Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * portalcmds.c
4 : * Utility commands affecting portals (that is, SQL cursor commands)
5 : *
6 : * Note: see also tcop/pquery.c, which implements portal operations for
7 : * the FE/BE protocol. This module uses pquery.c for some operations.
8 : * And both modules depend on utils/mmgr/portalmem.c, which controls
9 : * storage management for portals (but doesn't run any queries in them).
10 : *
11 : *
12 : * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
13 : * Portions Copyright (c) 1994, Regents of the University of California
14 : *
15 : *
16 : * IDENTIFICATION
17 : * src/backend/commands/portalcmds.c
18 : *
19 : *-------------------------------------------------------------------------
20 : */
21 :
22 : #include "postgres.h"
23 :
24 : #include <limits.h>
25 :
26 : #include "access/xact.h"
27 : #include "commands/portalcmds.h"
28 : #include "executor/executor.h"
29 : #include "executor/tstoreReceiver.h"
30 : #include "miscadmin.h"
31 : #include "nodes/queryjumble.h"
32 : #include "parser/analyze.h"
33 : #include "rewrite/rewriteHandler.h"
34 : #include "tcop/pquery.h"
35 : #include "tcop/tcopprot.h"
36 : #include "utils/memutils.h"
37 : #include "utils/snapmgr.h"
38 :
39 :
40 : /*
41 : * PerformCursorOpen
42 : * Execute SQL DECLARE CURSOR command.
43 : */
44 : void
45 2700 : PerformCursorOpen(ParseState *pstate, DeclareCursorStmt *cstmt, ParamListInfo params,
46 : bool isTopLevel)
47 : {
48 2700 : Query *query = castNode(Query, cstmt->query);
49 2700 : JumbleState *jstate = NULL;
50 : List *rewritten;
51 : PlannedStmt *plan;
52 : Portal portal;
53 : MemoryContext oldContext;
54 : char *queryString;
55 :
56 : /*
57 : * Disallow empty-string cursor name (conflicts with protocol-level
58 : * unnamed portal).
59 : */
60 2700 : if (!cstmt->portalname || cstmt->portalname[0] == '\0')
61 0 : ereport(ERROR,
62 : (errcode(ERRCODE_INVALID_CURSOR_NAME),
63 : errmsg("invalid cursor name: must not be empty")));
64 :
65 : /*
66 : * If this is a non-holdable cursor, we require that this statement has
67 : * been executed inside a transaction block (or else, it would have no
68 : * user-visible effect).
69 : */
70 2700 : if (!(cstmt->options & CURSOR_OPT_HOLD))
71 2626 : RequireTransactionBlock(isTopLevel, "DECLARE CURSOR");
72 74 : else if (InSecurityRestrictedOperation())
73 12 : ereport(ERROR,
74 : (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
75 : errmsg("cannot create a cursor WITH HOLD within security-restricted operation")));
76 :
77 : /* Query contained by DeclareCursor needs to be jumbled if requested */
78 2686 : if (IsQueryIdEnabled())
79 212 : jstate = JumbleQuery(query);
80 :
81 2686 : if (post_parse_analyze_hook)
82 212 : (*post_parse_analyze_hook) (pstate, query, jstate);
83 :
84 : /*
85 : * Parse analysis was done already, but we still have to run the rule
86 : * rewriter. We do not do AcquireRewriteLocks: we assume the query either
87 : * came straight from the parser, or suitable locks were acquired by
88 : * plancache.c.
89 : */
90 2686 : rewritten = QueryRewrite(query);
91 :
92 : /* SELECT should never rewrite to more or less than one query */
93 2686 : if (list_length(rewritten) != 1)
94 0 : elog(ERROR, "non-SELECT statement in DECLARE CURSOR");
95 :
96 2686 : query = linitial_node(Query, rewritten);
97 :
98 2686 : if (query->commandType != CMD_SELECT)
99 0 : elog(ERROR, "non-SELECT statement in DECLARE CURSOR");
100 :
101 : /* Plan the query, applying the specified options */
102 2686 : plan = pg_plan_query(query, pstate->p_sourcetext, cstmt->options, params);
103 :
104 : /*
105 : * Create a portal and copy the plan and query string into its memory.
106 : */
107 2686 : portal = CreatePortal(cstmt->portalname, false, false);
108 :
109 2686 : oldContext = MemoryContextSwitchTo(portal->portalContext);
110 :
111 2686 : plan = copyObject(plan);
112 :
113 2686 : queryString = pstrdup(pstate->p_sourcetext);
114 :
115 2686 : PortalDefineQuery(portal,
116 : NULL,
117 : queryString,
118 : CMDTAG_SELECT, /* cursor's query is always a SELECT */
119 2686 : list_make1(plan),
120 : NULL);
121 :
122 : /*----------
123 : * Also copy the outer portal's parameter list into the inner portal's
124 : * memory context. We want to pass down the parameter values in case we
125 : * had a command like
126 : * DECLARE c CURSOR FOR SELECT ... WHERE foo = $1
127 : * This will have been parsed using the outer parameter set and the
128 : * parameter value needs to be preserved for use when the cursor is
129 : * executed.
