop until we obtain a tuple that
     193             :      * passes the qualification.
     194             :      */
     195             :     for (;;)
     196    21775052 :     {
     197             :         TupleTableSlot *slot;
     198             : 
     199    52509608 :         slot = ExecScanFetch(node, accessMtd, recheckMtd);
     200             : 
     201             :         /*
     202             :          * if the slot returned by the accessMtd contains NULL, then it means
     203             :          * there is nothing more to scan so we just return an empty slot,
     204             :          * being careful to use the projection result slot so it has correct
     205             :          * tupleDesc.
     206             :          */
     207    52509270 :         if (TupIsNull(slot))
     208             :         {
     209     1101690 :             if (projInfo)
     210     1058590 :                 return ExecClearTuple(projInfo->pi_state.resultslot);
     211             :             else
     212       43100 :                 return slot;
     213             :         }
     214             : 
     215             :         /*
     216             :          * place the current tuple into the expr context
     217             :          */
     218    51407580 :         econtext->ecxt_scantuple = slot;
     219             : 
     220             :         /*
     221             :          * check that the current tuple satisfies the qual-clause
     222             :          *
     223             :          * check for non-null qual here to avoid a function call to ExecQual()
     224             :          * when the qual is null ... saves only a few cycles, but they add up
     225             :          * ...
     226             :          */
     227    51407580 :         if (qual == NULL || ExecQual(qual, econtext))
     228             :         {
     229             :             /*
     230             :              * Found a satisfactory scan tuple.
     231             :              */
     232    29632510 :             if (projInfo)
     233             :             {
     234             :                 /*
     235             :                  * Form a projection tuple, store it in the result tuple slot
     236             :                  * and return it.
     237             :                  */
     238    27500206 :                 return ExecProject(projInfo);
     239             :             }
     240             :             else
     241             :             {
     242             :                 /*
     243             :                  * Here, we aren't projecting, so just return scan tuple.
     244             :                  */
     245     2132304 :                 return slot;
     246             :             }
     247             :         }
     248             :         else
     249    21775052 :             InstrCountFiltered1(node, 1);
     250             : 
     251             :         /*
     252             :          * Tuple fails qual, so free per-tuple memory and try again.
     253             :          */
     254    21775052 :         ResetExprContext(econtext);
     255             :     }
     256             : }
     257             : 
     258             : /*
     259             :  * ExecAssignScanProjectionInfo
     260             :  *      Set up projection info for a scan node, if necessary.
     261             :  *
     262             :  * We can avoid a projection step if the requested tlist exactly matches
     263             :  * the underlying tuple type.  If so, we just set ps_ProjInfo to NULL.
     264             :  * Note that this case occurs not only for simple "SELECT * FROM ...", but
     265             :  * also in most cases where there are joins or other processing nodes above
     266             :  * the scan node, because the planner will preferentially generate a matching
     267             :  * tlist.
     268             :  *
     269             :  * The scan slot's descriptor must have been set already.
     270             :  */
     271             : void
     272      258884 : ExecAssignScanProjectionInfo(ScanState *node)
     273             : {
     274      258884 :     Scan       *scan = (Scan *) node->ps.plan;
     275      258884 :     TupleDesc   tupdesc = node->ss_ScanTupleSlot->tts_tupleDescriptor;
     276             : 
     277      258884 :     ExecConditionalAssignProjectionInfo(&node->ps, tupdesc, scan->scanrelid);
     278      258884 : }
     279             : 
     280             : /*
     281             :  * ExecAssignScanProjectionInfoWithVarno
     282             :  *      As above, but caller can specify varno expected in Vars in the tlist.
     283             :  */
     284             : void
     285        9942 : ExecAssignScanProjectionInfoWithVarno(ScanState *node, Index varno)
     286             : {
     287        9942 :     TupleDesc   tupdesc = node->ss_ScanTupleSlot->tts_tupleDescriptor;
     288             : 
     289        9942 :     ExecConditionalAssignProjectionInfo(&node->ps, tupdesc, varno);
     290        9942 : }
     291             : 
     292             : /*
     293             :  * ExecScanReScan
     294             :  *
     295             :  * This must be called within the ReScan function of any plan node type
     296             :  * that uses ExecScan().
     297             :  */
     298             : void
     299     2494154 : ExecScanReScan(ScanState *node)
     300             : {
     301     2494154 :     EState     *estate = node->ps.state;
     302             : 
     303             :     /*
     304             :      * We must clear the scan tuple so that observers (e.g., execCurrent.c)
     305             :      * can tell that this plan node is not positioned on a tuple.
     306             :      */
     307     2494154 :     ExecClearTuple(node->ss_ScanTupleSlot);
     308             : 
     309             :     /* Rescan EvalPlanQual tuple if we're inside an EvalPlanQual recheck */
     310     2494154 :     if (estate->es_epq_active != NULL)
     311             :     {
     312          30 :         EPQState   *epqstate = estate->es_epq_active;
     313          30 :         Index       scanrelid = ((Scan *) node->ps.plan)->scanrelid;
     314             : 
     315          30 :         if (scanrelid > 0)
     316          30 :             epqstate->relsubs_done[scanrelid - 1] = false;
     317             :         else
     318             :         {
     319             :             Bitmapset  *relids;
     320           0 :             int         rtindex = -1;
     321             : 
     322             :             /*
     323             :              * If an FDW or custom scan provider has replaced the join with a
     324             :              * scan, there are multiple RTIs; reset the epqScanDone flag for
     325             :              * all of them.
     326             :              */
     327           0 :             if (IsA(node->ps.plan, ForeignScan))
     328           0 :                 relids = ((ForeignScan *) node->ps.plan)->fs_relids;
     329           0 :             else if (IsA(node->ps.plan, CustomScan))
     330           0 :                 relids = ((CustomScan *) node->ps.plan)->custom_relids;
     331             :             else
     332           0 :                 elog(ERROR, "unexpected scan node: %d",
     333             :                      (int) nodeTag(node->ps.plan));
     334             : 
     335           0 :             while ((rtindex = bms_next_member(relids, rtindex)) >= 0)
     336             :             {
     337             :                 Assert(rtindex > 0);
     338           0 :                 epqstate->relsubs_done[rtindex - 1] = false;
     339             :             }
     340             :         }
     341             :     }
     342     2494154 : }

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