Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * parallel_slot.c
4 : * Parallel support for front-end parallel database connections
5 : *
6 : *
7 : * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
8 : * Portions Copyright (c) 1994, Regents of the University of California
9 : *
10 : * src/fe_utils/parallel_slot.c
11 : *
12 : *-------------------------------------------------------------------------
13 : */
14 :
15 : #if defined(WIN32) && FD_SETSIZE < 1024
16 : #error FD_SETSIZE needs to have been increased
17 : #endif
18 :
19 : #include "postgres_fe.h"
20 :
21 : #include <sys/select.h>
22 :
23 : #include "common/logging.h"
24 : #include "fe_utils/cancel.h"
25 : #include "fe_utils/parallel_slot.h"
26 : #include "fe_utils/query_utils.h"
27 :
28 : #define ERRCODE_UNDEFINED_TABLE "42P01"
29 :
30 : static int select_loop(int maxFd, fd_set *workerset);
31 : static bool processQueryResult(ParallelSlot *slot, PGresult *result);
32 :
33 : /*
34 : * Process (and delete) a query result. Returns true if there's no problem,
35 : * false otherwise. It's up to the handler to decide what constitutes a
36 : * problem.
37 : */
38 : static bool
39 0 : processQueryResult(ParallelSlot *slot, PGresult *result)
40 : {
41 0 : Assert(slot->handler != NULL);
42 :
43 : /* On failure, the handler should return NULL after freeing the result */
44 0 : if (!slot->handler(result, slot->connection, slot->handler_context))
45 0 : return false;
46 :
47 : /* Ok, we have to free it ourself */
48 0 : PQclear(result);
49 0 : return true;
50 0 : }
51 :
52 : /*
53 : * Consume all the results generated for the given connection until
54 : * nothing remains. If at least one error is encountered, return false.
55 : * Note that this will block if the connection is busy.
56 : */
57 : static bool
58 0 : consumeQueryResult(ParallelSlot *slot)
59 : {
60 0 : bool ok = true;
61 0 : PGresult *result;
62 :
63 0 : SetCancelConn(slot->connection);
64 0 : while ((result = PQgetResult(slot->connection)) != NULL)
65 : {
66 0 : if (!processQueryResult(slot, result))
67 0 : ok = false;
68 : }
69 0 : ResetCancelConn();
70 0 : return ok;
71 0 : }
72 :
73 : /*
74 : * Wait until a file descriptor from the given set becomes readable.
75 : *
76 : * Returns the number of ready descriptors, or -1 on failure (including
77 : * getting a cancel request).
78 : */
79 : static int
80 0 : select_loop(int maxFd, fd_set *workerset)
81 : {
82 0 : int i;
83 0 : fd_set saveSet = *workerset;
84 :
85 0 : if (CancelRequested)
86 0 : return -1;
87 :
88 0 : for (;;)
89 : {
90 : /*
91 : * On Windows, we need to check once in a while for cancel requests;
92 : * on other platforms we rely on select() returning when interrupted.
93 : */
94 0 : struct timeval *tvp;
95 : #ifdef WIN32
96 : struct timeval tv = {0, 1000000};
97 :
98 : tvp = &tv;
99 : #else
100 0 : tvp = NULL;
101 : #endif
102 :
103 0 : *workerset = saveSet;
104 0 : i = select(maxFd + 1, workerset, NULL, NULL, tvp);
105 :
106 : #ifdef WIN32
107 : if (i == SOCKET_ERROR)
108 : {
109 : i = -1;
110 :
111 : if (WSAGetLastError() == WSAEINTR)
112 : errno = EINTR;
113 : }
114 : #endif
115 :
116 0 : if (i < 0 && errno == EINTR)
117 0 : continue; /* ignore this */
118 0 : if (i < 0 || CancelRequested)
119 0 : return -1; /* but not this */
120 0 : if (i == 0)
121 0 : continue; /* timeout (Win32 only) */
122 0 : break;
123 0 : }
124 :
125 0 : return i;
126 0 : }
127 :
128 : /*
129 : * Return the offset of a suitable idle slot, or -1 if none are available. If
130 : * the given dbname is not null, only idle slots connected to the given
131 : * database are considered suitable, otherwise all idle connected slots are
132 : * considered suitable.
