1/*-------------------------------------------------------------------------
2 *
3 * parallel.c
4 * Infrastructure for launching parallel workers
5 *
6 * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
7 * Portions Copyright (c) 1994, Regents of the University of California
8 *
9 * IDENTIFICATION
10 * src/backend/access/transam/parallel.c
11 *
12 *-------------------------------------------------------------------------
13 */
14
15#include "postgres.h"
16
17#include "access/nbtree.h"
18#include "access/parallel.h"
19#include "access/session.h"
20#include "access/xact.h"
21#include "access/xlog.h"
22#include "catalog/pg_enum.h"
23#include "catalog/index.h"
24#include "catalog/namespace.h"
25#include "commands/async.h"
26#include "executor/execParallel.h"
27#include "libpq/libpq.h"
28#include "libpq/pqformat.h"
29#include "libpq/pqmq.h"
30#include "miscadmin.h"
31#include "optimizer/optimizer.h"
32#include "pgstat.h"
33#include "storage/ipc.h"
34#include "storage/predicate.h"
35#include "storage/sinval.h"
36#include "storage/spin.h"
37#include "tcop/tcopprot.h"
38#include "utils/combocid.h"
39#include "utils/guc.h"
40#include "utils/inval.h"
41#include "utils/memutils.h"
42#include "utils/relmapper.h"
43#include "utils/snapmgr.h"
44#include "utils/typcache.h"
45
46
47/*
48 * We don't want to waste a lot of memory on an error queue which, most of
49 * the time, will process only a handful of small messages. However, it is
50 * desirable to make it large enough that a typical ErrorResponse can be sent
51 * without blocking. That way, a worker that errors out can write the whole
52 * message into the queue and terminate without waiting for the user backend.
53 */
54#define PARALLEL_ERROR_QUEUE_SIZE 16384
55
56/* Magic number for parallel context TOC. */
57#define PARALLEL_MAGIC 0x50477c7c
58
59/*
60 * Magic numbers for per-context parallel state sharing. Higher-level code
61 * should use smaller values, leaving these very large ones for use by this
62 * module.
63 */
64#define PARALLEL_KEY_FIXED UINT64CONST(0xFFFFFFFFFFFF0001)
65#define PARALLEL_KEY_ERROR_QUEUE UINT64CONST(0xFFFFFFFFFFFF0002)
66#define PARALLEL_KEY_LIBRARY UINT64CONST(0xFFFFFFFFFFFF0003)
67#define PARALLEL_KEY_GUC UINT64CONST(0xFFFFFFFFFFFF0004)
68#define PARALLEL_KEY_COMBO_CID UINT64CONST(0xFFFFFFFFFFFF0005)
69#define PARALLEL_KEY_TRANSACTION_SNAPSHOT UINT64CONST(0xFFFFFFFFFFFF0006)
70#define PARALLEL_KEY_ACTIVE_SNAPSHOT UINT64CONST(0xFFFFFFFFFFFF0007)
71#define PARALLEL_KEY_TRANSACTION_STATE UINT64CONST(0xFFFFFFFFFFFF0008)
72#define PARALLEL_KEY_ENTRYPOINT UINT64CONST(0xFFFFFFFFFFFF0009)
73#define PARALLEL_KEY_SESSION_DSM UINT64CONST(0xFFFFFFFFFFFF000A)
74#define PARALLEL_KEY_REINDEX_STATE UINT64CONST(0xFFFFFFFFFFFF000B)
75#define PARALLEL_KEY_RELMAPPER_STATE UINT64CONST(0xFFFFFFFFFFFF000C)
76#define PARALLEL_KEY_ENUMBLACKLIST UINT64CONST(0xFFFFFFFFFFFF000D)
77
78/* Fixed-size parallel state. */
79typedef struct FixedParallelState
80{
81 /* Fixed-size state that workers must restore. */
82 Oid database_id;
83 Oid authenticated_user_id;
84 Oid current_user_id;
85 Oid outer_user_id;
86 Oid temp_namespace_id;
87 Oid temp_toast_namespace_id;
88 int sec_context;
89 bool is_superuser;
90 PGPROC *parallel_master_pgproc;
91 pid_t parallel_master_pid;
92 BackendId parallel_master_backend_id;
93 TimestampTz xact_ts;
94 TimestampTz stmt_ts;
95 SerializableXactHandle serializable_xact_handle;
96
97 /* Mutex protects remaining fields. */
98 slock_t mutex;
99
100 /* Maximum XactLastRecEnd of any worker. */
101 XLogRecPtr last_xlog_end;
102} FixedParallelState;
103
104/*
105 * Our parallel worker number. We initialize this to -1, meaning that we are
106 * not a parallel worker. In parallel workers, it will be set to a value >= 0
107 * and < the number of workers before any user code is invoked; each parallel
108 * worker will get a different parallel worker number.
109 */
110int ParallelWorkerNumber = -1;
111
112/* Is there a parallel message pending which we need to receive? */
113volatile bool ParallelMessagePending = false;
114
115/* Are we initializing a parallel worker? */
116bool InitializingParallelWorker = false;
117
118/* Pointer to our fixed parallel state. */
119static FixedParallelState *MyFixedParallelState;
120
121/* List of active parallel contexts. */
122static dlist_head pcxt_list = DLIST_STATIC_INIT(pcxt_list);
123
124/* Backend-local copy of data from FixedParallelState. */
125static pid_t ParallelMasterPid;
126
127/*
128 * List of internal parallel worker entry points. We need this for
129 * reasons explained in LookupParallelWorkerFunction(), below.
130 */
131static const struct
132{
133 const char *fn_name;
134 parallel_worker_main_type fn_addr;
135} InternalParallelWorkers[] =
136
137{
138 {
139 "ParallelQueryMain", ParallelQueryMain
140 },
141 {
142 "_bt_parallel_build_main", _bt_parallel_build_main
143 }
144};
145
146/* Private functions. */
147static void HandleParallelMessage(ParallelContext *pcxt, int i, StringInfo msg);
148static void WaitForParallelWorkersToExit(ParallelContext *pcxt);
149static parallel_worker_main_type LookupParallelWorkerFunction(const char *libraryname, const char *funcname);
150static void ParallelWorkerShutdown(int code, Datum arg);
151
152
153/*
154 * Establish a new parallel context. This should be done after entering
155 * parallel mode, and (unless there is an error) the context should be
156 * destroyed before exiting the current subtransaction.
157 */
158ParallelContext *
159CreateParallelContext(const char *library_name, const char *function_name,
160 int nworkers)
161{
162 MemoryContext oldcontext;
163 ParallelContext *pcxt;
164
165 /* It is unsafe to create a parallel context if not in parallel mode. */
166 Assert(IsInParallelMode());
167
168 /* Number of workers should be non-negative. */
169 Assert(nworkers >= 0);
170
171 /* We might be running in a short-lived memory context. */
172 oldcontext = MemoryContextSwitchTo(TopTransactionContext);
173
174 /* Initialize a new ParallelContext. */
175 pcxt = palloc0(sizeof(ParallelContext));
176 pcxt->subid = GetCurrentSubTransactionId();
177 pcxt->nworkers = nworkers;
178 pcxt->library_name = pstrdup(library_name);
179 pcxt->function_name = pstrdup(function_name);
180 pcxt->error_context_stack = error_context_stack;
181 shm_toc_initialize_estimator(&pcxt->estimator);
182 dlist_push_head(&pcxt_list, &pcxt->node);
183
184 /* Restore previous memory context. */
185 MemoryContextSwitchTo(oldcontext);
186
187 return pcxt;
188}
189
190/*
191 * Establish the dynamic shared memory segment for a parallel context and
192 * copy state and other bookkeeping information that will be needed by
193 * parallel workers into it.
