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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) 1996-2023, 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  if (!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)
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)
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);
199 
200  /*
201  * Miscellaneous initialization
202  *
203  * create expression context for node
204  */
205  ExecAssignExprContext(estate, &resstate->ps);
206 
207  /*
208  * initialize child nodes
209  */
210  outerPlanState(resstate) = ExecInitNode(outerPlan(node), estate, eflags);
211 
212  /*
213  * we don't use inner plan
214  */
215  Assert(innerPlan(node) == NULL);
216 
217  /*
218  * Initialize result slot, type and projection.
219  */
221  ExecAssignProjectionInfo(&resstate->ps, NULL);
222 
223  /*
224  * initialize child expressions
225  */
226  resstate->ps.qual =
227  ExecInitQual(node->plan.qual, (PlanState *) resstate);
228  resstate->resconstantqual =
229  ExecInitQual((List *) node->resconstantqual, (PlanState *) resstate);
230 
231  return resstate;
232 }
233 
234 /* ----------------------------------------------------------------
235  * ExecEndResult
236  *
237  * frees up storage allocated through C routines
238  * ----------------------------------------------------------------
239  */
240 void
242 {
243  /*
244  * Free the exprcontext
245  */
246  ExecFreeExprContext(&node->ps);
247 
248  /*
249  * clean out the tuple table
250  */
252 
253  /*
254  * shut down subplans
255  */
257 }
258 
259 void
261 {
263 
264  node->rs_done = false;
265  node->rs_checkqual = (node->resconstantqual != NULL);
266 
267  /*
268  * If chgParam of subnode is not null then plan will be re-scanned by
269  * first ExecProcNode.
270  */
271  if (outerPlan && outerPlan->chgParam == NULL)
273 }
#define DEBUG2
Definition: elog.h:29
#define ERROR
Definition: elog.h:39
void ExecMarkPos(PlanState *node)
Definition: execAmi.c:328
void ExecReScan(PlanState *node)
Definition: execAmi.c:78
void ExecRestrPos(PlanState *node)
Definition: execAmi.c:377
ExprState * ExecInitQual(List *qual, PlanState *parent)
Definition: execExpr.c:213
void ExecEndNode(PlanState *node)
Definition: execProcnode.c:557
PlanState * ExecInitNode(Plan *node, EState *estate, int eflags)
Definition: execProcnode.c:142
const TupleTableSlotOps TTSOpsVirtual
Definition: execTuples.c:83
void ExecInitResultTupleSlotTL(PlanState *planstate, const TupleTableSlotOps *tts_ops)
Definition: execTuples.c:1800
void ExecAssignExprContext(EState *estate, PlanState *planstate)
Definition: execUtils.c:488
void ExecAssignProjectionInfo(PlanState *planstate, TupleDesc inputDesc)
Definition: execUtils.c:543
void ExecFreeExprContext(PlanState *planstate)
Definition: execUtils.c:658
#define outerPlanState(node)
Definition: execnodes.h:1133
#define EXEC_FLAG_BACKWARD
Definition: executor.h:68
static TupleTableSlot * ExecProject(ProjectionInfo *projInfo)
Definition: executor.h:375
#define ResetExprContext(econtext)
Definition: executor.h:543
static bool ExecQual(ExprState *state, ExprContext *econtext)
Definition: executor.h:412
#define EXEC_FLAG_MARK
Definition: executor.h:69
static TupleTableSlot * ExecProcNode(PlanState *node)
Definition: executor.h:268
Assert(fmt[strlen(fmt) - 1] !='\n')
#define CHECK_FOR_INTERRUPTS()
Definition: miscadmin.h:121
void ExecReScanResult(ResultState *node)
Definition: nodeResult.c:260
ResultState * ExecInitResult(Result *node, EState *estate, int eflags)
Definition: nodeResult.c:181
static TupleTableSlot * ExecResult(PlanState *pstate)
Definition: nodeResult.c:68
void ExecEndResult(ResultState *node)
Definition: nodeResult.c:241
void ExecResultRestrPos(ResultState *node)
Definition: nodeResult.c:162
void ExecResultMarkPos(ResultState *node)
Definition: nodeResult.c:147
#define makeNode(_type_)
Definition: nodes.h:176
#define castNode(_type_, nodeptr)
Definition: nodes.h:197
#define innerPlan(node)
Definition: plannodes.h:182
#define outerPlan(node)
Definition: plannodes.h:183
TupleTableSlot * ecxt_outertuple
Definition: execnodes.h:253
Definition: pg_list.h:54
ExprState * qual
Definition: execnodes.h:1058
Plan * plan
Definition: execnodes.h:1037
EState * state
Definition: execnodes.h:1039
ExprContext * ps_ExprContext
Definition: execnodes.h:1076
TupleTableSlot * ps_ResultTupleSlot
Definition: execnodes.h:1075
ProjectionInfo * ps_ProjInfo
Definition: execnodes.h:1077
ExecProcNodeMtd ExecProcNode
Definition: execnodes.h:1043
List * qual
Definition: plannodes.h:154
ExprState * resconstantqual
Definition: execnodes.h:1241
bool rs_done
Definition: execnodes.h:1242
PlanState ps
Definition: execnodes.h:1240
bool rs_checkqual
Definition: execnodes.h:1243
Node * resconstantqual
Definition: plannodes.h:200
Plan plan
Definition: plannodes.h:199
static TupleTableSlot * ExecClearTuple(TupleTableSlot *slot)
Definition: tuptable.h:433
#define TupIsNull(slot)
Definition: tuptable.h:300