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nodeResult.c
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1 /*-------------------------------------------------------------------------
2  *
3  * nodeResult.c
4  * support for constant nodes needing special code.
5  *
6  * DESCRIPTION
7  *
8  * Result nodes are used in queries where no relations are scanned.
9  * Examples of such queries are:
10  *
11  * select 1 * 2
12  *
13  * insert into emp values ('mike', 15000)
14  *
15  * (Remember that in an INSERT or UPDATE, we need a plan tree that
16  * generates the new rows.)
17  *
18  * Result nodes are also used to optimise queries with constant
19  * qualifications (ie, quals that do not depend on the scanned data),
20  * such as:
21  *
22  * select * from emp where 2 > 1
23  *
24  * In this case, the plan generated is
25  *
26  * Result (with 2 > 1 qual)
27  * /
28  * SeqScan (emp.*)
29  *
30  * At runtime, the Result node evaluates the constant qual once,
31  * which is shown by EXPLAIN as a One-Time Filter. If it's
32  * false, we can return an empty result set without running the
33  * controlled plan at all. If it's true, we run the controlled
34  * plan normally and pass back the results.
35  *
36  *
37  * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
38  * Portions Copyright (c) 1994, Regents of the University of California
39  *
40  * IDENTIFICATION
41  * src/backend/executor/nodeResult.c
42  *
43  *-------------------------------------------------------------------------
44  */
45 
46 #include "postgres.h"
47 
48 #include "executor/executor.h"
49 #include "executor/nodeResult.h"
50 #include "miscadmin.h"
51 #include "utils/memutils.h"
52 
53 
54 /* ----------------------------------------------------------------
55  * ExecResult(node)
56  *
57  * returns the tuples from the outer plan which satisfy the
58  * qualification clause. Since result nodes with right
59  * subtrees are never planned, we ignore the right subtree
60  * entirely (for now).. -cim 10/7/89
61  *
62  * The qualification containing only constant clauses are
63  * checked first before any processing is done. It always returns
64  * 'nil' if the constant qualification is not satisfied.
65  * ----------------------------------------------------------------
66  */
67 static TupleTableSlot *
69 {
70  ResultState *node = castNode(ResultState, pstate);
71  TupleTableSlot *outerTupleSlot;
73  ExprContext *econtext;
74 
76 
77  econtext = node->ps.ps_ExprContext;
78 
79  /*
80  * check constant qualifications like (2 > 1), if not already done
81  */
82  if (node->rs_checkqual)
83  {
84  bool qualResult = ExecQual(node->resconstantqual, econtext);
85 
86  node->rs_checkqual = false;
87  if (!qualResult)
88  {
89  node->rs_done = true;
90  return NULL;
91  }
92  }
93 
94  /*
95  * Reset per-tuple memory context to free any expression evaluation
96  * storage allocated in the previous tuple cycle.
97  */
98  ResetExprContext(econtext);
99 
100  /*
101  * if rs_done is true then it means that we were asked to return a
102  * constant tuple and we already did the last time ExecResult() was
103  * called, OR that we failed the constant qual check. Either way, now we
104  * are through.
105  */
106  while (!node->rs_done)
107  {
108  outerPlan = outerPlanState(node);
109 
110  if (outerPlan != NULL)
111  {
112  /*
113  * retrieve tuples from the outer plan until there are no more.
114  */
115  outerTupleSlot = ExecProcNode(outerPlan);
116 
117  if (TupIsNull(outerTupleSlot))
118  return NULL;
119 
120  /*
121  * prepare to compute projection expressions, which will expect to
122  * access the input tuples as varno OUTER.
123  */
124  econtext->ecxt_outertuple = outerTupleSlot;
125  }
126  else
127  {
128  /*
129  * if we don't have an outer plan, then we are just generating the
130  * results from a constant target list. Do it only once.
131  */
132  node->rs_done = true;
133  }
134 
135  /* form the result tuple using ExecProject(), and return it */
136  return ExecProject(node->ps.ps_ProjInfo);
137  }
138 
139  return NULL;
140 }
141 
142 /* ----------------------------------------------------------------
143  * ExecResultMarkPos
144  * ----------------------------------------------------------------
145  */
146 void
148 {
150 
151  if (outerPlan != NULL)
152  ExecMarkPos(outerPlan);
153  else
154  elog(DEBUG2, "Result nodes do not support mark/restore");
155 }
156 
157 /* ----------------------------------------------------------------
158  * ExecResultRestrPos
159  * ----------------------------------------------------------------
160  */
161 void
163 {
165 
166  if (outerPlan != NULL)
167  ExecRestrPos(outerPlan);
168  else
169  elog(ERROR, "Result nodes do not support mark/restore");
170 }
171 
172 /* ----------------------------------------------------------------
173  * ExecInitResult
174  *
175  * Creates the run-time state information for the result node
176  * produced by the planner and initializes outer relations
177  * (child nodes).
