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) 1996-2017, 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 #include "miscadmin.h"
  63
  64 static bool exec_append_initialize_next(AppendState *appendstate);
  65
  66
  67 /* ----------------------------------------------------------------
  68  *              exec_append_initialize_next
  69  *
  70  *              Sets up the append state node for the "next" scan.
  71  *
  72  *              Returns t iff there is a "next" scan to process.
  73  * ----------------------------------------------------------------
  74  */
  75 static bool
  76 exec_append_initialize_next(AppendState *appendstate)
  77 {
  78         int                     whichplan;
  79
  80         /*
  81          * get information from the append node
  82          */
  83         whichplan = appendstate->as_whichplan;
  84
  85         if (whichplan < 0)
  86         {
  87                 /*
  88                  * if scanning in reverse, we start at the last scan in the list and
  89                  * then proceed back to the first.. in any case we inform ExecAppend
  90                  * that we are at the end of the line by returning FALSE
  91                  */
  92                 appendstate->as_whichplan = 0;
  93                 return FALSE;
  94         }
  95         else if (whichplan >= appendstate->as_nplans)
  96         {
  97                 /*
  98                  * as above, end the scan if we go beyond the last scan in our list..
  99                  */
 100                 appendstate->as_whichplan = appendstate->as_nplans - 1;
 101                 return FALSE;
 102         }
 103         else
 104         {
 105                 return TRUE;
 106         }
 107 }
 108
 109 /* ----------------------------------------------------------------
 110  *              ExecInitAppend
 111  *
 112  *              Begin all of the subscans of the append node.
 113  *
 114  *         (This is potentially wasteful, since the entire result of the
 115  *              append node may not be scanned, but this way all of the
 116  *              structures get allocated in the executor's top level memory
 117  *              block instead of that of the call to ExecAppend.)
 118  * ----------------------------------------------------------------
 119  */
 120 AppendState *
 121 ExecInitAppend(Append *node, EState *estate, int eflags)
 122 {
 123         AppendState *appendstate = makeNode(AppendState);
 124         PlanState **appendplanstates;
 125         int                     nplans;
 126         int                     i;
 127         ListCell   *lc;
 128
 129         /* check for unsupported flags */
 130         Assert(!(eflags & EXEC_FLAG_MARK));
 131
 132         /*
 133          * Lock the non-leaf tables in the partition tree controlled by this node.
 134          * It's a no-op for non-partitioned parent tables.
 135          */
 136         ExecLockNonLeafAppendTables(node->partitioned_rels, estate);
 137
 138         /*
 139          * Set up empty vector of subplan states
 140          */
 141         nplans = list_length(node->appendplans);
 142
 143         appendplanstates = (PlanState **) palloc0(nplans * sizeof(PlanState *));
 144
 145         /*
 146          * create new AppendState for our append node
 147          */
 148         appendstate->ps.plan = (Plan *) node;
 149         appendstate->ps.state = estate;
 150         appendstate->appendplans = appendplanstates;
 151         appendstate->as_nplans = nplans;
 152
 153         /*
 154          * Miscellaneous initialization
 155          *
 156          * Append plans don't have expression contexts because they never call
 157          * ExecQual or ExecProject.
 158          */
 159
 160         /*
 161          * append nodes still have Result slots, which hold pointers to tuples, so
 162          * we have to initialize them.
 163          */
 164         ExecInitResultTupleSlot(estate, &appendstate->ps);
 165
 166         /*
 167          * call ExecInitNode on each of the plans to be executed and save the
 168          * results into the array "appendplans".
 169          */
 170         i = 0;
 171         foreach(lc, node->appendplans)
 172         {
 173                 Plan       *initNode = (Plan *) lfirst(lc);
 174
 175                 appendplanstates[i] = ExecInitNode(initNode, estate, eflags);
 176                 i++;
 177         }
 178
 179         /*
 180          * initialize output tuple type
 181          */
 182         ExecAssignResultTypeFromTL(&appendstate->ps);
 183         appendstate->ps.ps_ProjInfo = NULL;
 184
 185         /*
 186          * initialize to scan first subplan
 187          */
 188         appendstate->as_whichplan = 0;
 189         exec_append_initialize_next(appendstate);
 190
 191         return appendstate;
 192 }
 193
 194 /* ----------------------------------------------------------------
 195  *         ExecAppend
 196  *
 197  *              Handles iteration over multiple subplans.
 198  * ----------------------------------------------------------------
 199  */
 200 TupleTableSlot *
 201 ExecAppend(AppendState *node)
 202 {
 203         for (;;)
 204         {
 205                 PlanState  *subnode;
 206                 TupleTableSlot *result;
 207
 208                 CHECK_FOR_INTERRUPTS();
 209
 210                 /*
 211                  * figure out which subplan we are currently processing
 212                  */
 213                 subnode = node->appendplans[node->as_whichplan];
 214
 215                 /*
 216                  * get a tuple from the subplan
 217                  */
 218                 result = ExecProcNode(subnode);
 219
 220                 if (!TupIsNull(result))
 221                 {
 222                         /*
 223                          * If the subplan gave us something then return it as-is. We do
 224                          * NOT make use of the result slot that was set up in
 225                          * ExecInitAppend; there's no need for it.
 226                          */
 227                         return result;
 228                 }
 229
 230                 /*
 231                  * Go on to the "next" subplan in the appropriate direction. If no
 232                  * more subplans, return the empty slot set up for us by
 233                  * ExecInitAppend.
 234                  */
 235                 if (ScanDirectionIsForward(node->ps.state->es_direction))
 236                         node->as_whichplan++;
 237                 else
 238                         node->as_whichplan--;
 239                 if (!exec_append_initialize_next(node))
 240                         return ExecClearTuple(node->ps.ps_ResultTupleSlot);
 241
 242                 /* Else loop back and try to get a tuple from the new subplan */
 243         }
 244 }
 245
 246 /* ----------------------------------------------------------------
 247  *              ExecEndAppend
 248  *
 249  *              Shuts down the subscans of the append node.
 250  *
 251  *              Returns nothing of interest.
 252  * ----------------------------------------------------------------
 253  */
 254 void
 255 ExecEndAppend(AppendState *node)
 256 {
 257         PlanState **appendplans;
 258         int                     nplans;
 259         int                     i;
 260
 261         /*
 262          * get information from the node
 263          */
 264         appendplans = node->appendplans;
 265         nplans = node->as_nplans;
 266
 267         /*
 268          * shut down each of the subscans
 269          */
 270         for (i = 0; i < nplans; i++)
 271                 ExecEndNode(appendplans[i]);
 272 }
 273
 274 void
 275 ExecReScanAppend(AppendState *node)
 276 {
 277         int                     i;
 278
 279         for (i = 0; i < node->as_nplans; i++)
 280         {
 281                 PlanState  *subnode = node->appendplans[i];
 282
 283                 /*
 284                  * ExecReScan doesn't know about my subplans, so I have to do
 285                  * changed-parameter signaling myself.
 286                  */
 287                 if (node->ps.chgParam != NULL)
 288                         UpdateChangedParamSet(subnode, node->ps.chgParam);
 289
 290                 /*
 291                  * If chgParam of subnode is not null then plan will be re-scanned by
 292                  * first ExecProcNode.
 293                  */
 294                 if (subnode->chgParam == NULL)
 295                         ExecReScan(subnode);
 296         }
 297         node->as_whichplan = 0;
 298         exec_append_initialize_next(node);
 299 }