130 : *----------
131 : */
132 2686 : params = copyParamList(params);
133 :
134 2686 : MemoryContextSwitchTo(oldContext);
135 :
136 : /*
137 : * Set up options for portal.
138 : *
139 : * If the user didn't specify a SCROLL type, allow or disallow scrolling
140 : * based on whether it would require any additional runtime overhead to do
141 : * so. Also, we disallow scrolling for FOR UPDATE cursors.
142 : */
143 2686 : portal->cursorOptions = cstmt->options;
144 2686 : if (!(portal->cursorOptions & (CURSOR_OPT_SCROLL | CURSOR_OPT_NO_SCROLL)))
145 : {
146 4752 : if (plan->rowMarks == NIL &&
147 2300 : ExecSupportsBackwardScan(plan->planTree))
148 1544 : portal->cursorOptions |= CURSOR_OPT_SCROLL;
149 : else
150 908 : portal->cursorOptions |= CURSOR_OPT_NO_SCROLL;
151 : }
152 :
153 : /*
154 : * Start execution, inserting parameters if any.
155 : */
156 2686 : PortalStart(portal, params, 0, GetActiveSnapshot());
157 :
158 : Assert(portal->strategy == PORTAL_ONE_SELECT);
159 :
160 : /*
161 : * We're done; the query won't actually be run until PerformPortalFetch is
162 : * called.
163 : */
164 2686 : }
165 :
166 : /*
167 : * PerformPortalFetch
168 : * Execute SQL FETCH or MOVE command.
169 : *
170 : * stmt: parsetree node for command
171 : * dest: where to send results
172 : * qc: where to store a command completion status data.
173 : *
174 : * qc may be NULL if caller doesn't want status data.
175 : */
176 : void
177 5748 : PerformPortalFetch(FetchStmt *stmt,
178 : DestReceiver *dest,
179 : QueryCompletion *qc)
180 : {
181 : Portal portal;
182 : uint64 nprocessed;
183 :
184 : /*
185 : * Disallow empty-string cursor name (conflicts with protocol-level
186 : * unnamed portal).
187 : */
188 5748 : if (!stmt->portalname || stmt->portalname[0] == '\0')
189 0 : ereport(ERROR,
190 : (errcode(ERRCODE_INVALID_CURSOR_NAME),
191 : errmsg("invalid cursor name: must not be empty")));
192 :
193 : /* get the portal from the portal name */
194 5748 : portal = GetPortalByName(stmt->portalname);
195 5748 : if (!PortalIsValid(portal))
196 : {
197 34 : ereport(ERROR,
198 : (errcode(ERRCODE_UNDEFINED_CURSOR),
199 : errmsg("cursor \"%s\" does not exist", stmt->portalname)));
200 : return; /* keep compiler happy */
201 : }
202 :
203 : /* Adjust dest if needed. MOVE wants destination DestNone */
204 5714 : if (stmt->ismove)
205 68 : dest = None_Receiver;
206 :
207 : /* Do it */
208 5714 : nprocessed = PortalRunFetch(portal,
209 : stmt->direction,
210 : stmt->howMany,
211 : dest);
212 :
213 : /* Return command status if wanted */
214 5658 : if (qc)
215 5658 : SetQueryCompletion(qc, stmt->ismove ? CMDTAG_MOVE : CMDTAG_FETCH,
216 : nprocessed);
217 : }
218 :
219 : /*
220 : * PerformPortalClose
221 : * Close a cursor.
222 : */
223 : void
224 2194 : PerformPortalClose(const char *name)
225 : {
226 : Portal portal;
227 :
228 : /* NULL means CLOSE ALL */
229 2194 : if (name == NULL)
230 : {
231 12 : PortalHashTableDeleteAll();
232 12 : return;
233 : }
234 :
235 : /*
236 : * Disallow empty-string cursor name (conflicts with protocol-level
237 : * unnamed portal).
238 : */
239 2182 : if (name[0] == '\0')
240 0 : ereport(ERROR,
241 : (errcode(ERRCODE_INVALID_CURSOR_NAME),
242 : errmsg("invalid cursor name: must not be empty")));
243 :
244 : /*
245 : * get the portal from the portal name
246 : */
247 2182 : portal = GetPortalByName(name);
248 2182 : if (!PortalIsValid(portal))
249 : {
250 2 : ereport(ERROR,
251 : (errcode(ERRCODE_UNDEFINED_CURSOR),
252 : errmsg("cursor \"%s\" does not exist", name)));
253 : return; /* keep compiler happy */
254 : }
255 :
256 : /*
257 : * Note: PortalCleanup is called as a side-effect, if not already done.