178  * ----------------------------------------------------------------
179  */
180 ResultState *
181 ExecInitResult(Result *node, EState *estate, int eflags)
182 {
183  ResultState *resstate;
184 
185  /* check for unsupported flags */
186  Assert(!(eflags & (EXEC_FLAG_MARK | EXEC_FLAG_BACKWARD)) ||
187  outerPlan(node) != NULL);
188 
189  /*
190  * create state structure
191  */
192  resstate = makeNode(ResultState);
193  resstate->ps.plan = (Plan *) node;
194  resstate->ps.state = estate;
195  resstate->ps.ExecProcNode = ExecResult;
196 
197  resstate->rs_done = false;
198  resstate->rs_checkqual = (node->resconstantqual == NULL) ? false : true;
199 
200  /*
201  * Miscellaneous initialization
202  *
203  * create expression context for node
204  */
205  ExecAssignExprContext(estate, &resstate->ps);
206 
207  /*
208  * tuple table initialization
209  */
210  ExecInitResultTupleSlot(estate, &resstate->ps);
211 
212  /*
213  * initialize child expressions
214  */
215  resstate->ps.qual =
216  ExecInitQual(node->plan.qual, (PlanState *) resstate);
217  resstate->resconstantqual =
218  ExecInitQual((List *) node->resconstantqual, (PlanState *) resstate);
219 
220  /*
221  * initialize child nodes
222  */
223  outerPlanState(resstate) = ExecInitNode(outerPlan(node), estate, eflags);
224 
225  /*
226  * we don't use inner plan
227  */
228  Assert(innerPlan(node) == NULL);
229 
230  /*
231  * initialize tuple type and projection info
232  */
233  ExecAssignResultTypeFromTL(&resstate->ps);
234  ExecAssignProjectionInfo(&resstate->ps, NULL);
235 
236  return resstate;
237 }
238 
239 /* ----------------------------------------------------------------
240  * ExecEndResult
241  *
242  * frees up storage allocated through C routines
243  * ----------------------------------------------------------------
244  */
245 void
247 {
248  /*
249  * Free the exprcontext
250  */
251  ExecFreeExprContext(&node->ps);
252 
253  /*
254  * clean out the tuple table
255  */
257 
258  /*
259  * shut down subplans
260  */
262 }
263 
264 void
266 {
267  node->rs_done = false;
268  node->rs_checkqual = (node->resconstantqual == NULL) ? false : true;
269 
270  /*
271  * If chgParam of subnode is not null then plan will be re-scanned by
272  * first ExecProcNode.
273  */
274  if (node->ps.lefttree &&
275  node->ps.lefttree->chgParam == NULL)
276  ExecReScan(node->ps.lefttree);
277 }
Plan plan
Definition: plannodes.h:190
List * qual
Definition: plannodes.h:145
bool rs_done
Definition: execnodes.h:931
ProjectionInfo * ps_ProjInfo
Definition: execnodes.h:882
#define castNode(_type_, nodeptr)
Definition: nodes.h:579
void ExecEndNode(PlanState *node)
Definition: execProcnode.c:523
ExprContext * ps_ExprContext
Definition: execnodes.h:881
void ExecReScan(PlanState *node)
Definition: execAmi.c:76
TupleTableSlot * ExecClearTuple(TupleTableSlot *slot)
Definition: execTuples.c:439
EState * state
Definition: execnodes.h:849
static bool ExecQual(ExprState *state, ExprContext *econtext)
Definition: executor.h:366
void ExecReScanResult(ResultState *node)
Definition: nodeResult.c:265
void ExecResultRestrPos(ResultState *node)
Definition: nodeResult.c:162
void ExecFreeExprContext(PlanState *planstate)
Definition: execUtils.c:521
ExprState * ExecInitQual(List *qual, PlanState *parent)
Definition: execExpr.c:160
void ExecAssignResultTypeFromTL(PlanState *planstate)
Definition: execUtils.c:445
struct PlanState * lefttree
Definition: execnodes.h:866
Node * resconstantqual
Definition: plannodes.h:191
void ExecRestrPos(PlanState *node)
Definition: execAmi.c:363
TupleTableSlot * ps_ResultTupleSlot
Definition: execnodes.h:880
void ExecEndResult(ResultState *node)
Definition: nodeResult.c:246
#define ERROR
Definition: elog.h:43
void ExecInitResultTupleSlot(EState *estate, PlanState *planstate)
Definition: execTuples.c:832
ExprState * resconstantqual
Definition: execnodes.h:930
#define EXEC_FLAG_BACKWARD
Definition: executor.h:60
#define outerPlanState(node)
Definition: execnodes.h:893
#define innerPlan(node)
Definition: plannodes.h:173
#define DEBUG2
Definition: elog.h:24
void ExecAssignProjectionInfo(PlanState *planstate, TupleDesc inputDesc)
Definition: execUtils.c:492
#define TupIsNull(slot)
Definition: tuptable.h:138
Bitmapset * chgParam
Definition: execnodes.h:875
#define outerPlan(node)
Definition: plannodes.h:174
bool rs_checkqual
Definition: execnodes.h:932
static TupleTableSlot * ExecResult(PlanState *pstate)
Definition: nodeResult.c:68
ExecProcNodeMtd ExecProcNode
Definition: execnodes.h:853
static TupleTableSlot * ExecProcNode(PlanState *node)
Definition: executor.h:246
Plan * plan
Definition: execnodes.h:847
void ExecMarkPos(PlanState *node)
Definition: execAmi.c:314
#define makeNode(_type_)
Definition: nodes.h:558
TupleTableSlot * ecxt_outertuple
Definition: execnodes.h:199
#define Assert(condition)
Definition: c.h:681
#define EXEC_FLAG_MARK
Definition: executor.h:61
ResultState * ExecInitResult(Result *node, EState *estate, int eflags)
Definition: nodeResult.c:181
void ExecAssignExprContext(EState *estate, PlanState *planstate)
Definition: execUtils.c:423
void ExecResultMarkPos(ResultState *node)
Definition: nodeResult.c:147
ExprState * qual
Definition: execnodes.h:865
#define CHECK_FOR_INTERRUPTS()
Definition: miscadmin.h:98
#define elog
Definition: elog.h:219
PlanState * ExecInitNode(Plan *node, EState *estate, int eflags)
Definition: execProcnode.c:139
Definition: pg_list.h:45
static TupleTableSlot * ExecProject(ProjectionInfo *projInfo)
Definition: executor.h:329
#define ResetExprContext(econtext)
Definition: executor.h:471
PlanState ps
Definition: execnodes.h:929