194 */
195void
196InitializeParallelDSM(ParallelContext *pcxt)
197{
198 MemoryContext oldcontext;
199 Size library_len = 0;
200 Size guc_len = 0;
201 Size combocidlen = 0;
202 Size tsnaplen = 0;
203 Size asnaplen = 0;
204 Size tstatelen = 0;
205 Size reindexlen = 0;
206 Size relmapperlen = 0;
207 Size enumblacklistlen = 0;
208 Size segsize = 0;
209 int i;
210 FixedParallelState *fps;
211 dsm_handle session_dsm_handle = DSM_HANDLE_INVALID;
212 Snapshot transaction_snapshot = GetTransactionSnapshot();
213 Snapshot active_snapshot = GetActiveSnapshot();
214
215 /* We might be running in a very short-lived memory context. */
216 oldcontext = MemoryContextSwitchTo(TopTransactionContext);
217
218 /* Allow space to store the fixed-size parallel state. */
219 shm_toc_estimate_chunk(&pcxt->estimator, sizeof(FixedParallelState));
220 shm_toc_estimate_keys(&pcxt->estimator, 1);
221
222 /*
223 * Normally, the user will have requested at least one worker process, but
224 * if by chance they have not, we can skip a bunch of things here.
225 */
226 if (pcxt->nworkers > 0)
227 {
228 /* Get (or create) the per-session DSM segment's handle. */
229 session_dsm_handle = GetSessionDsmHandle();
230
231 /*
232 * If we weren't able to create a per-session DSM segment, then we can
233 * continue but we can't safely launch any workers because their
234 * record typmods would be incompatible so they couldn't exchange
235 * tuples.
236 */
237 if (session_dsm_handle == DSM_HANDLE_INVALID)
238 pcxt->nworkers = 0;
239 }
240
241 if (pcxt->nworkers > 0)
242 {
243 /* Estimate space for various kinds of state sharing. */
244 library_len = EstimateLibraryStateSpace();
245 shm_toc_estimate_chunk(&pcxt->estimator, library_len);
246 guc_len = EstimateGUCStateSpace();
247 shm_toc_estimate_chunk(&pcxt->estimator, guc_len);
248 combocidlen = EstimateComboCIDStateSpace();
249 shm_toc_estimate_chunk(&pcxt->estimator, combocidlen);
250 tsnaplen = EstimateSnapshotSpace(transaction_snapshot);
251 shm_toc_estimate_chunk(&pcxt->estimator, tsnaplen);
252 asnaplen = EstimateSnapshotSpace(active_snapshot);
253 shm_toc_estimate_chunk(&pcxt->estimator, asnaplen);
254 tstatelen = EstimateTransactionStateSpace();
255 shm_toc_estimate_chunk(&pcxt->estimator, tstatelen);
256 shm_toc_estimate_chunk(&pcxt->estimator, sizeof(dsm_handle));
257 reindexlen = EstimateReindexStateSpace();
258 shm_toc_estimate_chunk(&pcxt->estimator, reindexlen);
259 relmapperlen = EstimateRelationMapSpace();
260 shm_toc_estimate_chunk(&pcxt->estimator, relmapperlen);
261 enumblacklistlen = EstimateEnumBlacklistSpace();
262 shm_toc_estimate_chunk(&pcxt->estimator, enumblacklistlen);
263 /* If you add more chunks here, you probably need to add keys. */
264 shm_toc_estimate_keys(&pcxt->estimator, 10);
265
266 /* Estimate space need for error queues. */
267 StaticAssertStmt(BUFFERALIGN(PARALLEL_ERROR_QUEUE_SIZE) ==
268 PARALLEL_ERROR_QUEUE_SIZE,
269 "parallel error queue size not buffer-aligned");
270 shm_toc_estimate_chunk(&pcxt->estimator,
271 mul_size(PARALLEL_ERROR_QUEUE_SIZE,
272 pcxt->nworkers));
273 shm_toc_estimate_keys(&pcxt->estimator, 1);
274
275 /* Estimate how much we'll need for the entrypoint info. */
276 shm_toc_estimate_chunk(&pcxt->estimator, strlen(pcxt->library_name) +
277 strlen(pcxt->function_name) + 2);
278 shm_toc_estimate_keys(&pcxt->estimator, 1);
279 }
280
281 /*
282 * Create DSM and initialize with new table of contents. But if the user
283 * didn't request any workers, then don't bother creating a dynamic shared
284 * memory segment; instead, just use backend-private memory.
285 *
286 * Also, if we can't create a dynamic shared memory segment because the
287 * maximum number of segments have already been created, then fall back to
288 * backend-private memory, and plan not to use any workers. We hope this
289 * won't happen very often, but it's better to abandon the use of
290 * parallelism than to fail outright.
291 */
292 segsize = shm_toc_estimate(&pcxt->estimator);
293 if (pcxt->nworkers > 0)
294 pcxt->seg = dsm_create(segsize, DSM_CREATE_NULL_IF_MAXSEGMENTS);
295 if (pcxt->seg != NULL)
296 pcxt->toc = shm_toc_create(PARALLEL_MAGIC,
297 dsm_segment_address(pcxt->seg),
298 segsize);
299 else
300 {
301 pcxt->nworkers = 0;
302 pcxt->private_memory = MemoryContextAlloc(TopMemoryContext, segsize);
303 pcxt->toc = shm_toc_create(PARALLEL_MAGIC, pcxt->private_memory,
304 segsize);
305 }
306
307 /* Initialize fixed-size state in shared memory. */
308 fps = (FixedParallelState *)
309 shm_toc_allocate(pcxt->toc, sizeof(FixedParallelState));
310 fps->database_id = MyDatabaseId;
311 fps->authenticated_user_id = GetAuthenticatedUserId();
312 fps->outer_user_id = GetCurrentRoleId();
313 fps->is_superuser = session_auth_is_superuser;
314 GetUserIdAndSecContext(&fps->current_user_id, &fps->sec_context);
315 GetTempNamespaceState(&fps->temp_namespace_id,
316 &fps->temp_toast_namespace_id);
317 fps->parallel_master_pgproc = MyProc;
318 fps->parallel_master_pid = MyProcPid;
319 fps->parallel_master_backend_id = MyBackendId;
320 fps->xact_ts = GetCurrentTransactionStartTimestamp();
321 fps->stmt_ts = GetCurrentStatementStartTimestamp();
322 fps->serializable_xact_handle = ShareSerializableXact();
323 SpinLockInit(&fps->mutex);
324 fps->last_xlog_end = 0;
325 shm_toc_insert(pcxt->toc, PARALLEL_KEY_FIXED, fps);
326
327 /* We can skip the rest of this if we're not budgeting for any workers. */
328 if (pcxt->nworkers > 0)
329 {
330 char *libraryspace;
331 char *gucspace;
332 char *combocidspace;
333 char *tsnapspace;
334 char *asnapspace;
335 char *tstatespace;