258 : */
259 2180 : PortalDrop(portal, false);
260 : }
261 :
262 : /*
263 : * PortalCleanup
264 : *
265 : * Clean up a portal when it's dropped. This is the standard cleanup hook
266 : * for portals.
267 : *
268 : * Note: if portal->status is PORTAL_FAILED, we are probably being called
269 : * during error abort, and must be careful to avoid doing anything that
270 : * is likely to fail again.
271 : */
272 : void
273 683622 : PortalCleanup(Portal portal)
274 : {
275 : QueryDesc *queryDesc;
276 :
277 : /*
278 : * sanity checks
279 : */
280 : Assert(PortalIsValid(portal));
281 : Assert(portal->cleanup == PortalCleanup);
282 :
283 : /*
284 : * Shut down executor, if still running. We skip this during error abort,
285 : * since other mechanisms will take care of releasing executor resources,
286 : * and we can't be sure that ExecutorEnd itself wouldn't fail.
287 : */
288 683622 : queryDesc = portal->queryDesc;
289 683622 : if (queryDesc)
290 : {
291 : /*
292 : * Reset the queryDesc before anything else. This prevents us from
293 : * trying to shut down the executor twice, in case of an error below.
294 : * The transaction abort mechanisms will take care of resource cleanup
295 : * in such a case.
296 : */
297 260570 : portal->queryDesc = NULL;
298 :
299 260570 : if (portal->status != PORTAL_FAILED)
300 : {
301 : ResourceOwner saveResourceOwner;
302 :
303 : /* We must make the portal's resource owner current */
304 253310 : saveResourceOwner = CurrentResourceOwner;
305 253310 : if (portal->resowner)
306 253310 : CurrentResourceOwner = portal->resowner;
307 :
308 253310 : ExecutorFinish(queryDesc);
309 253310 : ExecutorEnd(queryDesc);
310 253310 : FreeQueryDesc(queryDesc);
311 :
312 253310 : CurrentResourceOwner = saveResourceOwner;
313 : }
314 : }
315 683622 : }
316 :
317 : /*
318 : * PersistHoldablePortal
319 : *
320 : * Prepare the specified Portal for access outside of the current
321 : * transaction. When this function returns, all future accesses to the
322 : * portal must be done via the Tuplestore (not by invoking the
323 : * executor).
324 : */
325 : void
326 82 : PersistHoldablePortal(Portal portal)
327 : {
328 82 : QueryDesc *queryDesc = portal->queryDesc;
329 : Portal saveActivePortal;
330 : ResourceOwner saveResourceOwner;
331 : MemoryContext savePortalContext;
332 : MemoryContext oldcxt;
333 :
334 : /*
335 : * If we're preserving a holdable portal, we had better be inside the
336 : * transaction that originally created it.
337 : */
338 : Assert(portal->createSubid != InvalidSubTransactionId);
339 : Assert(queryDesc != NULL);
340 :
341 : /*
342 : * Caller must have created the tuplestore already ... but not a snapshot.
343 : */
344 : Assert(portal->holdContext != NULL);
345 : Assert(portal->holdStore != NULL);
346 : Assert(portal->holdSnapshot == NULL);
347 :
348 : /*
349 : * Before closing down the executor, we must copy the tupdesc into
350 : * long-term memory, since it was created in executor memory.
351 : */
352 82 : oldcxt = MemoryContextSwitchTo(portal->holdContext);
353 :
354 82 : portal->tupDesc = CreateTupleDescCopy(portal->tupDesc);
355 :
356 82 : MemoryContextSwitchTo(oldcxt);
357 :
358 : /*
359 : * Check for improper portal use, and mark portal active.
360 : */
361 82 : MarkPortalActive(portal);
362 :
363 : /*
364 : * Set up global portal context pointers.
365 : */
366 82 : saveActivePortal = ActivePortal;
367 82 : saveResourceOwner = CurrentResourceOwner;
368 82 : savePortalContext = PortalContext;
369 82 : PG_TRY();
370 : {
371 82 : ScanDirection direction = ForwardScanDirection;
372 :
373 82 : ActivePortal = portal;
374 82 : if (portal->resowner)
375 82 : CurrentResourceOwner = portal->resowner;
376 82 : PortalContext = portal->portalContext;
377 :
378 82 : MemoryContextSwitchTo(PortalContext);
379 :
380 82 : PushActiveSnapshot(queryDesc->snapshot);
381 :
382 : /*
383 : * If the portal is marked scrollable, we need to store the entire
384 : * result set in the tuplestore, so that subsequent backward FETCHs
385 : * can be processed. Otherwise, store only the not-yet-fetched rows.
