1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
|
/**
* Copyright (C) 2015 MongoDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the GNU Affero General Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#define MONGO_LOG_DEFAULT_COMPONENT ::mongo::logger::LogComponent::kQuery
#include "mongo/platform/basic.h"
#include <memory>
#include <string>
#include "mongo/base/disallow_copying.h"
#include "mongo/db/auth/authorization_session.h"
#include "mongo/db/catalog/collection.h"
#include "mongo/db/client.h"
#include "mongo/db/clientcursor.h"
#include "mongo/db/commands.h"
#include "mongo/db/curop.h"
#include "mongo/db/curop_failpoint_helpers.h"
#include "mongo/db/cursor_manager.h"
#include "mongo/db/db_raii.h"
#include "mongo/db/exec/working_set_common.h"
#include "mongo/db/query/cursor_response.h"
#include "mongo/db/query/find.h"
#include "mongo/db/query/find_common.h"
#include "mongo/db/query/getmore_request.h"
#include "mongo/db/query/plan_executor.h"
#include "mongo/db/query/plan_summary_stats.h"
#include "mongo/db/repl/oplog.h"
#include "mongo/db/repl/replication_coordinator.h"
#include "mongo/db/service_context.h"
#include "mongo/db/stats/counters.h"
#include "mongo/db/stats/top.h"
#include "mongo/s/chunk_version.h"
#include "mongo/stdx/memory.h"
#include "mongo/util/fail_point_service.h"
#include "mongo/util/log.h"
#include "mongo/util/scopeguard.h"
#include "mongo/util/time_support.h"
namespace mongo {
namespace {
MONGO_FAIL_POINT_DEFINE(rsStopGetMoreCmd);
MONGO_FAIL_POINT_DEFINE(waitWithPinnedCursorDuringGetMoreBatch);
/**
* Validates that the lsid of 'opCtx' matches that of 'cursor'. This must be called after
* authenticating, so that it is safe to report the lsid of 'cursor'.
*/
void validateLSID(OperationContext* opCtx, const GetMoreRequest& request, ClientCursor* cursor) {
uassert(50736,
str::stream() << "Cannot run getMore on cursor " << request.cursorid
<< ", which was not created in a session, in session "
<< *opCtx->getLogicalSessionId(),
!opCtx->getLogicalSessionId() || cursor->getSessionId());
uassert(50737,
str::stream() << "Cannot run getMore on cursor " << request.cursorid
<< ", which was created in session "
<< *cursor->getSessionId()
<< ", without an lsid",
opCtx->getLogicalSessionId() || !cursor->getSessionId());
uassert(50738,
str::stream() << "Cannot run getMore on cursor " << request.cursorid
<< ", which was created in session "
<< *cursor->getSessionId()
<< ", in session "
<< *opCtx->getLogicalSessionId(),
!opCtx->getLogicalSessionId() || !cursor->getSessionId() ||
(*opCtx->getLogicalSessionId() == *cursor->getSessionId()));
}
/**
* Validates that the txnNumber of 'opCtx' matches that of 'cursor'. This must be called after
* authenticating, so that it is safe to report the txnNumber of 'cursor'.
*/
void validateTxnNumber(OperationContext* opCtx,
const GetMoreRequest& request,
ClientCursor* cursor) {
uassert(50739,
str::stream() << "Cannot run getMore on cursor " << request.cursorid
<< ", which was not created in a transaction, in transaction "
<< *opCtx->getTxnNumber(),
!opCtx->getTxnNumber() || cursor->getTxnNumber());
uassert(50740,
str::stream() << "Cannot run getMore on cursor " << request.cursorid
<< ", which was created in transaction "
<< *cursor->getTxnNumber()
<< ", without a txnNumber",
opCtx->getTxnNumber() || !cursor->getTxnNumber());
uassert(50741,
str::stream() << "Cannot run getMore on cursor " << request.cursorid
<< ", which was created in transaction "
<< *cursor->getTxnNumber()
<< ", in transaction "
<< *opCtx->getTxnNumber(),
!opCtx->getTxnNumber() || !cursor->getTxnNumber() ||
(*opCtx->getTxnNumber() == *cursor->getTxnNumber()));
}
/**
* A command for running getMore() against an existing cursor registered with a CursorManager.
* Used to generate the next batch of results for a ClientCursor.