336 char *reindexspace;
337 char *relmapperspace;
338 char *error_queue_space;
339 char *session_dsm_handle_space;
340 char *entrypointstate;
341 char *enumblacklistspace;
342 Size lnamelen;
343
344 /* Serialize shared libraries we have loaded. */
345 libraryspace = shm_toc_allocate(pcxt->toc, library_len);
346 SerializeLibraryState(library_len, libraryspace);
347 shm_toc_insert(pcxt->toc, PARALLEL_KEY_LIBRARY, libraryspace);
348
349 /* Serialize GUC settings. */
350 gucspace = shm_toc_allocate(pcxt->toc, guc_len);
351 SerializeGUCState(guc_len, gucspace);
352 shm_toc_insert(pcxt->toc, PARALLEL_KEY_GUC, gucspace);
353
354 /* Serialize combo CID state. */
355 combocidspace = shm_toc_allocate(pcxt->toc, combocidlen);
356 SerializeComboCIDState(combocidlen, combocidspace);
357 shm_toc_insert(pcxt->toc, PARALLEL_KEY_COMBO_CID, combocidspace);
358
359 /* Serialize transaction snapshot and active snapshot. */
360 tsnapspace = shm_toc_allocate(pcxt->toc, tsnaplen);
361 SerializeSnapshot(transaction_snapshot, tsnapspace);
362 shm_toc_insert(pcxt->toc, PARALLEL_KEY_TRANSACTION_SNAPSHOT,
363 tsnapspace);
364 asnapspace = shm_toc_allocate(pcxt->toc, asnaplen);
365 SerializeSnapshot(active_snapshot, asnapspace);
366 shm_toc_insert(pcxt->toc, PARALLEL_KEY_ACTIVE_SNAPSHOT, asnapspace);
367
368 /* Provide the handle for per-session segment. */
369 session_dsm_handle_space = shm_toc_allocate(pcxt->toc,
370 sizeof(dsm_handle));
371 *(dsm_handle *) session_dsm_handle_space = session_dsm_handle;
372 shm_toc_insert(pcxt->toc, PARALLEL_KEY_SESSION_DSM,
373 session_dsm_handle_space);
374
375 /* Serialize transaction state. */
376 tstatespace = shm_toc_allocate(pcxt->toc, tstatelen);
377 SerializeTransactionState(tstatelen, tstatespace);
378 shm_toc_insert(pcxt->toc, PARALLEL_KEY_TRANSACTION_STATE, tstatespace);
379
380 /* Serialize reindex state. */
381 reindexspace = shm_toc_allocate(pcxt->toc, reindexlen);
382 SerializeReindexState(reindexlen, reindexspace);
383 shm_toc_insert(pcxt->toc, PARALLEL_KEY_REINDEX_STATE, reindexspace);
384
385 /* Serialize relmapper state. */
386 relmapperspace = shm_toc_allocate(pcxt->toc, relmapperlen);
387 SerializeRelationMap(relmapperlen, relmapperspace);
388 shm_toc_insert(pcxt->toc, PARALLEL_KEY_RELMAPPER_STATE,
389 relmapperspace);
390
391 /* Serialize enum blacklist state. */
392 enumblacklistspace = shm_toc_allocate(pcxt->toc, enumblacklistlen);
393 SerializeEnumBlacklist(enumblacklistspace, enumblacklistlen);
394 shm_toc_insert(pcxt->toc, PARALLEL_KEY_ENUMBLACKLIST,
395 enumblacklistspace);
396
397 /* Allocate space for worker information. */
398 pcxt->worker = palloc0(sizeof(ParallelWorkerInfo) * pcxt->nworkers);
399
400 /*
401 * Establish error queues in dynamic shared memory.
402 *
403 * These queues should be used only for transmitting ErrorResponse,
404 * NoticeResponse, and NotifyResponse protocol messages. Tuple data
405 * should be transmitted via separate (possibly larger?) queues.
406 */
407 error_queue_space =
408 shm_toc_allocate(pcxt->toc,
409 mul_size(PARALLEL_ERROR_QUEUE_SIZE,
410 pcxt->nworkers));
411 for (i = 0; i < pcxt->nworkers; ++i)
412 {
413 char *start;
414 shm_mq *mq;
415
416 start = error_queue_space + i * PARALLEL_ERROR_QUEUE_SIZE;
417 mq = shm_mq_create(start, PARALLEL_ERROR_QUEUE_SIZE);
418 shm_mq_set_receiver(mq, MyProc);
419 pcxt->worker[i].error_mqh = shm_mq_attach(mq, pcxt->seg, NULL);
420 }
421 shm_toc_insert(pcxt->toc, PARALLEL_KEY_ERROR_QUEUE, error_queue_space);
422
423 /*
424 * Serialize entrypoint information. It's unsafe to pass function
425 * pointers across processes, as the function pointer may be different
426 * in each process in EXEC_BACKEND builds, so we always pass library
427 * and function name. (We use library name "postgres" for functions
428 * in the core backend.)
429 */
430 lnamelen = strlen(pcxt->library_name);
431 entrypointstate = shm_toc_allocate(pcxt->toc, lnamelen +
432 strlen(pcxt->function_name) + 2);
433 strcpy(entrypointstate, pcxt->library_name);
434 strcpy(entrypointstate + lnamelen + 1, pcxt->function_name);
435 shm_toc_insert(pcxt->toc, PARALLEL_KEY_ENTRYPOINT, entrypointstate);
436 }
437
438 /* Restore previous memory context. */
439 MemoryContextSwitchTo(oldcontext);
440}
441
442/*
443 * Reinitialize the dynamic shared memory segment for a parallel context such
444 * that we could launch workers for it again.
445 */
446void
447ReinitializeParallelDSM(ParallelContext *pcxt)
448{
449 FixedParallelState *fps;
450
451 /* Wait for any old workers to exit. */
452 if (pcxt->nworkers_launched > 0)
453 {
454 WaitForParallelWorkersToFinish(pcxt);
455 WaitForParallelWorkersToExit(pcxt);
456 pcxt->nworkers_launched = 0;
457 if (pcxt->known_attached_workers)
458 {
459 pfree(pcxt->known_attached_workers);
460 pcxt->known_attached_workers = NULL;
461 pcxt->nknown_attached_workers = 0;
462 }
463 }
464
465 /* Reset a few bits of fixed parallel state to a clean state. */
466 fps = shm_toc_lookup(pcxt->toc, PARALLEL_KEY_FIXED, false);
467 fps->last_xlog_end = 0;
468
469 /* Recreate error queues (if they exist). */
470 if (pcxt->nworkers > 0)
471 {
472 char *error_queue_space;
473 int i;
474
475 error_queue_space =
476 shm_toc_lookup(pcxt->toc, PARALLEL_KEY_ERROR_QUEUE, false);
477 for (i = 0; i < pcxt->nworkers; ++i)
478 {
479 char *start;
480 shm_mq *mq;
481
482 start = error_queue_space + i * PARALLEL_ERROR_QUEUE_SIZE;
483 mq = shm_mq_create(start, PARALLEL_ERROR_QUEUE_SIZE);
484 shm_mq_set_receiver(mq, MyProc);
485 pcxt->worker[i].error_mqh = shm_mq_attach(mq, pcxt->seg, NULL);
486 }
487 }
488}
489
490/*
491 * Launch parallel workers.
