granicus.if.org Git - postgresql/blob - src/backend/executor/nodeAppend.c

   1 /*-------------------------------------------------------------------------
   2  *
   3  * nodeAppend.c
   4  *        routines to handle append nodes.
   5  *
   6  * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
   7  * Portions Copyright (c) 1994, Regents of the University of California
   8  *
   9  *
  10  * IDENTIFICATION
  11  *        src/backend/executor/nodeAppend.c
  12  *
  13  *-------------------------------------------------------------------------
  14  */
  15 /* INTERFACE ROUTINES
  16  *              ExecInitAppend  - initialize the append node
  17  *              ExecAppend              - retrieve the next tuple from the node
  18  *              ExecEndAppend   - shut down the append node
  19  *              ExecReScanAppend - rescan the append node
  20  *
  21  *       NOTES
  22  *              Each append node contains a list of one or more subplans which
  23  *              must be iteratively processed (forwards or backwards).
  24  *              Tuples are retrieved by executing the 'whichplan'th subplan
  25  *              until the subplan stops returning tuples, at which point that
  26  *              plan is shut down and the next started up.
  27  *
  28  *              Append nodes don't make use of their left and right
  29  *              subtrees, rather they maintain a list of subplans so
  30  *              a typical append node looks like this in the plan tree:
  31  *
  32  *                                 ...
  33  *                                 /
  34  *                              Append -------+------+------+--- nil
  35  *                              /       \                 |              |              |
  36  *                        nil   nil              ...    ...    ...
  37  *                                                               subplans
  38  *
  39  *              Append nodes are currently used for unions, and to support
  40  *              inheritance queries, where several relations need to be scanned.
  41  *              For example, in our standard person/student/employee/student-emp
  42  *              example, where student and employee inherit from person
  43  *              and student-emp inherits from student and employee, the
  44  *              query:
  45  *
  46  *                              select name from person
  47  *
  48  *              generates the plan:
  49  *
  50  *                                |
  51  *                              Append -------+-------+--------+--------+
  52  *                              /       \                 |               |                |            |
  53  *                        nil   nil              Scan    Scan     Scan     Scan
  54  *                                                        |               |                |            |
  55  *                                                      person employee student student-emp
  56  */
  57
  58 #include "postgres.h"
  59
  60 #include "executor/execdebug.h"
  61 #include "executor/nodeAppend.h"
  62
  63 static bool exec_append_initialize_next(AppendState *appendstate);
  64
  65
  66 /* ----------------------------------------------------------------
  67  *              exec_append_initialize_next
  68  *
  69  *              Sets up the append state node for the "next" scan.
  70  *
  71  *              Returns t iff there is a "next" scan to process.
  72  * ----------------------------------------------------------------
  73  */
  74 static bool
  75 exec_append_initialize_next(AppendState *appendstate)
  76 {
  77         int                     whichplan;
  78
  79         /*
  80          * get information from the append node
  81          */
  82         whichplan = appendstate->as_whichplan;
  83
  84         if (whichplan < 0)
  85         {
  86                 /*
  87                  * if scanning in reverse, we start at the last scan in the list and
  88                  * then proceed back to the first.. in any case we inform ExecAppend
  89                  * that we are at the end of the line by returning FALSE
  90                  */
  91                 appendstate->as_whichplan = 0;
  92                 return FALSE;
  93         }
  94         else if (whichplan >= appendstate->as_nplans)
  95         {
  96                 /*
  97                  * as above, end the scan if we go beyond the last scan in our list..
  98                  */
  99                 appendstate->as_whichplan = appendstate->as_nplans - 1;
 100                 return FALSE;
 101         }
 102         else
 103         {
 104                 return TRUE;
 105         }
 106 }
 107
 108 /* ----------------------------------------------------------------
 109  *              ExecInitAppend
 110  *
 111  *              Begin all of the subscans of the append node.
 112  *
 113  *         (This is potentially wasteful, since the entire result of the
 114  *              append node may not be scanned, but this way all of the
 115  *              structures get allocated in the executor's top level memory
 116  *              block instead of that of the call to ExecAppend.)
 117  * ----------------------------------------------------------------
 118  */
 119 AppendState *
 120 ExecInitAppend(Append *node, EState *estate, int eflags)
 121 {
 122         AppendState *appendstate = makeNode(AppendState);
 123         PlanState **appendplanstates;
 124         int                     nplans;
 125         int                     i;
 126         ListCell   *lc;
 127
 128         /* check for unsupported flags */
 129         Assert(!(eflags & EXEC_FLAG_MARK));
 130
 131         /*
 132          * Set up empty vector of subplan states
 133          */
 134         nplans = list_length(node->appendplans);
 135
 136         appendplanstates = (PlanState **) palloc0(nplans * sizeof(PlanState *));
 137
 138         /*
 139          * create new AppendState for our append node
 140          */
 141         appendstate->ps.plan = (Plan *) node;
 142         appendstate->ps.state = estate;
 143         appendstate->appendplans = appendplanstates;
 144         appendstate->as_nplans = nplans;
 145
 146         /*
 147          * Miscellaneous initialization
 148          *
 149          * Append plans don't have expression contexts because they never call
 150          * ExecQual or ExecProject.