133 : */
134 : static int
135 0 : find_matching_idle_slot(const ParallelSlotArray *sa, const char *dbname)
136 : {
137 0 : int i;
138 :
139 0 : for (i = 0; i < sa->numslots; i++)
140 : {
141 0 : if (sa->slots[i].inUse)
142 0 : continue;
143 :
144 0 : if (sa->slots[i].connection == NULL)
145 0 : continue;
146 :
147 0 : if (dbname == NULL ||
148 0 : strcmp(PQdb(sa->slots[i].connection), dbname) == 0)
149 0 : return i;
150 0 : }
151 0 : return -1;
152 0 : }
153 :
154 : /*
155 : * Return the offset of the first slot without a database connection, or -1 if
156 : * all slots are connected.
157 : */
158 : static int
159 0 : find_unconnected_slot(const ParallelSlotArray *sa)
160 : {
161 0 : int i;
162 :
163 0 : for (i = 0; i < sa->numslots; i++)
164 : {
165 0 : if (sa->slots[i].inUse)
166 0 : continue;
167 :
168 0 : if (sa->slots[i].connection == NULL)
169 0 : return i;
170 0 : }
171 :
172 0 : return -1;
173 0 : }
174 :
175 : /*
176 : * Return the offset of the first idle slot, or -1 if all slots are busy.
177 : */
178 : static int
179 0 : find_any_idle_slot(const ParallelSlotArray *sa)
180 : {
181 0 : int i;
182 :
183 0 : for (i = 0; i < sa->numslots; i++)
184 0 : if (!sa->slots[i].inUse)
185 0 : return i;
186 :
187 0 : return -1;
188 0 : }
189 :
190 : /*
191 : * Wait for any slot's connection to have query results, consume the results,
192 : * and update the slot's status as appropriate. Returns true on success,
193 : * false on cancellation, on error, or if no slots are connected.
194 : */
195 : static bool
196 0 : wait_on_slots(ParallelSlotArray *sa)
197 : {
198 0 : int i;
199 0 : fd_set slotset;
200 0 : int maxFd = 0;
201 0 : PGconn *cancelconn = NULL;
202 :
203 : /* We must reconstruct the fd_set for each call to select_loop */
204 0 : FD_ZERO(&slotset);
205 :
206 0 : for (i = 0; i < sa->numslots; i++)
207 : {
208 0 : int sock;
209 :
210 : /* We shouldn't get here if we still have slots without connections */
211 0 : Assert(sa->slots[i].connection != NULL);
212 :
213 0 : sock = PQsocket(sa->slots[i].connection);
214 :
215 : /*
216 : * We don't really expect any connections to lose their sockets after
217 : * startup, but just in case, cope by ignoring them.
218 : */
219 0 : if (sock < 0)
220 0 : continue;
221 :
222 : /* Keep track of the first valid connection we see. */
223 0 : if (cancelconn == NULL)
224 0 : cancelconn = sa->slots[i].connection;
225 :
226 0 : FD_SET(sock, &slotset);
227 0 : if (sock > maxFd)
228 0 : maxFd = sock;
229 0 : }
230 :
231 : /*
232 : * If we get this far with no valid connections, processing cannot
233 : * continue.
