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nodeCtescan.c
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1 /*-------------------------------------------------------------------------
2  *
3  * nodeCtescan.c
4  * routines to handle CteScan nodes.
5  *
6  * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
7  * Portions Copyright (c) 1994, Regents of the University of California
8  *
9  *
10  * IDENTIFICATION
11  * src/backend/executor/nodeCtescan.c
12  *
13  *-------------------------------------------------------------------------
14  */
15 
16 #include "postgres.h"
17 
18 #include "executor/execdebug.h"
19 #include "executor/nodeCtescan.h"
20 #include "miscadmin.h"
21 
23 
24 /* ----------------------------------------------------------------
25  * CteScanNext
26  *
27  * This is a workhorse for ExecCteScan
28  * ----------------------------------------------------------------
29  */
30 static TupleTableSlot *
32 {
33  EState *estate;
34  ScanDirection dir;
35  bool forward;
36  Tuplestorestate *tuplestorestate;
37  bool eof_tuplestore;
38  TupleTableSlot *slot;
39 
40  /*
41  * get state info from node
42  */
43  estate = node->ss.ps.state;
44  dir = estate->es_direction;
45  forward = ScanDirectionIsForward(dir);
46  tuplestorestate = node->leader->cte_table;
47  tuplestore_select_read_pointer(tuplestorestate, node->readptr);
48  slot = node->ss.ss_ScanTupleSlot;
49 
50  /*
51  * If we are not at the end of the tuplestore, or are going backwards, try
52  * to fetch a tuple from tuplestore.
53  */
54  eof_tuplestore = tuplestore_ateof(tuplestorestate);
55 
56  if (!forward && eof_tuplestore)
57  {
58  if (!node->leader->eof_cte)
59  {
60  /*
61  * When reversing direction at tuplestore EOF, the first
62  * gettupleslot call will fetch the last-added tuple; but we want
63  * to return the one before that, if possible. So do an extra
64  * fetch.
65  */
66  if (!tuplestore_advance(tuplestorestate, forward))
67  return NULL; /* the tuplestore must be empty */
68  }
69  eof_tuplestore = false;
70  }
71 
72  /*
73  * If we can fetch another tuple from the tuplestore, return it.
74  *
75  * Note: we have to use copy=true in the tuplestore_gettupleslot call,
76  * because we are sharing the tuplestore with other nodes that might write
77  * into the tuplestore before we get called again.
78  */
79  if (!eof_tuplestore)
80  {
81  if (tuplestore_gettupleslot(tuplestorestate, forward, true, slot))
82  return slot;
83  if (forward)
84  eof_tuplestore = true;
85  }
86 
87  /*
88  * If necessary, try to fetch another row from the CTE query.
89  *
90  * Note: the eof_cte state variable exists to short-circuit further calls
91  * of the CTE plan. It's not optional, unfortunately, because some plan
92  * node types are not robust about being called again when they've already
93  * returned NULL.
94  */
95  if (eof_tuplestore && !node->leader->eof_cte)
96  {
97  TupleTableSlot *cteslot;
98 
99  /*
100  * We can only get here with forward==true, so no need to worry about
101  * which direction the subplan will go.
102  */
103  cteslot = ExecProcNode(node->cteplanstate);
104  if (TupIsNull(cteslot))
105  {
106  node->leader->eof_cte = true;
107  return NULL;
108  }
109 
110  /*
111  * There are corner cases where the subplan could change which
112  * tuplestore read pointer is active, so be sure to reselect ours
113  * before storing the tuple we got.
114  */
115  tuplestore_select_read_pointer(tuplestorestate, node->readptr);
116 
117  /*
118  * Append a copy of the returned tuple to tuplestore. NOTE: because
119  * our read pointer is certainly in EOF state, its read position will
120  * move forward over the added tuple. This is what we want. Also,
121  * any other readers will *not* move past the new tuple, which is what
122  * they want.
123  */
124  tuplestore_puttupleslot(tuplestorestate, cteslot);
125 
126  /*
127  * We MUST copy the CTE query's output tuple into our own slot. This
128  * is because other CteScan nodes might advance the CTE query before
129  * we are called again, and our output tuple must stay stable over
130  * that.