*
* Can be used in combination with any cursor-generating command (e.g. find, aggregate,
* listIndexes).
*/
class GetMoreCmd : public BasicCommand {
MONGO_DISALLOW_COPYING(GetMoreCmd);
public:
GetMoreCmd() : BasicCommand("getMore") {}
virtual bool supportsWriteConcern(const BSONObj& cmd) const override {
return false;
}
virtual bool allowsAfterClusterTime(const BSONObj& cmdObj) const override {
return false;
}
AllowedOnSecondary secondaryAllowed(ServiceContext*) const override {
return AllowedOnSecondary::kAlways;
}
bool maintenanceOk() const override {
return false;
}
bool adminOnly() const override {
return false;
}
bool supportsReadConcern(const std::string& dbName,
const BSONObj& cmdObj,
repl::ReadConcernLevel level) const final {
// Uses the readConcern setting from whatever created the cursor.
return level == repl::ReadConcernLevel::kLocalReadConcern;
}
ReadWriteType getReadWriteType() const {
return ReadWriteType::kRead;
}
std::string help() const override {
return "retrieve more results from an existing cursor";
}
LogicalOp getLogicalOp() const override {
return LogicalOp::opGetMore;
}
std::size_t reserveBytesForReply() const override {
// The extra 1K is an artifact of how we construct batches. We consider a batch to be full
// when it exceeds the goal batch size. In the case that we are just below the limit and
// then read a large document, the extra 1K helps prevent a final realloc+memcpy.
return FindCommon::kMaxBytesToReturnToClientAtOnce + 1024u;
}
/**
* A getMore command increments the getMore counter, not the command counter.
*/
bool shouldAffectCommandCounter() const override {
return false;
}
std::string parseNs(const std::string& dbname, const BSONObj& cmdObj) const override {
return GetMoreRequest::parseNs(dbname, cmdObj).ns();
}
Status checkAuthForCommand(Client* client,
const std::string& dbname,
const BSONObj& cmdObj) const override {
StatusWith<GetMoreRequest> parseStatus = GetMoreRequest::parseFromBSON(dbname, cmdObj);
if (!parseStatus.isOK()) {
return parseStatus.getStatus();
}
const GetMoreRequest& request = parseStatus.getValue();
return AuthorizationSession::get(client)->checkAuthForGetMore(
request.nss, request.cursorid, request.term.is_initialized());
}
bool runParsed(OperationContext* opCtx,
const NamespaceString& origNss,
const GetMoreRequest& request,
const BSONObj& cmdObj,
BSONObjBuilder& result) {
auto curOp = CurOp::get(opCtx);
curOp->debug().cursorid = request.cursorid;
// Validate term before acquiring locks, if provided.
if (request.term) {
auto replCoord = repl::ReplicationCoordinator::get(opCtx);
Status status = replCoord->updateTerm(opCtx, *request.term);
// Note: updateTerm returns ok if term stayed the same.
uassertStatusOK(status);
}
// Cursors come in one of two flavors:
// - Cursors owned by the collection cursor manager, such as those generated via the find
// command. For these cursors, we hold the appropriate collection lock for the duration of
// the getMore using AutoGetCollectionForRead.
// - Cursors owned by the global cursor manager, such as those generated via the aggregate
// command. These cursors either hold no collection state or manage their collection state
// internally, so we acquire no locks.
//
// While we only need to acquire locks in the case of a cursor which is *not* globally
// owned, we need to create an AutoStatsTracker in either case. This is responsible for
// updating statistics in CurOp and Top. We avoid using AutoGetCollectionForReadCommand
// because we may need to drop and reacquire locks when the cursor is awaitData, but we
// don't want to update the stats twice.
//
// Note that we acquire our locks before our ClientCursorPin, in order to ensure that
// the pin's destructor is called before the lock's destructor (if there is one) so that the
// cursor cleanup can occur under the lock.