234 : */
235 0 : if (cancelconn == NULL)
236 0 : return false;
237 :
238 0 : SetCancelConn(cancelconn);
239 0 : i = select_loop(maxFd, &slotset);
240 0 : ResetCancelConn();
241 :
242 : /* failure? */
243 0 : if (i < 0)
244 0 : return false;
245 :
246 0 : for (i = 0; i < sa->numslots; i++)
247 : {
248 0 : int sock;
249 :
250 0 : sock = PQsocket(sa->slots[i].connection);
251 :
252 0 : if (sock >= 0 && FD_ISSET(sock, &slotset))
253 : {
254 : /* select() says input is available, so consume it */
255 0 : PQconsumeInput(sa->slots[i].connection);
256 0 : }
257 :
258 : /* Collect result(s) as long as any are available */
259 0 : while (!PQisBusy(sa->slots[i].connection))
260 : {
261 0 : PGresult *result = PQgetResult(sa->slots[i].connection);
262 :
263 0 : if (result != NULL)
264 : {
265 : /* Handle and discard the command result */
266 0 : if (!processQueryResult(&sa->slots[i], result))
267 0 : return false;
268 0 : }
269 : else
270 : {
271 : /* This connection has become idle */
272 0 : ParallelSlotSetIdle(&sa->slots[i]);
273 0 : break;
274 : }
275 0 : }
276 0 : }
277 0 : return true;
278 0 : }
279 :
280 : /*
281 : * Open a new database connection using the stored connection parameters and
282 : * optionally a given dbname if not null, execute the stored initial command if
283 : * any, and associate the new connection with the given slot.
284 : */
285 : static void
286 0 : connect_slot(ParallelSlotArray *sa, int slotno, const char *dbname)
287 : {
288 0 : const char *old_override;
289 0 : ParallelSlot *slot = &sa->slots[slotno];
290 :
291 0 : old_override = sa->cparams->override_dbname;
292 0 : if (dbname)
293 0 : sa->cparams->override_dbname = dbname;
294 0 : slot->connection = connectDatabase(sa->cparams, sa->progname, sa->echo, false, true);
295 0 : sa->cparams->override_dbname = old_override;
296 :
297 : /*
298 : * POSIX defines FD_SETSIZE as the highest file descriptor acceptable to
299 : * FD_SET() and allied macros. Windows defines it as a ceiling on the
300 : * count of file descriptors in the set, not a ceiling on the value of
301 : * each file descriptor; see
302 : * https://learn.microsoft.com/en-us/windows/win32/api/winsock2/nf-winsock2-select
303 : * and
304 : * https://learn.microsoft.com/en-us/windows/win32/api/winsock/ns-winsock-fd_set.
305 : * We can't ignore that, because Windows starts file descriptors at a
306 : * higher value, delays reuse, and skips values. With less than ten
307 : * concurrent file descriptors, opened and closed rapidly, one can reach
308 : * file descriptor 1024.
309 : *
310 : * Doing a hard exit here is a bit grotty, but it doesn't seem worth
311 : * complicating the API to make it less grotty.
312 : */
313 : #ifdef WIN32
314 : if (slotno >= FD_SETSIZE)
315 : {
316 : pg_log_error("too many jobs for this platform: %d", slotno);
317 : exit(1);
318 : }
319 : #else
320 : {
321 0 : int fd = PQsocket(slot->connection);
322 :
323 0 : if (fd >= FD_SETSIZE)
324 : {
325 0 : pg_log_error("socket file descriptor out of range for select(): %d",
326 : fd);
327 0 : pg_log_error_hint("Try fewer jobs.");
328 0 : exit(1);
329 : }
330 0 : }
331 : #endif
332 :
333 : /* Setup the connection using the supplied command, if any. */
334 0 : if (sa->initcmd)
335 0 : executeCommand(slot->connection, sa->initcmd, sa->echo);
336 0 : }
337 :
338 : /*
339 : * ParallelSlotsGetIdle
340 : * Return a connection slot that is ready to execute a command.
341 : *
342 : * The slot returned is chosen as follows:
343 : *
344 : * If any idle slot already has an open connection, and if either dbname is
345 : * null or the existing connection is to the given database, that slot will be
346 : * returned allowing the connection to be reused.
347 : *
348 : * Otherwise, if any idle slot is not yet connected to any database, the slot
349 : * will be returned with its connection opened using the stored cparams and
350 : * optionally the given dbname if not null.