492 */
493void
494LaunchParallelWorkers(ParallelContext *pcxt)
495{
496 MemoryContext oldcontext;
497 BackgroundWorker worker;
498 int i;
499 bool any_registrations_failed = false;
500
501 /* Skip this if we have no workers. */
502 if (pcxt->nworkers == 0)
503 return;
504
505 /* We need to be a lock group leader. */
506 BecomeLockGroupLeader();
507
508 /* If we do have workers, we'd better have a DSM segment. */
509 Assert(pcxt->seg != NULL);
510
511 /* We might be running in a short-lived memory context. */
512 oldcontext = MemoryContextSwitchTo(TopTransactionContext);
513
514 /* Configure a worker. */
515 memset(&worker, 0, sizeof(worker));
516 snprintf(worker.bgw_name, BGW_MAXLEN, "parallel worker for PID %d",
517 MyProcPid);
518 snprintf(worker.bgw_type, BGW_MAXLEN, "parallel worker");
519 worker.bgw_flags =
520 BGWORKER_SHMEM_ACCESS | BGWORKER_BACKEND_DATABASE_CONNECTION
521 | BGWORKER_CLASS_PARALLEL;
522 worker.bgw_start_time = BgWorkerStart_ConsistentState;
523 worker.bgw_restart_time = BGW_NEVER_RESTART;
524 sprintf(worker.bgw_library_name, "postgres");
525 sprintf(worker.bgw_function_name, "ParallelWorkerMain");
526 worker.bgw_main_arg = UInt32GetDatum(dsm_segment_handle(pcxt->seg));
527 worker.bgw_notify_pid = MyProcPid;
528
529 /*
530 * Start workers.
531 *
532 * The caller must be able to tolerate ending up with fewer workers than
533 * expected, so there is no need to throw an error here if registration
534 * fails. It wouldn't help much anyway, because registering the worker in
535 * no way guarantees that it will start up and initialize successfully.
536 */
537 for (i = 0; i < pcxt->nworkers; ++i)
538 {
539 memcpy(worker.bgw_extra, &i, sizeof(int));
540 if (!any_registrations_failed &&
541 RegisterDynamicBackgroundWorker(&worker,
542 &pcxt->worker[i].bgwhandle))
543 {
544 shm_mq_set_handle(pcxt->worker[i].error_mqh,
545 pcxt->worker[i].bgwhandle);
546 pcxt->nworkers_launched++;
547 }
548 else
549 {
550 /*
551 * If we weren't able to register the worker, then we've bumped up
552 * against the max_worker_processes limit, and future
553 * registrations will probably fail too, so arrange to skip them.
554 * But we still have to execute this code for the remaining slots
555 * to make sure that we forget about the error queues we budgeted
556 * for those workers. Otherwise, we'll wait for them to start,
557 * but they never will.
558 */
559 any_registrations_failed = true;
560 pcxt->worker[i].bgwhandle = NULL;
561 shm_mq_detach(pcxt->worker[i].error_mqh);
562 pcxt->worker[i].error_mqh = NULL;
563 }
564 }
565
566 /*
567 * Now that nworkers_launched has taken its final value, we can initialize
568 * known_attached_workers.
569 */
570 if (pcxt->nworkers_launched > 0)
571 {
572 pcxt->known_attached_workers =
573 palloc0(sizeof(bool) * pcxt->nworkers_launched);
574 pcxt->nknown_attached_workers = 0;
575 }
576
577 /* Restore previous memory context. */
578 MemoryContextSwitchTo(oldcontext);
579}
580
581/*
582 * Wait for all workers to attach to their error queues, and throw an error if
583 * any worker fails to do this.
584 *
585 * Callers can assume that if this function returns successfully, then the
586 * number of workers given by pcxt->nworkers_launched have initialized and
587 * attached to their error queues. Whether or not these workers are guaranteed
588 * to still be running depends on what code the caller asked them to run;
589 * this function does not guarantee that they have not exited. However, it
590 * does guarantee that any workers which exited must have done so cleanly and
591 * after successfully performing the work with which they were tasked.
592 *
593 * If this function is not called, then some of the workers that were launched
594 * may not have been started due to a fork() failure, or may have exited during
595 * early startup prior to attaching to the error queue, so nworkers_launched
596 * cannot be viewed as completely reliable. It will never be less than the
597 * number of workers which actually started, but it might be more. Any workers
598 * that failed to start will still be discovered by
599 * WaitForParallelWorkersToFinish and an error will be thrown at that time,
600 * provided that function is eventually reached.
601 *
602 * In general, the leader process should do as much work as possible before
603 * calling this function. fork() failures and other early-startup failures
604 * are very uncommon, and having the leader sit idle when it could be doing
605 * useful work is undesirable. However, if the leader needs to wait for
606 * all of its workers or for a specific worker, it may want to call this
607 * function before doing so. If not, it must make some other provision for
608 * the failure-to-start case, lest it wait forever. On the other hand, a
609 * leader which never waits for a worker that might not be started yet, or
610 * at least never does so prior to WaitForParallelWorkersToFinish(), need not
611 * call this function at all.
612 */
613void
614WaitForParallelWorkersToAttach(ParallelContext *pcxt)
615{
616 int i;
617
618 /* Skip this if we have no launched workers. */
619 if (pcxt->nworkers_launched == 0)
620 return;
621
622 for (;;)
623 {
624 /*
625 * This will process any parallel messages that are pending and it may
626 * also throw an error propagated from a worker.
627 */
628 CHECK_FOR_INTERRUPTS();
629
630 for (i = 0; i < pcxt->nworkers_launched; ++i)
631 {
632 BgwHandleStatus status;
633 shm_mq *mq;
634 int rc;
635 pid_t pid;
636
637 if (pcxt->known_attached_workers[i])
638 continue;
639
640 /*
641 * If error_mqh is NULL, then the worker has already exited
642 * cleanly.
643 */
644 if (pcxt->worker[i].error_mqh == NULL)
645 {
646 pcxt->known_attached_workers[i] = true;
647 ++pcxt->nknown_attached_workers;
648 continue;
649 }
650
651 status = GetBackgroundWorkerPid(pcxt->worker[i].bgwhandle, &pid);
652 if (status == BGWH_STARTED)
653 {
654 /* Has the worker attached to the error queue? */
655 mq = shm_mq_get_queue(pcxt->worker[i].error_mqh);
656 if (shm_mq_get_sender(mq) != NULL)
657 {
658 /* Yes, so it is known to be attached. */
659 pcxt->known_attached_workers[i] = true;
660 ++pcxt->nknown_attached_workers;
661 }
662 }
663 else if (status == BGWH_STOPPED)
664 {
665 /*
666 * If the worker stopped without attaching to the error queue,
667 * throw an error.
668 */
669 mq = shm_mq_get_queue(pcxt->worker[i].error_mqh);
670 if (shm_mq_get_sender(mq) == NULL)
671 ereport(ERROR,
672 (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
673 errmsg("parallel worker failed to initialize"),
674 errhint("More details may be available in the server log.")));
675
676 pcxt->known_attached_workers[i] = true;
677 ++pcxt->nknown_attached_workers;
678 }
679 else
680 {
681 /*
682 * Worker not yet started, so we must wait. The postmaster
683 * will notify us if the worker's state changes. Our latch
684 * might also get set for some other reason, but if so we'll
685 * just end up waiting for the same worker again.
686 */
687 rc = WaitLatch(MyLatch,
688 WL_LATCH_SET | WL_EXIT_ON_PM_DEATH,
689 -1, WAIT_EVENT_BGWORKER_STARTUP);
690
691 if (rc & WL_LATCH_SET)
692 ResetLatch(MyLatch);
693 }
694 }
695
696 /* If all workers are known to have started, we're done. */
697 if (pcxt->nknown_attached_workers >= pcxt->nworkers_launched)
698 {
699 Assert(pcxt->nknown_attached_workers == pcxt->nworkers_launched);
700 break;
701 }
702 }
703}
704
705/*
706 * Wait for all workers to finish computing.