boost::optional<AutoGetCollectionForRead> readLock;
boost::optional<AutoStatsTracker> statsTracker;
CursorManager* cursorManager;
if (CursorManager::isGloballyManagedCursor(request.cursorid)) {
cursorManager = CursorManager::getGlobalCursorManager();
if (boost::optional<NamespaceString> nssForCurOp =
request.nss.isGloballyManagedNamespace()
? request.nss.getTargetNSForGloballyManagedNamespace()
: request.nss) {
const boost::optional<int> dbProfilingLevel = boost::none;
statsTracker.emplace(
opCtx, *nssForCurOp, Top::LockType::NotLocked, dbProfilingLevel);
}
} else {
readLock.emplace(opCtx, request.nss);
const int doNotChangeProfilingLevel = 0;
statsTracker.emplace(opCtx,
request.nss,
Top::LockType::ReadLocked,
readLock->getDb() ? readLock->getDb()->getProfilingLevel()
: doNotChangeProfilingLevel);
Collection* collection = readLock->getCollection();
if (!collection) {
uasserted(ErrorCodes::OperationFailed, "collection dropped between getMore calls");
}
cursorManager = collection->getCursorManager();
}
auto ccPin = cursorManager->pinCursor(opCtx, request.cursorid);
uassertStatusOK(ccPin.getStatus());
ClientCursor* cursor = ccPin.getValue().getCursor();
// Only used by the failpoints.
const auto dropAndReaquireReadLock = [&readLock, opCtx, &request]() {
// Make sure an interrupted operation does not prevent us from reacquiring the lock.
UninterruptibleLockGuard noInterrupt(opCtx->lockState());
readLock.reset();
readLock.emplace(opCtx, request.nss);
};
// If the 'waitAfterPinningCursorBeforeGetMoreBatch' fail point is enabled, set the 'msg'
// field of this operation's CurOp to signal that we've hit this point and then repeatedly
// release and re-acquire the collection readLock at regular intervals until the failpoint
// is released. This is done in order to avoid deadlocks caused by the pinned-cursor
// failpoints in this file (see SERVER-21997).
if (MONGO_FAIL_POINT(waitAfterPinningCursorBeforeGetMoreBatch)) {
CurOpFailpointHelpers::waitWhileFailPointEnabled(
&waitAfterPinningCursorBeforeGetMoreBatch,
opCtx,
"waitAfterPinningCursorBeforeGetMoreBatch",
dropAndReaquireReadLock);
}
// A user can only call getMore on their own cursor. If there were multiple users
// authenticated when the cursor was created, then at least one of them must be
// authenticated in order to run getMore on the cursor.
if (!AuthorizationSession::get(opCtx->getClient())
->isCoauthorizedWith(cursor->getAuthenticatedUsers())) {
uasserted(ErrorCodes::Unauthorized,
str::stream() << "cursor id " << request.cursorid
<< " was not created by the authenticated user");
}
if (request.nss != cursor->nss()) {
uasserted(ErrorCodes::Unauthorized,
str::stream() << "Requested getMore on namespace '" << request.nss.ns()
<< "', but cursor belongs to a different namespace "
<< cursor->nss().ns());
}
// Ensure the lsid and txnNumber of the getMore match that of the originating command.
validateLSID(opCtx, request, cursor);
validateTxnNumber(opCtx, request, cursor);
if (request.nss.isOplog() && MONGO_FAIL_POINT(rsStopGetMoreCmd)) {
uasserted(ErrorCodes::CommandFailed,
str::stream() << "getMore on " << request.nss.ns()
<< " rejected due to active fail point rsStopGetMoreCmd");
}
// Validation related to awaitData.
if (cursor->isAwaitData()) {
invariant(cursor->isTailable());
}
if (request.awaitDataTimeout && !cursor->isAwaitData()) {
Status status(ErrorCodes::BadValue,
"cannot set maxTimeMS on getMore command for a non-awaitData cursor");
uassertStatusOK(status);
}
// On early return, get rid of the cursor.
ScopeGuard cursorFreer = MakeGuard(&ClientCursorPin::deleteUnderlying, &ccPin.getValue());
const auto replicationMode = repl::ReplicationCoordinator::get(opCtx)->getReplicationMode();
if (replicationMode == repl::ReplicationCoordinator::modeReplSet &&
cursor->getReadConcernLevel() == repl::ReadConcernLevel::kMajorityReadConcern) {
opCtx->recoveryUnit()->setTimestampReadSource(
RecoveryUnit::ReadSource::kMajorityCommitted);
uassertStatusOK(opCtx->recoveryUnit()->obtainMajorityCommittedSnapshot());
}
const bool disableAwaitDataFailpointActive =
MONGO_FAIL_POINT(disableAwaitDataForGetMoreCmd);
// We assume that cursors created through a DBDirectClient are always used from their
// original OperationContext, so we do not need to move time to and from the cursor.