131  */
132  return ExecCopySlot(slot, cteslot);
133  }
134 
135  /*
136  * Nothing left ...
137  */
138  return ExecClearTuple(slot);
139 }
140 
141 /*
142  * CteScanRecheck -- access method routine to recheck a tuple in EvalPlanQual
143  */
144 static bool
146 {
147  /* nothing to check */
148  return true;
149 }
150 
151 /* ----------------------------------------------------------------
152  * ExecCteScan(node)
153  *
154  * Scans the CTE sequentially and returns the next qualifying tuple.
155  * We call the ExecScan() routine and pass it the appropriate
156  * access method functions.
157  * ----------------------------------------------------------------
158  */
159 static TupleTableSlot *
161 {
162  CteScanState *node = castNode(CteScanState, pstate);
163 
164  return ExecScan(&node->ss,
167 }
168 
169 
170 /* ----------------------------------------------------------------
171  * ExecInitCteScan
172  * ----------------------------------------------------------------
173  */
174 CteScanState *
175 ExecInitCteScan(CteScan *node, EState *estate, int eflags)
176 {
177  CteScanState *scanstate;
178  ParamExecData *prmdata;
179 
180  /* check for unsupported flags */
181  Assert(!(eflags & EXEC_FLAG_MARK));
182 
183  /*
184  * For the moment we have to force the tuplestore to allow REWIND, because
185  * we might be asked to rescan the CTE even though upper levels didn't
186  * tell us to be prepared to do it efficiently. Annoying, since this
187  * prevents truncation of the tuplestore. XXX FIXME
188  *
189  * Note: if we are in an EPQ recheck plan tree, it's likely that no access
190  * to the tuplestore is needed at all, making this even more annoying.
191  * It's not worth improving that as long as all the read pointers would
192  * have REWIND anyway, but if we ever improve this logic then that aspect
193  * should be considered too.
194  */
195  eflags |= EXEC_FLAG_REWIND;
196 
197  /*
198  * CteScan should not have any children.
199  */
200  Assert(outerPlan(node) == NULL);
201  Assert(innerPlan(node) == NULL);
202 
203  /*
204  * create new CteScanState for node
205  */
206  scanstate = makeNode(CteScanState);
207  scanstate->ss.ps.plan = (Plan *) node;
208  scanstate->ss.ps.state = estate;
209  scanstate->ss.ps.ExecProcNode = ExecCteScan;
210  scanstate->eflags = eflags;
211  scanstate->cte_table = NULL;
212  scanstate->eof_cte = false;
213 
214  /*
215  * Find the already-initialized plan for the CTE query.
216  */
217  scanstate->cteplanstate = (PlanState *) list_nth(estate->es_subplanstates,
218  node->ctePlanId - 1);
219 
220  /*
221  * The Param slot associated with the CTE query is used to hold a pointer
222  * to the CteState of the first CteScan node that initializes for this
223  * CTE. This node will be the one that holds the shared state for all the
224  * CTEs, particularly the shared tuplestore.
225  */
226  prmdata = &(estate->es_param_exec_vals[node->cteParam]);
227  Assert(prmdata->execPlan == NULL);
228  Assert(!prmdata->isnull);
229  scanstate->leader = castNode(CteScanState, DatumGetPointer(prmdata->value));
230  if (scanstate->leader == NULL)
231  {
232  /* I am the leader */
233  prmdata->value = PointerGetDatum(scanstate);
234  scanstate->leader = scanstate;
235  scanstate->cte_table = tuplestore_begin_heap(true, false, work_mem);
236  tuplestore_set_eflags(scanstate->cte_table, scanstate->eflags);
237  scanstate->readptr = 0;
238  }
239  else
240  {
241  /* Not the leader */
242  /* Create my own read pointer, and ensure it is at start */
243  scanstate->readptr =
245  scanstate->eflags);
247  scanstate->readptr);
248  tuplestore_rescan(scanstate->leader->cte_table);
249  }
250 
251  /*
252  * Miscellaneous initialization
253  *
254  * create expression context for node
255  */
256  ExecAssignExprContext(estate, &scanstate->ss.ps);
257 
258  /*
259  * The scan tuple type (ie, the rowtype we expect to find in the work
260  * table) is the same as the result rowtype of the CTE query.