707 *
708 * Even if the parallel operation seems to have completed successfully, it's
709 * important to call this function afterwards. We must not miss any errors
710 * the workers may have thrown during the parallel operation, or any that they
711 * may yet throw while shutting down.
712 *
713 * Also, we want to update our notion of XactLastRecEnd based on worker
714 * feedback.
715 */
716void
717WaitForParallelWorkersToFinish(ParallelContext *pcxt)
718{
719 for (;;)
720 {
721 bool anyone_alive = false;
722 int nfinished = 0;
723 int i;
724
725 /*
726 * This will process any parallel messages that are pending, which may
727 * change the outcome of the loop that follows. It may also throw an
728 * error propagated from a worker.
729 */
730 CHECK_FOR_INTERRUPTS();
731
732 for (i = 0; i < pcxt->nworkers_launched; ++i)
733 {
734 /*
735 * If error_mqh is NULL, then the worker has already exited
736 * cleanly. If we have received a message through error_mqh from
737 * the worker, we know it started up cleanly, and therefore we're
738 * certain to be notified when it exits.
739 */
740 if (pcxt->worker[i].error_mqh == NULL)
741 ++nfinished;
742 else if (pcxt->known_attached_workers[i])
743 {
744 anyone_alive = true;
745 break;
746 }
747 }
748
749 if (!anyone_alive)
750 {
751 /* If all workers are known to have finished, we're done. */
752 if (nfinished >= pcxt->nworkers_launched)
753 {
754 Assert(nfinished == pcxt->nworkers_launched);
755 break;
756 }
757
758 /*
759 * We didn't detect any living workers, but not all workers are
760 * known to have exited cleanly. Either not all workers have
761 * launched yet, or maybe some of them failed to start or
762 * terminated abnormally.
763 */
764 for (i = 0; i < pcxt->nworkers_launched; ++i)
765 {
766 pid_t pid;
767 shm_mq *mq;
768
769 /*
770 * If the worker is BGWH_NOT_YET_STARTED or BGWH_STARTED, we
771 * should just keep waiting. If it is BGWH_STOPPED, then
772 * further investigation is needed.
773 */
774 if (pcxt->worker[i].error_mqh == NULL ||
775 pcxt->worker[i].bgwhandle == NULL ||
776 GetBackgroundWorkerPid(pcxt->worker[i].bgwhandle,
777 &pid) != BGWH_STOPPED)
778 continue;
779
780 /*
781 * Check whether the worker ended up stopped without ever
782 * attaching to the error queue. If so, the postmaster was
783 * unable to fork the worker or it exited without initializing
784 * properly. We must throw an error, since the caller may
785 * have been expecting the worker to do some work before
786 * exiting.
787 */
788 mq = shm_mq_get_queue(pcxt->worker[i].error_mqh);
789 if (shm_mq_get_sender(mq) == NULL)
790 ereport(ERROR,
791 (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
792 errmsg("parallel worker failed to initialize"),
793 errhint("More details may be available in the server log.")));
794
795 /*
796 * The worker is stopped, but is attached to the error queue.
797 * Unless there's a bug somewhere, this will only happen when
798 * the worker writes messages and terminates after the
799 * CHECK_FOR_INTERRUPTS() near the top of this function and
800 * before the call to GetBackgroundWorkerPid(). In that case,
801 * or latch should have been set as well and the right things
802 * will happen on the next pass through the loop.
803 */
804 }
805 }
806
807 (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, -1,
808 WAIT_EVENT_PARALLEL_FINISH);
809 ResetLatch(MyLatch);
810 }
811
812 if (pcxt->toc != NULL)
813 {
814 FixedParallelState *fps;
815
816 fps = shm_toc_lookup(pcxt->toc, PARALLEL_KEY_FIXED, false);
817 if (fps->last_xlog_end > XactLastRecEnd)
818 XactLastRecEnd = fps->last_xlog_end;
819 }
820}
821
822/*
823 * Wait for all workers to exit.
824 *
825 * This function ensures that workers have been completely shutdown. The
826 * difference between WaitForParallelWorkersToFinish and this function is
827 * that former just ensures that last message sent by worker backend is
828 * received by master backend whereas this ensures the complete shutdown.
829 */
830static void
831WaitForParallelWorkersToExit(ParallelContext *pcxt)
832{
833 int i;
834
835 /* Wait until the workers actually die. */
836 for (i = 0; i < pcxt->nworkers_launched; ++i)
837 {
838 BgwHandleStatus status;
839
840 if (pcxt->worker == NULL || pcxt->worker[i].bgwhandle == NULL)
841 continue;
842
843 status = WaitForBackgroundWorkerShutdown(pcxt->worker[i].bgwhandle);
844
845 /*
846 * If the postmaster kicked the bucket, we have no chance of cleaning
847 * up safely -- we won't be able to tell when our workers are actually
848 * dead. This doesn't necessitate a PANIC since they will all abort
849 * eventually, but we can't safely continue this session.
850 */
851 if (status == BGWH_POSTMASTER_DIED)
852 ereport(FATAL,
853 (errcode(ERRCODE_ADMIN_SHUTDOWN),
854 errmsg("postmaster exited during a parallel transaction")));
855
856 /* Release memory. */
857 pfree(pcxt->worker[i].bgwhandle);
858 pcxt->worker[i].bgwhandle = NULL;
859 }
860}
861
862/*
863 * Destroy a parallel context.
864 *
865 * If expecting a clean exit, you should use WaitForParallelWorkersToFinish()
866 * first, before calling this function. When this function is invoked, any
867 * remaining workers are forcibly killed; the dynamic shared memory segment
868 * is unmapped; and we then wait (uninterruptibly) for the workers to exit.
869 */
870void
871DestroyParallelContext(ParallelContext *pcxt)
872{
873 int i;
874
875 /*
876 * Be careful about order of operations here! We remove the parallel
877 * context from the list before we do anything else; otherwise, if an
878 * error occurs during a subsequent step, we might try to nuke it again
879 * from AtEOXact_Parallel or AtEOSubXact_Parallel.
880 */
881 dlist_delete(&pcxt->node);
882
883 /* Kill each worker in turn, and forget their error queues. */
884 if (pcxt->worker != NULL)
885 {
886 for (i = 0; i < pcxt->nworkers_launched; ++i)
887 {
888 if (pcxt->worker[i].error_mqh != NULL)
889 {
890 TerminateBackgroundWorker(pcxt->worker[i].bgwhandle);
891
892 shm_mq_detach(pcxt->worker[i].error_mqh);
893 pcxt->worker[i].error_mqh = NULL;
894 }
895 }
896 }
897
898 /*
899 * If we have allocated a shared memory segment, detach it. This will
900 * implicitly detach the error queues, and any other shared memory queues,
901 * stored there.
902 */
903 if (pcxt->seg != NULL)
904 {
905 dsm_detach(pcxt->seg);
906 pcxt->seg = NULL;
907 }
908
909 /*
910 * If this parallel context is actually in backend-private memory rather
911 * than shared memory, free that memory instead.
912 */
913 if (pcxt->private_memory != NULL)
914 {
915 pfree(pcxt->private_memory);
916 pcxt->private_memory = NULL;
917 }
918
919 /*
920 * We can't finish transaction commit or abort until all of the workers
921 * have exited. This means, in particular, that we can't respond to
922 * interrupts at this stage.