386 : * (The latter is not only more efficient, but avoids semantic
387 : * problems if the query's output isn't stable.)
388 : *
389 : * In the no-scroll case, tuple indexes in the tuplestore will not
390 : * match the cursor's nominal position (portalPos). Currently this
391 : * causes no difficulty because we only navigate in the tuplestore by
392 : * relative position, except for the tuplestore_skiptuples call below
393 : * and the tuplestore_rescan call in DoPortalRewind, both of which are
394 : * disabled for no-scroll cursors. But someday we might need to track
395 : * the offset between the holdStore and the cursor's nominal position
396 : * explicitly.
397 : */
398 82 : if (portal->cursorOptions & CURSOR_OPT_SCROLL)
399 : {
400 40 : ExecutorRewind(queryDesc);
401 : }
402 : else
403 : {
404 : /*
405 : * If we already reached end-of-query, set the direction to
406 : * NoMovement to avoid trying to fetch any tuples. (This check
407 : * exists because not all plan node types are robust about being
408 : * called again if they've already returned NULL once.) We'll
409 : * still set up an empty tuplestore, though, to keep this from
410 : * being a special case later.
411 : */
412 42 : if (portal->atEnd)
413 0 : direction = NoMovementScanDirection;
414 : }
415 :
416 : /*
417 : * Change the destination to output to the tuplestore. Note we tell
418 : * the tuplestore receiver to detoast all data passed through it; this
419 : * makes it safe to not keep a snapshot associated with the data.
420 : */
421 82 : queryDesc->dest = CreateDestReceiver(DestTuplestore);
422 82 : SetTuplestoreDestReceiverParams(queryDesc->dest,
423 : portal->holdStore,
424 : portal->holdContext,
425 : true,
426 : NULL,
427 : NULL);
428 :
429 : /* Fetch the result set into the tuplestore */
430 82 : ExecutorRun(queryDesc, direction, 0);
431 :
432 78 : queryDesc->dest->rDestroy(queryDesc->dest);
433 78 : queryDesc->dest = NULL;
434 :
435 : /*
436 : * Now shut down the inner executor.
437 : */
438 78 : portal->queryDesc = NULL; /* prevent double shutdown */
439 78 : ExecutorFinish(queryDesc);
440 78 : ExecutorEnd(queryDesc);
441 78 : FreeQueryDesc(queryDesc);
442 :
443 : /*
444 : * Set the position in the result set.
445 : */
446 78 : MemoryContextSwitchTo(portal->holdContext);
447 :
448 78 : if (portal->atEnd)
449 : {
450 : /*
451 : * Just force the tuplestore forward to its end. The size of the
452 : * skip request here is arbitrary.
453 : */
454 0 : while (tuplestore_skiptuples(portal->holdStore, 1000000, true))
455 : /* continue */ ;
456 : }
457 : else
458 : {
459 78 : tuplestore_rescan(portal->holdStore);
460 :
461 : /*
462 : * In the no-scroll case, the start of the tuplestore is exactly
463 : * where we want to be, so no repositioning is wanted.
464 : */
465 78 : if (portal->cursorOptions & CURSOR_OPT_SCROLL)
466 : {
467 40 : if (!tuplestore_skiptuples(portal->holdStore,
468 40 : portal->portalPos,
469 : true))
470 0 : elog(ERROR, "unexpected end of tuple stream");
471 : }
472 : }
473 : }
474 4 : PG_CATCH();
475 : {
476 : /* Uncaught error while executing portal: mark it dead */
477 4 : MarkPortalFailed(portal);
478 :
479 : /* Restore global vars and propagate error */
480 4 : ActivePortal = saveActivePortal;
481 4 : CurrentResourceOwner = saveResourceOwner;
482 4 : PortalContext = savePortalContext;
483 :
484 4 : PG_RE_THROW();
485 : }
486 78 : PG_END_TRY();
487 :
488 78 : MemoryContextSwitchTo(oldcxt);
489 :
490 : /* Mark portal not active */
491 78 : portal->status = PORTAL_READY;
492 :
493 78 : ActivePortal = saveActivePortal;
494 78 : CurrentResourceOwner = saveResourceOwner;
495 78 : PortalContext = savePortalContext;
496 :
497 78 : PopActiveSnapshot();
498 :
499 : /*
500 : * We can now release any subsidiary memory of the portal's context; we'll
501 : * never use it again. The executor already dropped its context, but this
502 : * will clean up anything that glommed onto the portal's context via
503 : * PortalContext.
504 : */
505 78 : MemoryContextDeleteChildren(portal->portalContext);
506 78 : }
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