351 : *
352 : * Otherwise, if any idle slot exists, an idle slot will be chosen and returned
353 : * after having its connection disconnected and reconnected using the stored
354 : * cparams and optionally the given dbname if not null.
355 : *
356 : * Otherwise, if any slots have connections that are busy, we loop on select()
357 : * until one socket becomes available. When this happens, we read the whole
358 : * set and mark as free all sockets that become available. We then select a
359 : * slot using the same rules as above.
360 : *
361 : * Otherwise, we cannot return a slot, which is an error, and NULL is returned.
362 : *
363 : * For any connection created, if the stored initcmd is not null, it will be
364 : * executed as a command on the newly formed connection before the slot is
365 : * returned.
366 : *
367 : * If an error occurs, NULL is returned.
368 : */
369 : ParallelSlot *
370 0 : ParallelSlotsGetIdle(ParallelSlotArray *sa, const char *dbname)
371 : {
372 0 : int offset;
373 :
374 0 : Assert(sa);
375 0 : Assert(sa->numslots > 0);
376 :
377 0 : while (1)
378 : {
379 : /* First choice: a slot already connected to the desired database. */
380 0 : offset = find_matching_idle_slot(sa, dbname);
381 0 : if (offset >= 0)
382 : {
383 0 : sa->slots[offset].inUse = true;
384 0 : return &sa->slots[offset];
385 : }
386 :
387 : /* Second choice: a slot not connected to any database. */
388 0 : offset = find_unconnected_slot(sa);
389 0 : if (offset >= 0)
390 : {
391 0 : connect_slot(sa, offset, dbname);
392 0 : sa->slots[offset].inUse = true;
393 0 : return &sa->slots[offset];
394 : }
395 :
396 : /* Third choice: a slot connected to the wrong database. */
397 0 : offset = find_any_idle_slot(sa);
398 0 : if (offset >= 0)
399 : {
400 0 : disconnectDatabase(sa->slots[offset].connection);
401 0 : sa->slots[offset].connection = NULL;
402 0 : connect_slot(sa, offset, dbname);
403 0 : sa->slots[offset].inUse = true;
404 0 : return &sa->slots[offset];
405 : }
406 :
407 : /*
408 : * Fourth choice: block until one or more slots become available. If
409 : * any slots hit a fatal error, we'll find out about that here and
410 : * return NULL.
411 : */
412 0 : if (!wait_on_slots(sa))
413 0 : return NULL;
414 : }
415 0 : }
416 :
417 : /*
418 : * ParallelSlotsSetup
419 : * Prepare a set of parallel slots but do not connect to any database.
420 : *
421 : * This creates and initializes a set of slots, marking all parallel slots as
422 : * free and ready to use. Establishing connections is delayed until requesting
423 : * a free slot. The cparams, progname, echo, and initcmd are stored for later
424 : * use and must remain valid for the lifetime of the returned array.
425 : */
426 : ParallelSlotArray *
427 0 : ParallelSlotsSetup(int numslots, ConnParams *cparams, const char *progname,
428 : bool echo, const char *initcmd)
429 : {
430 0 : ParallelSlotArray *sa;
431 :
432 0 : Assert(numslots > 0);
433 0 : Assert(cparams != NULL);
434 0 : Assert(progname != NULL);
435 :
436 0 : sa = (ParallelSlotArray *) palloc0(offsetof(ParallelSlotArray, slots) +
437 0 : numslots * sizeof(ParallelSlot));
438 :
439 0 : sa->numslots = numslots;
440 0 : sa->cparams = cparams;
441 0 : sa->progname = progname;
442 0 : sa->echo = echo;
443 0 : sa->initcmd = initcmd;
444 :
445 0 : return sa;
446 0 : }
447 :
448 : /*
449 : * ParallelSlotsAdoptConn
450 : * Assign an open connection to the slots array for reuse.