261  */
262  ExecInitScanTupleSlot(estate, &scanstate->ss,
263  ExecGetResultType(scanstate->cteplanstate));
264 
265  /*
266  * Initialize result slot, type and projection.
267  */
268  ExecInitResultTupleSlotTL(estate, &scanstate->ss.ps);
269  ExecAssignScanProjectionInfo(&scanstate->ss);
270 
271  /*
272  * initialize child expressions
273  */
274  scanstate->ss.ps.qual =
275  ExecInitQual(node->scan.plan.qual, (PlanState *) scanstate);
276 
277  return scanstate;
278 }
279 
280 /* ----------------------------------------------------------------
281  * ExecEndCteScan
282  *
283  * frees any storage allocated through C routines.
284  * ----------------------------------------------------------------
285  */
286 void
288 {
289  /*
290  * Free exprcontext
291  */
292  ExecFreeExprContext(&node->ss.ps);
293 
294  /*
295  * clean out the tuple table
296  */
299 
300  /*
301  * If I am the leader, free the tuplestore.
302  */
303  if (node->leader == node)
304  {
305  tuplestore_end(node->cte_table);
306  node->cte_table = NULL;
307  }
308 }
309 
310 /* ----------------------------------------------------------------
311  * ExecReScanCteScan
312  *
313  * Rescans the relation.
314  * ----------------------------------------------------------------
315  */
316 void
318 {
319  Tuplestorestate *tuplestorestate = node->leader->cte_table;
320 
322 
323  ExecScanReScan(&node->ss);
324 
325  /*
326  * Clear the tuplestore if a new scan of the underlying CTE is required.
327  * This implicitly resets all the tuplestore's read pointers. Note that
328  * multiple CTE nodes might redundantly clear the tuplestore; that's OK,
329  * and not unduly expensive. We'll stop taking this path as soon as
330  * somebody has attempted to read something from the underlying CTE
331  * (thereby causing its chgParam to be cleared).
332  */
333  if (node->leader->cteplanstate->chgParam != NULL)
334  {
335  tuplestore_clear(tuplestorestate);
336  node->leader->eof_cte = false;
337  }
338  else
339  {
340  /*
341  * Else, just rewind my own pointer. Either the underlying CTE
342  * doesn't need a rescan (and we can re-read what's in the tuplestore
343  * now), or somebody else already took care of it.
344  */
345  tuplestore_select_read_pointer(tuplestorestate, node->readptr);
346  tuplestore_rescan(tuplestorestate);
347  }
348 }
void tuplestore_rescan(Tuplestorestate *state)
Definition: tuplestore.c:1233
static TupleTableSlot * ExecCteScan(PlanState *pstate)
Definition: nodeCtescan.c:160
static bool CteScanRecheck(CteScanState *node, TupleTableSlot *slot)
Definition: nodeCtescan.c:145
void tuplestore_puttupleslot(Tuplestorestate *state, TupleTableSlot *slot)
Definition: tuplestore.c:708
List * qual
Definition: plannodes.h:147
void * execPlan
Definition: params.h:147
Plan plan
Definition: plannodes.h:342
bool tuplestore_advance(Tuplestorestate *state, bool forward)
Definition: tuplestore.c:1110
#define ScanDirectionIsForward(direction)
Definition: sdir.h:55
#define castNode(_type_, nodeptr)
Definition: nodes.h:586
void tuplestore_set_eflags(Tuplestorestate *state, int eflags)
Definition: tuplestore.c:359
#define PointerGetDatum(X)
Definition: postgres.h:541
TupleTableSlot * ExecScan(ScanState *node, ExecScanAccessMtd accessMtd, ExecScanRecheckMtd recheckMtd)
Definition: execScan.c:121
TupleTableSlot * ExecClearTuple(TupleTableSlot *slot)
Definition: execTuples.c:475
CteScanState * ExecInitCteScan(CteScan *node, EState *estate, int eflags)