if (!opCtx->getClient()->isInDirectClient()) {
// There is no time limit set directly on this getMore command. If the cursor is
// awaitData, then we supply a default time of one second. Otherwise we roll over
// any leftover time from the maxTimeMS of the operation that spawned this cursor,
// applying it to this getMore.
if (cursor->isAwaitData() && !disableAwaitDataFailpointActive) {
awaitDataState(opCtx).waitForInsertsDeadline =
opCtx->getServiceContext()->getPreciseClockSource()->now() +
request.awaitDataTimeout.value_or(Seconds{1});
} else if (cursor->getLeftoverMaxTimeMicros() < Microseconds::max()) {
opCtx->setDeadlineAfterNowBy(cursor->getLeftoverMaxTimeMicros());
}
}
if (!cursor->isAwaitData()) {
opCtx->checkForInterrupt(); // May trigger maxTimeAlwaysTimeOut fail point.
}
PlanExecutor* exec = cursor->getExecutor();
exec->reattachToOperationContext(opCtx);
uassertStatusOK(exec->restoreState());
auto planSummary = Explain::getPlanSummary(exec);
{
stdx::lock_guard<Client> lk(*opCtx->getClient());
curOp->setPlanSummary_inlock(planSummary);
// Ensure that the original query or command object is available in the slow query log,
// profiler and currentOp.
auto originatingCommand = cursor->getOriginatingCommandObj();
if (!originatingCommand.isEmpty()) {
curOp->setOriginatingCommand_inlock(originatingCommand);
}
}
CursorId respondWithId = 0;
CursorResponseBuilder nextBatch(/*isInitialResponse*/ false, &result);
BSONObj obj;
PlanExecutor::ExecState state = PlanExecutor::ADVANCED;
long long numResults = 0;
// We report keysExamined and docsExamined to OpDebug for a given getMore operation. To
// obtain these values we need to take a diff of the pre-execution and post-execution
// metrics, as they accumulate over the course of a cursor's lifetime.
PlanSummaryStats preExecutionStats;
Explain::getSummaryStats(*exec, &preExecutionStats);
// Mark this as an AwaitData operation if appropriate.
if (cursor->isAwaitData() && !disableAwaitDataFailpointActive) {
if (request.lastKnownCommittedOpTime)
clientsLastKnownCommittedOpTime(opCtx) = request.lastKnownCommittedOpTime.get();
awaitDataState(opCtx).shouldWaitForInserts = true;
}
// We're about to begin running the PlanExecutor in order to fill the getMore batch. If the
// 'waitWithPinnedCursorDuringGetMoreBatch' failpoint is active, set the 'msg' field of this
// operation's CurOp to signal that we've hit this point and then spin until the failpoint
// is released.
if (MONGO_FAIL_POINT(waitWithPinnedCursorDuringGetMoreBatch)) {
CurOpFailpointHelpers::waitWhileFailPointEnabled(
&waitWithPinnedCursorDuringGetMoreBatch,
opCtx,
"waitWithPinnedCursorDuringGetMoreBatch",
dropAndReaquireReadLock);
}
Status batchStatus = generateBatch(opCtx, cursor, request, &nextBatch, &state, &numResults);
uassertStatusOK(batchStatus);
PlanSummaryStats postExecutionStats;
Explain::getSummaryStats(*exec, &postExecutionStats);
postExecutionStats.totalKeysExamined -= preExecutionStats.totalKeysExamined;
postExecutionStats.totalDocsExamined -= preExecutionStats.totalDocsExamined;
curOp->debug().setPlanSummaryMetrics(postExecutionStats);
// We do not report 'execStats' for aggregation or other globally managed cursors, both in
// the original request and subsequent getMore. It would be useful to have this information
// for an aggregation, but the source PlanExecutor could be destroyed before we know whether
// we need execStats and we do not want to generate for all operations due to cost.
if (!CursorManager::isGloballyManagedCursor(request.cursorid) && curOp->shouldDBProfile()) {
BSONObjBuilder execStatsBob;
Explain::getWinningPlanStats(exec, &execStatsBob);
curOp->debug().execStats = execStatsBob.obj();
}
if (shouldSaveCursorGetMore(state, exec, cursor->isTailable())) {
respondWithId = request.cursorid;
exec->saveState();
exec->detachFromOperationContext();
cursor->setLeftoverMaxTimeMicros(opCtx->getRemainingMaxTimeMicros());
cursor->incPos(numResults);
} else {
curOp->debug().cursorExhausted = true;
}
nextBatch.done(respondWithId, request.nss.ns());
// Ensure log and profiler include the number of results returned in this getMore's response
// batch.