451 : *
452 : * This turns over ownership of an open connection to a slots array. The
453 : * caller should not further use or close the connection. All the connection's
454 : * parameters (user, host, port, etc.) except possibly dbname should match
455 : * those of the slots array's cparams, as given in ParallelSlotsSetup. If
456 : * these parameters differ, subsequent behavior is undefined.
457 : */
458 : void
459 0 : ParallelSlotsAdoptConn(ParallelSlotArray *sa, PGconn *conn)
460 : {
461 0 : int offset;
462 :
463 0 : offset = find_unconnected_slot(sa);
464 0 : if (offset >= 0)
465 0 : sa->slots[offset].connection = conn;
466 : else
467 0 : disconnectDatabase(conn);
468 0 : }
469 :
470 : /*
471 : * ParallelSlotsTerminate
472 : * Clean up a set of parallel slots
473 : *
474 : * Iterate through all connections in a given set of ParallelSlots and
475 : * terminate all connections.
476 : */
477 : void
478 0 : ParallelSlotsTerminate(ParallelSlotArray *sa)
479 : {
480 0 : int i;
481 :
482 0 : for (i = 0; i < sa->numslots; i++)
483 : {
484 0 : PGconn *conn = sa->slots[i].connection;
485 :
486 0 : if (conn == NULL)
487 0 : continue;
488 :
489 0 : disconnectDatabase(conn);
490 0 : }
491 0 : }
492 :
493 : /*
494 : * ParallelSlotsWaitCompletion
495 : *
496 : * Wait for all connections to finish, returning false if at least one
497 : * error has been found on the way.
498 : */
499 : bool
500 0 : ParallelSlotsWaitCompletion(ParallelSlotArray *sa)
501 : {
502 0 : int i;
503 :
504 0 : for (i = 0; i < sa->numslots; i++)
505 : {
506 0 : if (sa->slots[i].connection == NULL)
507 0 : continue;
508 0 : if (!consumeQueryResult(&sa->slots[i]))
509 0 : return false;
510 : /* Mark connection as idle */
511 0 : ParallelSlotSetIdle(&sa->slots[i]);
512 0 : }
513 :
514 0 : return true;
515 0 : }
516 :
517 : /*
518 : * TableCommandResultHandler
519 : *
520 : * ParallelSlotResultHandler for results of commands (not queries) against
521 : * tables.
522 : *
523 : * Requires that the result status is either PGRES_COMMAND_OK or an error about
524 : * a missing table. This is useful for utilities that compile a list of tables
525 : * to process and then run commands (vacuum, reindex, or whatever) against
526 : * those tables, as there is a race condition between the time the list is
527 : * compiled and the time the command attempts to open the table.
528 : *
529 : * For missing tables, logs an error but allows processing to continue.
530 : *
531 : * For all other errors, logs an error and terminates further processing.
532 : *
533 : * res: PGresult from the query executed on the slot's connection
534 : * conn: connection belonging to the slot
535 : * context: unused
536 : */
537 : bool
538 0 : TableCommandResultHandler(PGresult *res, PGconn *conn, void *context)
539 : {
540 0 : Assert(res != NULL);
541 0 : Assert(conn != NULL);
542 :
543 : /*
544 : * If it's an error, report it. Errors about a missing table are harmless
545 : * so we continue processing; but die for other errors.
546 : */
547 0 : if (PQresultStatus(res) != PGRES_COMMAND_OK)
548 : {
549 0 : char *sqlState = PQresultErrorField(res, PG_DIAG_SQLSTATE);
550 :
551 0 : pg_log_error("processing of database \"%s\" failed: %s",
552 : PQdb(conn), PQerrorMessage(conn));
553 :
554 0 : if (sqlState && strcmp(sqlState, ERRCODE_UNDEFINED_TABLE) != 0)
555 : {
556 0 : PQclear(res);
557 0 : return false;
558 : }
559 0 : }
560 :
561 0 : return true;
562 0 : }
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