 151          */
 152
 153         /*
 154          * append nodes still have Result slots, which hold pointers to tuples, so
 155          * we have to initialize them.
 156          */
 157         ExecInitResultTupleSlot(estate, &appendstate->ps);
 158
 159         /*
 160          * call ExecInitNode on each of the plans to be executed and save the
 161          * results into the array "appendplans".
 162          */
 163         i = 0;
 164         foreach(lc, node->appendplans)
 165         {
 166                 Plan       *initNode = (Plan *) lfirst(lc);
 167
 168                 appendplanstates[i] = ExecInitNode(initNode, estate, eflags);
 169                 i++;
 170         }
 171
 172         /*
 173          * initialize output tuple type
 174          */
 175         ExecAssignResultTypeFromTL(&appendstate->ps);
 176         appendstate->ps.ps_ProjInfo = NULL;
 177
 178         /*
 179          * initialize to scan first subplan
 180          */
 181         appendstate->as_whichplan = 0;
 182         exec_append_initialize_next(appendstate);
 183
 184         return appendstate;
 185 }
 186
 187 /* ----------------------------------------------------------------
 188  *         ExecAppend
 189  *
 190  *              Handles iteration over multiple subplans.
 191  * ----------------------------------------------------------------
 192  */
 193 TupleTableSlot *
 194 ExecAppend(AppendState *node)
 195 {
 196         for (;;)
 197         {
 198                 PlanState  *subnode;
 199                 TupleTableSlot *result;
 200
 201                 /*
 202                  * figure out which subplan we are currently processing
 203                  */
 204                 subnode = node->appendplans[node->as_whichplan];
 205
 206                 /*
 207                  * get a tuple from the subplan
 208                  */
 209                 result = ExecProcNode(subnode);
 210
 211                 if (!TupIsNull(result))
 212                 {
 213                         /*
 214                          * If the subplan gave us something then return it as-is. We do
 215                          * NOT make use of the result slot that was set up in
 216                          * ExecInitAppend; there's no need for it.
 217                          */
 218                         return result;
 219                 }
 220
 221                 /*
 222                  * Go on to the "next" subplan in the appropriate direction. If no
 223                  * more subplans, return the empty slot set up for us by
 224                  * ExecInitAppend.
 225                  */
 226                 if (ScanDirectionIsForward(node->ps.state->es_direction))
 227                         node->as_whichplan++;
 228                 else
 229                         node->as_whichplan--;
 230                 if (!exec_append_initialize_next(node))
 231                         return ExecClearTuple(node->ps.ps_ResultTupleSlot);
 232
 233                 /* Else loop back and try to get a tuple from the new subplan */
 234         }
 235 }
 236
 237 /* ----------------------------------------------------------------
 238  *              ExecEndAppend
 239  *
 240  *              Shuts down the subscans of the append node.
 241  *
 242  *              Returns nothing of interest.
 243  * ----------------------------------------------------------------
 244  */
 245 void
 246 ExecEndAppend(AppendState *node)
 247 {
 248         PlanState **appendplans;
 249         int                     nplans;
 250         int                     i;
 251
 252         /*
 253          * get information from the node
 254          */
 255         appendplans = node->appendplans;
 256         nplans = node->as_nplans;
 257
 258         /*
 259          * shut down each of the subscans
 260          */
 261         for (i = 0; i < nplans; i++)
 262                 ExecEndNode(appendplans[i]);
 263 }
 264
 265 void
 266 ExecReScanAppend(AppendState *node)
 267 {
 268         int                     i;
 269
 270         for (i = 0; i < node->as_nplans; i++)
 271         {
 272                 PlanState  *subnode = node->appendplans[i];
 273
 274                 /*
 275                  * ExecReScan doesn't know about my subplans, so I have to do
 276                  * changed-parameter signaling myself.
 277                  */
 278                 if (node->ps.chgParam != NULL)
 279                         UpdateChangedParamSet(subnode, node->ps.chgParam);
 280
 281                 /*
 282                  * If chgParam of subnode is not null then plan will be re-scanned by
 283                  * first ExecProcNode.
 284                  */
 285                 if (subnode->chgParam == NULL)
 286                         ExecReScan(subnode);
 287         }
 288         node->as_whichplan = 0;
 289         exec_append_initialize_next(node);
 290 }