923 */
924 HOLD_INTERRUPTS();
925 WaitForParallelWorkersToExit(pcxt);
926 RESUME_INTERRUPTS();
927
928 /* Free the worker array itself. */
929 if (pcxt->worker != NULL)
930 {
931 pfree(pcxt->worker);
932 pcxt->worker = NULL;
933 }
934
935 /* Free memory. */
936 pfree(pcxt->library_name);
937 pfree(pcxt->function_name);
938 pfree(pcxt);
939}
940
941/*
942 * Are there any parallel contexts currently active?
943 */
944bool
945ParallelContextActive(void)
946{
947 return !dlist_is_empty(&pcxt_list);
948}
949
950/*
951 * Handle receipt of an interrupt indicating a parallel worker message.
952 *
953 * Note: this is called within a signal handler! All we can do is set
954 * a flag that will cause the next CHECK_FOR_INTERRUPTS() to invoke
955 * HandleParallelMessages().
956 */
957void
958HandleParallelMessageInterrupt(void)
959{
960 InterruptPending = true;
961 ParallelMessagePending = true;
962 SetLatch(MyLatch);
963}
964
965/*
966 * Handle any queued protocol messages received from parallel workers.
967 */
968void
969HandleParallelMessages(void)
970{
971 dlist_iter iter;
972 MemoryContext oldcontext;
973
974 static MemoryContext hpm_context = NULL;
975
976 /*
977 * This is invoked from ProcessInterrupts(), and since some of the
978 * functions it calls contain CHECK_FOR_INTERRUPTS(), there is a potential
979 * for recursive calls if more signals are received while this runs. It's
980 * unclear that recursive entry would be safe, and it doesn't seem useful
981 * even if it is safe, so let's block interrupts until done.
982 */
983 HOLD_INTERRUPTS();
984
985 /*
986 * Moreover, CurrentMemoryContext might be pointing almost anywhere. We
987 * don't want to risk leaking data into long-lived contexts, so let's do
988 * our work here in a private context that we can reset on each use.
989 */
990 if (hpm_context == NULL) /* first time through? */
991 hpm_context = AllocSetContextCreate(TopMemoryContext,
992 "HandleParallelMessages",
993 ALLOCSET_DEFAULT_SIZES);
994 else
995 MemoryContextReset(hpm_context);
996
997 oldcontext = MemoryContextSwitchTo(hpm_context);
998
999 /* OK to process messages. Reset the flag saying there are more to do. */
1000 ParallelMessagePending = false;
1001
1002 dlist_foreach(iter, &pcxt_list)
1003 {
1004 ParallelContext *pcxt;
1005 int i;
1006
1007 pcxt = dlist_container(ParallelContext, node, iter.cur);
1008 if (pcxt->worker == NULL)
1009 continue;
1010
1011 for (i = 0; i < pcxt->nworkers_launched; ++i)
1012 {
1013 /*
1014 * Read as many messages as we can from each worker, but stop when
1015 * either (1) the worker's error queue goes away, which can happen
1016 * if we receive a Terminate message from the worker; or (2) no
1017 * more messages can be read from the worker without blocking.
1018 */
1019 while (pcxt->worker[i].error_mqh != NULL)
1020 {
1021 shm_mq_result res;
1022 Size nbytes;
1023 void *data;
1024
1025 res = shm_mq_receive(pcxt->worker[i].error_mqh, &nbytes,
1026 &data, true);
1027 if (res == SHM_MQ_WOULD_BLOCK)
1028 break;
1029 else if (res == SHM_MQ_SUCCESS)
1030 {
1031 StringInfoData msg;
1032
1033 initStringInfo(&msg);
1034 appendBinaryStringInfo(&msg, data, nbytes);
1035 HandleParallelMessage(pcxt, i, &msg);
1036 pfree(msg.data);
1037 }
1038 else
1039 ereport(ERROR,
1040 (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
1041 errmsg("lost connection to parallel worker")));
1042 }
1043 }
1044 }
1045
1046 MemoryContextSwitchTo(oldcontext);
1047
1048 /* Might as well clear the context on our way out */
1049 MemoryContextReset(hpm_context);
1050
1051 RESUME_INTERRUPTS();
1052}
1053
1054/*
1055 * Handle a single protocol message received from a single parallel worker.
1056 */
1057static void
1058HandleParallelMessage(ParallelContext *pcxt, int i, StringInfo msg)
1059{
1060 char msgtype;
1061
1062 if (pcxt->known_attached_workers != NULL &&
1063 !pcxt->known_attached_workers[i])
1064 {
1065 pcxt->known_attached_workers[i] = true;
1066 pcxt->nknown_attached_workers++;
1067 }
1068
1069 msgtype = pq_getmsgbyte(msg);
1070
1071 switch (msgtype)
1072 {
1073 case 'K': /* BackendKeyData */
1074 {
1075 int32 pid = pq_getmsgint(msg, 4);
1076
1077 (void) pq_getmsgint(msg, 4); /* discard cancel key */
1078 (void) pq_getmsgend(msg);
1079 pcxt->worker[i].pid = pid;
1080 break;
1081 }
1082
1083 case 'E': /* ErrorResponse */
1084 case 'N': /* NoticeResponse */
1085 {
1086 ErrorData edata;
1087 ErrorContextCallback *save_error_context_stack;
1088
1089 /* Parse ErrorResponse or NoticeResponse. */
1090 pq_parse_errornotice(msg, &edata);
1091
1092 /* Death of a worker isn't enough justification for suicide. */
1093 edata.elevel = Min(edata.elevel, ERROR);
1094
1095 /*
1096 * If desired, add a context line to show that this is a
1097 * message propagated from a parallel worker. Otherwise, it
1098 * can sometimes be confusing to understand what actually
1099 * happened. (We don't do this in FORCE_PARALLEL_REGRESS mode
1100 * because it causes test-result instability depending on
1101 * whether a parallel worker is actually used or not.)
1102 */
1103 if (force_parallel_mode != FORCE_PARALLEL_REGRESS)
1104 {
1105 if (edata.context)
1106 edata.context = psprintf("%s\n%s", edata.context,
1107 _("parallel worker"));
1108 else
1109 edata.context = pstrdup(_("parallel worker"));
1110 }
1111
1112 /*
1113 * Context beyond that should use the error context callbacks
1114 * that were in effect when the ParallelContext was created,
1115 * not the current ones.
1116 */
1117 save_error_context_stack = error_context_stack;
1118 error_context_stack = pcxt->error_context_stack;
1119
1120 /* Rethrow error or print notice. */
1121 ThrowErrorData(&edata);
1122
1123 /* Not an error, so restore previous context stack. */
1124 error_context_stack = save_error_context_stack;
1125
1126 break;
1127 }
1128
1129 case 'A': /* NotifyResponse */
1130 {
1131 /* Propagate NotifyResponse. */
1132 int32 pid;
1133 const char *channel;
1134 const char *payload;
1135
1136 pid = pq_getmsgint(msg, 4);
1137 channel = pq_getmsgrawstring(msg);
1138 payload = pq_getmsgrawstring(msg);
1139 pq_endmessage(msg);
1140
1141 NotifyMyFrontEnd(channel, payload, pid);
1142
1143 break;
1144 }
1145
1146 case 'X': /* Terminate, indicating clean exit */
1147 {
1148 shm_mq_detach(pcxt->worker[i].error_mqh);
1149 pcxt->worker[i].error_mqh = NULL;
1150 break;
1151 }
1152
1153 default:
1154 {
1155 elog(ERROR, "unrecognized message type received from parallel worker: %c (message length %d bytes)",
1156 msgtype, msg->len);
1157 }
1158 }
1159}
1160
1161/*
1162 * End-of-subtransaction cleanup for parallel contexts.