curOp->debug().nreturned = numResults;
if (respondWithId) {
cursorFreer.Dismiss();
}
// We're about to unpin the cursor as the ClientCursorPin goes out of scope (or delete it,
// if it has been exhausted). If the 'waitBeforeUnpinningOrDeletingCursorAfterGetMoreBatch'
// failpoint is active, set the 'msg' field of this operation's CurOp to signal that we've
// hit this point and then spin until the failpoint is released.
if (MONGO_FAIL_POINT(waitBeforeUnpinningOrDeletingCursorAfterGetMoreBatch)) {
CurOpFailpointHelpers::waitWhileFailPointEnabled(
&waitBeforeUnpinningOrDeletingCursorAfterGetMoreBatch,
opCtx,
"waitBeforeUnpinningOrDeletingCursorAfterGetMoreBatch",
dropAndReaquireReadLock);
}
return true;
}
bool run(OperationContext* opCtx,
const std::string& dbname,
const BSONObj& cmdObj,
BSONObjBuilder& result) override {
// Counted as a getMore, not as a command.
globalOpCounters.gotGetMore();
StatusWith<GetMoreRequest> parsedRequest = GetMoreRequest::parseFromBSON(dbname, cmdObj);
uassertStatusOK(parsedRequest.getStatus());
auto request = parsedRequest.getValue();
return runParsed(opCtx, request.nss, request, cmdObj, result);
}
/**
* Uses 'cursor' and 'request' to fill out 'nextBatch' with the batch of result documents to
* be returned by this getMore.
*
* Returns the number of documents in the batch in *numResults, which must be initialized to
* zero by the caller. Returns the final ExecState returned by the cursor in *state.
*
* Returns an OK status if the batch was successfully generated, and a non-OK status if the
* PlanExecutor encounters a failure.
*/
Status generateBatch(OperationContext* opCtx,
ClientCursor* cursor,
const GetMoreRequest& request,
CursorResponseBuilder* nextBatch,
PlanExecutor::ExecState* state,
long long* numResults) {
PlanExecutor* exec = cursor->getExecutor();
// If an awaitData getMore is killed during this process due to our max time expiring at
// an interrupt point, we just continue as normal and return rather than reporting a
// timeout to the user.
BSONObj obj;
try {
while (!FindCommon::enoughForGetMore(request.batchSize.value_or(0), *numResults) &&
PlanExecutor::ADVANCED == (*state = exec->getNext(&obj, NULL))) {
// If adding this object will cause us to exceed the message size limit, then we
// stash it for later.
if (!FindCommon::haveSpaceForNext(obj, *numResults, nextBatch->bytesUsed())) {
exec->enqueue(obj);
break;
}
// As soon as we get a result, this operation no longer waits.
awaitDataState(opCtx).shouldWaitForInserts = false;
// Add result to output buffer.
nextBatch->setLatestOplogTimestamp(exec->getLatestOplogTimestamp());
nextBatch->append(obj);
(*numResults)++;
}
} catch (const ExceptionFor<ErrorCodes::CloseChangeStream>&) {
// FAILURE state will make getMore command close the cursor even if it's tailable.
*state = PlanExecutor::FAILURE;
return Status::OK();
}
switch (*state) {
case PlanExecutor::FAILURE:
// Log an error message and then perform the same cleanup as DEAD.
error() << "GetMore command executor error: " << PlanExecutor::statestr(*state)
<< ", stats: " << redact(Explain::getWinningPlanStats(exec));
case PlanExecutor::DEAD: {
nextBatch->abandon();
// We should always have a valid status member object at this point.
auto status = WorkingSetCommon::getMemberObjectStatus(obj);
invariant(!status.isOK());
return status;
}
case PlanExecutor::IS_EOF:
// This causes the reported latest oplog timestamp to advance even when there are
// no results for this particular query.
nextBatch->setLatestOplogTimestamp(exec->getLatestOplogTimestamp());
default:
return Status::OK();
}
MONGO_UNREACHABLE;
}
} getMoreCmd;
} // namespace
} // namespace mongo
|