Definition: nodeCtescan.c:175
struct CteScanState * leader
Definition: execnodes.h:1595
ScanState ss
Definition: execnodes.h:1590
TupleTableSlot * ss_ScanTupleSlot
Definition: execnodes.h:1195
EState * state
Definition: execnodes.h:914
void ExecFreeExprContext(PlanState *planstate)
Definition: execUtils.c:566
ScanDirection es_direction
Definition: execnodes.h:477
ExprState * ExecInitQual(List *qual, PlanState *parent)
Definition: execExpr.c:205
PlanState ps
Definition: execnodes.h:1192
TupleTableSlot * ps_ResultTupleSlot
Definition: execnodes.h:946
ParamExecData * es_param_exec_vals
Definition: execnodes.h:518
int cteParam
Definition: plannodes.h:554
void ExecAssignScanProjectionInfo(ScanState *node)
Definition: execScan.c:235
bool isnull
Definition: params.h:149
Scan scan
Definition: plannodes.h:552
void tuplestore_clear(Tuplestorestate *state)
Definition: tuplestore.c:418
#define innerPlan(node)
Definition: plannodes.h:175
void * list_nth(const List *list, int n)
Definition: list.c:410
int ctePlanId
Definition: plannodes.h:553
ScanDirection
Definition: sdir.h:22
#define TupIsNull(slot)
Definition: tuptable.h:146
#define EXEC_FLAG_REWIND
Definition: executor.h:59
Bitmapset * chgParam
Definition: execnodes.h:941
#define outerPlan(node)
Definition: plannodes.h:176
bool(* ExecScanRecheckMtd)(ScanState *node, TupleTableSlot *slot)
Definition: executor.h:422
Tuplestorestate * tuplestore_begin_heap(bool randomAccess, bool interXact, int maxKBytes)
Definition: tuplestore.c:318
ExecProcNodeMtd ExecProcNode
Definition: execnodes.h:918
void ExecEndCteScan(CteScanState *node)
Definition: nodeCtescan.c:287
static TupleTableSlot * ExecProcNode(PlanState *node)
Definition: executor.h:233
int work_mem
Definition: globals.c:120
void ExecInitResultTupleSlotTL(EState *estate, PlanState *planstate)
Definition: execTuples.c:890
Plan * plan
Definition: execnodes.h:912
TupleTableSlot * ExecCopySlot(TupleTableSlot *dstslot, TupleTableSlot *srcslot)
Definition: execTuples.c:851
#define makeNode(_type_)
Definition: nodes.h:565
bool tuplestore_gettupleslot(Tuplestorestate *state, bool forward, bool copy, TupleTableSlot *slot)
Definition: tuplestore.c:1078
#define Assert(condition)
Definition: c.h:699
#define EXEC_FLAG_MARK
Definition: executor.h:61
void ExecAssignExprContext(EState *estate, PlanState *planstate)
Definition: execUtils.c:428
void tuplestore_end(Tuplestorestate *state)
Definition: tuplestore.c:453
List * es_subplanstates
Definition: execnodes.h:538
TupleDesc ExecGetResultType(PlanState *planstate)
Definition: execUtils.c:438
ExprState * qual
Definition: execnodes.h:930
#define DatumGetPointer(X)
Definition: postgres.h:534
int tuplestore_alloc_read_pointer(Tuplestorestate *state, int eflags)
Definition: tuplestore.c:383
PlanState * cteplanstate
Definition: execnodes.h:1593
static TupleTableSlot * CteScanNext(CteScanState *node)
Definition: nodeCtescan.c:31
void ExecScanReScan(ScanState *node)
Definition: execScan.c:262
void ExecReScanCteScan(CteScanState *node)
Definition: nodeCtescan.c:317
void tuplestore_select_read_pointer(Tuplestorestate *state, int ptr)
Definition: tuplestore.c:473
Datum value
Definition: params.h:148
void ExecInitScanTupleSlot(EState *estate, ScanState *scanstate, TupleDesc tupledesc)
Definition: execTuples.c:915
bool tuplestore_ateof(Tuplestorestate *state)
Definition: tuplestore.c:557
TupleTableSlot *(* ExecScanAccessMtd)(ScanState *node)
Definition: executor.h:421
Tuplestorestate * cte_table
Definition: execnodes.h:1597