1163 *
1164 * Currently, it's forbidden to enter or leave a subtransaction while
1165 * parallel mode is in effect, so we could just blow away everything. But
1166 * we may want to relax that restriction in the future, so this code
1167 * contemplates that there may be multiple subtransaction IDs in pcxt_list.
1168 */
1169void
1170AtEOSubXact_Parallel(bool isCommit, SubTransactionId mySubId)
1171{
1172 while (!dlist_is_empty(&pcxt_list))
1173 {
1174 ParallelContext *pcxt;
1175
1176 pcxt = dlist_head_element(ParallelContext, node, &pcxt_list);
1177 if (pcxt->subid != mySubId)
1178 break;
1179 if (isCommit)
1180 elog(WARNING, "leaked parallel context");
1181 DestroyParallelContext(pcxt);
1182 }
1183}
1184
1185/*
1186 * End-of-transaction cleanup for parallel contexts.
1187 */
1188void
1189AtEOXact_Parallel(bool isCommit)
1190{
1191 while (!dlist_is_empty(&pcxt_list))
1192 {
1193 ParallelContext *pcxt;
1194
1195 pcxt = dlist_head_element(ParallelContext, node, &pcxt_list);
1196 if (isCommit)
1197 elog(WARNING, "leaked parallel context");
1198 DestroyParallelContext(pcxt);
1199 }
1200}
1201
1202/*
1203 * Main entrypoint for parallel workers.
1204 */
1205void
1206ParallelWorkerMain(Datum main_arg)
1207{
1208 dsm_segment *seg;
1209 shm_toc *toc;
1210 FixedParallelState *fps;
1211 char *error_queue_space;
1212 shm_mq *mq;
1213 shm_mq_handle *mqh;
1214 char *libraryspace;
1215 char *entrypointstate;
1216 char *library_name;
1217 char *function_name;
1218 parallel_worker_main_type entrypt;
1219 char *gucspace;
1220 char *combocidspace;
1221 char *tsnapspace;
1222 char *asnapspace;
1223 char *tstatespace;
1224 char *reindexspace;
1225 char *relmapperspace;
1226 char *enumblacklistspace;
1227 StringInfoData msgbuf;
1228 char *session_dsm_handle_space;
1229
1230 /* Set flag to indicate that we're initializing a parallel worker. */
1231 InitializingParallelWorker = true;
1232
1233 /* Establish signal handlers. */
1234 pqsignal(SIGTERM, die);
1235 BackgroundWorkerUnblockSignals();
1236
1237 /* Determine and set our parallel worker number. */
1238 Assert(ParallelWorkerNumber == -1);
1239 memcpy(&ParallelWorkerNumber, MyBgworkerEntry->bgw_extra, sizeof(int));
1240
1241 /* Set up a memory context to work in, just for cleanliness. */
1242 CurrentMemoryContext = AllocSetContextCreate(TopMemoryContext,
1243 "Parallel worker",
1244 ALLOCSET_DEFAULT_SIZES);
1245
1246 /*
1247 * Attach to the dynamic shared memory segment for the parallel query, and
1248 * find its table of contents.
1249 *
1250 * Note: at this point, we have not created any ResourceOwner in this
1251 * process. This will result in our DSM mapping surviving until process
1252 * exit, which is fine. If there were a ResourceOwner, it would acquire
1253 * ownership of the mapping, but we have no need for that.
1254 */
1255 seg = dsm_attach(DatumGetUInt32(main_arg));
1256 if (seg == NULL)
1257 ereport(ERROR,
1258 (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
1259 errmsg("could not map dynamic shared memory segment")));
1260 toc = shm_toc_attach(PARALLEL_MAGIC, dsm_segment_address(seg));
1261 if (toc == NULL)
1262 ereport(ERROR,
1263 (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
1264 errmsg("invalid magic number in dynamic shared memory segment")));
1265
1266 /* Look up fixed parallel state. */
1267 fps = shm_toc_lookup(toc, PARALLEL_KEY_FIXED, false);
1268 MyFixedParallelState = fps;
1269
1270 /* Arrange to signal the leader if we exit. */
1271 ParallelMasterPid = fps->parallel_master_pid;
1272 ParallelMasterBackendId = fps->parallel_master_backend_id;
1273 on_shmem_exit(ParallelWorkerShutdown, (Datum) 0);
1274
1275 /*
1276 * Now we can find and attach to the error queue provided for us. That's
1277 * good, because until we do that, any errors that happen here will not be
1278 * reported back to the process that requested that this worker be
1279 * launched.
1280 */
1281 error_queue_space = shm_toc_lookup(toc, PARALLEL_KEY_ERROR_QUEUE, false);
1282 mq = (shm_mq *) (error_queue_space +
1283 ParallelWorkerNumber * PARALLEL_ERROR_QUEUE_SIZE);
1284 shm_mq_set_sender(mq, MyProc);
1285 mqh = shm_mq_attach(mq, seg, NULL);
1286 pq_redirect_to_shm_mq(seg, mqh);
1287 pq_set_parallel_master(fps->parallel_master_pid,
1288 fps->parallel_master_backend_id);
1289
1290 /*
1291 * Send a BackendKeyData message to the process that initiated parallelism
1292 * so that it has access to our PID before it receives any other messages
1293 * from us. Our cancel key is sent, too, since that's the way the
1294 * protocol message is defined, but it won't actually be used for anything
1295 * in this case.
1296 */
1297 pq_beginmessage(&msgbuf, 'K');
1298 pq_sendint32(&msgbuf, (int32) MyProcPid);
1299 pq_sendint32(&msgbuf, (int32) MyCancelKey);
1300 pq_endmessage(&msgbuf);
1301
1302 /*
1303 * Hooray! Primary initialization is complete. Now, we need to set up our
1304 * backend-local state to match the original backend.
1305 */
1306
1307 /*
1308 * Join locking group. We must do this before anything that could try to
1309 * acquire a heavyweight lock, because any heavyweight locks acquired to
1310 * this point could block either directly against the parallel group
1311 * leader or against some process which in turn waits for a lock that
1312 * conflicts with the parallel group leader, causing an undetected
1313 * deadlock. (If we can't join the lock group, the leader has gone away,
1314 * so just exit quietly.)
1315 */
1316 if (!BecomeLockGroupMember(fps->parallel_master_pgproc,
1317 fps->parallel_master_pid))
1318 return;
1319
1320 /*
1321 * Restore transaction and statement start-time timestamps. This must
1322 * happen before anything that would start a transaction, else asserts in
1323 * xact.c will fire.
1324 */
1325 SetParallelStartTimestamps(fps->xact_ts, fps->stmt_ts);
1326
1327 /*
1328 * Identify the entry point to be called. In theory this could result in
1329 * loading an additional library, though most likely the entry point is in
1330 * the core backend or in a library we just loaded.
1331 */
1332 entrypointstate = shm_toc_lookup(toc, PARALLEL_KEY_ENTRYPOINT, false);
1333 library_name = entrypointstate;
1334 function_name = entrypointstate + strlen(library_name) + 1;
1335
1336 entrypt = LookupParallelWorkerFunction(library_name, function_name);
1337
1338 /* Restore database connection. */
1339 BackgroundWorkerInitializeConnectionByOid(fps->database_id,
1340 fps->authenticated_user_id,
1341 0);
1342
1343 /*
1344 * Set the client encoding to the database encoding, since that is what
1345 * the leader will expect.
1346 */
1347 SetClientEncoding(GetDatabaseEncoding());
1348
1349 /*
1350 * Load libraries that were loaded by original backend. We want to do
1351 * this before restoring GUCs, because the libraries might define custom
1352 * variables.
1353 */
1354 libraryspace = shm_toc_lookup(toc, PARALLEL_KEY_LIBRARY, false);
1355 StartTransactionCommand();
1356 RestoreLibraryState(libraryspace);
1357
1358 /* Restore GUC values from launching backend. */
1359 gucspace = shm_toc_lookup(toc, PARALLEL_KEY_GUC, false);
1360 RestoreGUCState(gucspace);
1361 CommitTransactionCommand();
1362
1363 /* Crank up a transaction state appropriate to a parallel worker. */
1364 tstatespace = shm_toc_lookup(toc, PARALLEL_KEY_TRANSACTION_STATE, false);
1365 StartParallelWorkerTransaction(tstatespace);
1366
1367 /* Restore combo CID state. */
1368 combocidspace = shm_toc_lookup(toc, PARALLEL_KEY_COMBO_CID, false);
1369 RestoreComboCIDState(combocidspace);
1370
1371 /* Attach to the per-session DSM segment and contained objects. */
1372 session_dsm_handle_space =
1373 shm_toc_lookup(toc, PARALLEL_KEY_SESSION_DSM, false);
1374 AttachSession(*(dsm_handle *) session_dsm_handle_space);
1375
1376 /* Restore transaction snapshot. */
1377 tsnapspace = shm_toc_lookup(toc, PARALLEL_KEY_TRANSACTION_SNAPSHOT, false);
1378 RestoreTransactionSnapshot(RestoreSnapshot(tsnapspace),
1379 fps->parallel_master_pgproc);
1380
1381 /* Restore active snapshot. */
1382 asnapspace = shm_toc_lookup(toc, PARALLEL_KEY_ACTIVE_SNAPSHOT, false);
1383 PushActiveSnapshot(RestoreSnapshot(asnapspace));
1384
1385 /*
1386 * We've changed which tuples we can see, and must therefore invalidate
1387 * system caches.
1388 */
1389 InvalidateSystemCaches();
1390
1391 /*
1392 * Restore current role id. Skip verifying whether session user is
1393 * allowed to become this role and blindly restore the leader's state for
1394 * current role.
1395 */
1396 SetCurrentRoleId(fps->outer_user_id, fps->is_superuser);
1397
1398 /* Restore user ID and security context. */
1399 SetUserIdAndSecContext(fps->current_user_id, fps->sec_context);
1400
1401 /* Restore temp-namespace state to ensure search path matches leader's. */
1402 SetTempNamespaceState(fps->temp_namespace_id,
1403 fps->temp_toast_namespace_id);
1404
1405 /* Restore reindex state. */
1406 reindexspace = shm_toc_lookup(toc, PARALLEL_KEY_REINDEX_STATE, false);
1407 RestoreReindexState(reindexspace);
1408
1409 /* Restore relmapper state. */
1410 relmapperspace = shm_toc_lookup(toc, PARALLEL_KEY_RELMAPPER_STATE, false);
1411 RestoreRelationMap(relmapperspace);
1412
1413 /* Restore enum blacklist. */
1414 enumblacklistspace = shm_toc_lookup(toc, PARALLEL_KEY_ENUMBLACKLIST,
1415 false);
1416 RestoreEnumBlacklist(enumblacklistspace);
1417
1418 /* Attach to the leader's serializable transaction, if SERIALIZABLE. */
1419 AttachSerializableXact(fps->serializable_xact_handle);
1420
1421 /*
1422 * We've initialized all of our state now; nothing should change
1423 * hereafter.
1424 */
1425 InitializingParallelWorker = false;
1426 EnterParallelMode();
1427
1428 /*
1429 * Time to do the real work: invoke the caller-supplied code.
1430 */
1431 entrypt(seg, toc);
1432
1433 /* Must exit parallel mode to pop active snapshot. */
1434 ExitParallelMode();
1435
1436 /* Must pop active snapshot so snapmgr.c doesn't complain. */
1437 PopActiveSnapshot();
1438
1439 /* Shut down the parallel-worker transaction. */
1440 EndParallelWorkerTransaction();
1441
1442 /* Detach from the per-session DSM segment. */
1443 DetachSession();
1444
1445 /* Report success. */
1446 pq_putmessage('X', NULL, 0);
1447}
1448
1449/*
1450 * Update shared memory with the ending location of the last WAL record we
1451 * wrote, if it's greater than the value already stored there.
1452 */
1453void
1454ParallelWorkerReportLastRecEnd(XLogRecPtr last_xlog_end)
1455{
1456 FixedParallelState *fps = MyFixedParallelState;
1457
1458 Assert(fps != NULL);
1459 SpinLockAcquire(&fps->mutex);
1460 if (fps->last_xlog_end < last_xlog_end)
1461 fps->last_xlog_end = last_xlog_end;
1462 SpinLockRelease(&fps->mutex);
1463}
1464
1465/*
1466 * Make sure the leader tries to read from our error queue one more time.
1467 * This guards against the case where we exit uncleanly without sending an
1468 * ErrorResponse to the leader, for example because some code calls proc_exit
1469 * directly.
1470 */
1471static void
1472ParallelWorkerShutdown(int code, Datum arg)
1473{
1474 SendProcSignal(ParallelMasterPid,
1475 PROCSIG_PARALLEL_MESSAGE,
1476 ParallelMasterBackendId);
1477}
1478
1479/*
1480 * Look up (and possibly load) a parallel worker entry point function.
1481 *
1482 * For functions contained in the core code, we use library name "postgres"
1483 * and consult the InternalParallelWorkers array. External functions are
1484 * looked up, and loaded if necessary, using load_external_function().
1485 *
1486 * The point of this is to pass function names as strings across process
1487 * boundaries. We can't pass actual function addresses because of the
1488 * possibility that the function has been loaded at a different address
1489 * in a different process. This is obviously a hazard for functions in
1490 * loadable libraries, but it can happen even for functions in the core code
1491 * on platforms using EXEC_BACKEND (e.g., Windows).
1492 *
1493 * At some point it might be worthwhile to get rid of InternalParallelWorkers[]
1494 * in favor of applying load_external_function() for core functions too;
1495 * but that raises portability issues that are not worth addressing now.
1496 */
1497static parallel_worker_main_type
1498LookupParallelWorkerFunction(const char *libraryname, const char *funcname)
1499{
1500 /*
1501 * If the function is to be loaded from postgres itself, search the
1502 * InternalParallelWorkers array.
1503 */
1504 if (strcmp(libraryname, "postgres") == 0)
1505 {
1506 int i;
1507
1508 for (i = 0; i < lengthof(InternalParallelWorkers); i++)
1509 {
1510 if (strcmp(InternalParallelWorkers[i].fn_name, funcname) == 0)
1511 return InternalParallelWorkers[i].fn_addr;
1512 }
1513
1514 /* We can only reach this by programming error. */
1515 elog(ERROR, "internal function \"%s\" not found", funcname);
1516 }
1517
1518 /* Otherwise load from external library. */
1519 return (parallel_worker_main_type)
1520 load_external_function(libraryname, funcname, true, NULL);
1521}
1522