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/**
* 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/catalog/cursor_manager.h"
#include "mongo/db/client.h"
#include "mongo/db/clientcursor.h"
#include "mongo/db/commands.h"
#include "mongo/db/curop.h"
#include "mongo/db/db_raii.h"
#include "mongo/db/exec/working_set_common.h"
#include "mongo/db/global_timestamp.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_summary_stats.h"
#include "mongo/db/repl/oplog.h"
#include "mongo/db/repl/replication_coordinator_global.h"
#include "mongo/db/s/operation_sharding_state.h"
#include "mongo/db/service_context.h"
#include "mongo/db/stats/counters.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_FP_DECLARE(rsStopGetMoreCmd);
} // namespace
/**
* 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 Command {
MONGO_DISALLOW_COPYING(GetMoreCmd);
public:
GetMoreCmd() : Command("getMore") {}
virtual bool supportsWriteConcern(const BSONObj& cmd) const override {
return false;
}
bool slaveOk() const override {
return true;
}
bool maintenanceOk() const override {
return false;
}
bool adminOnly() const override {
return false;
}
bool supportsReadConcern() const final {
// Uses the readConcern setting from whatever created the cursor.
return false;
}
ReadWriteType getReadWriteType() const {
return ReadWriteType::kRead;
}
void help(std::stringstream& help) const override {
help << "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) 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* txn,
const NamespaceString& origNss,
const GetMoreRequest& request,
BSONObj& cmdObj,
std::string& errmsg,
BSONObjBuilder& result) {
auto curOp = CurOp::get(txn);
curOp->debug().cursorid = request.cursorid;
// Disable shard version checking - getmore commands are always unversioned
OperationShardingState::get(txn).setShardVersion(request.nss, ChunkVersion::IGNORED());
// Validate term before acquiring locks, if provided.
if (request.term) {
auto replCoord = repl::ReplicationCoordinator::get(txn);
Status status = replCoord->updateTerm(txn, *request.term);
// Note: updateTerm returns ok if term stayed the same.
if (!status.isOK()) {
return appendCommandStatus(result, status);
}
}
// Depending on the type of cursor being operated on, we hold locks for the whole
// getMore, or none of the getMore, or part of the getMore. The three cases in detail:
//
// 1) Normal cursor: we lock with "ctx" and hold it for the whole getMore.
// 2) Cursor owned by global cursor manager: we don't lock anything. These cursors
// don't own any collection state. These cursors are generated either by the
// listCollections or listIndexes commands, as these special cursor-generating commands
// operate over catalog data rather than targeting the data within a collection.
// 3) Agg cursor: we lock with "ctx", then release, then relock with "unpinDBLock" and
// "unpinCollLock". This is because agg cursors handle locking internally (hence the
// release), but the pin and unpin of the cursor must occur under the collection
// lock. We don't use our AutoGetCollectionForRead "ctx" to relock, because
// AutoGetCollectionForRead checks the sharding version (and we want the relock for
// the unpin to succeed even if the sharding version has changed).
//
// Note that we declare our locks before our ClientCursorPin, in order to ensure that
// the pin's destructor is called before the lock destructors (so that the unpin occurs
// under the lock).
std::unique_ptr<AutoGetCollectionForRead> ctx;
std::unique_ptr<Lock::DBLock> unpinDBLock;
std::unique_ptr<Lock::CollectionLock> unpinCollLock;
CursorManager* cursorManager;
if (request.nss.isListIndexesCursorNS() || request.nss.isListCollectionsCursorNS()) {
cursorManager = CursorManager::getGlobalCursorManager();
} else {
ctx = stdx::make_unique<AutoGetCollectionOrViewForRead>(txn, request.nss);
auto viewCtx = static_cast<AutoGetCollectionOrViewForRead*>(ctx.get());
Collection* collection = ctx->getCollection();
if (!collection) {
// Rewrite a getMore on a view to a getMore on the original underlying collection.
// If the view no longer exists, or has been rewritten, the cursor id will be
// unknown, resulting in an appropriate error.
if (viewCtx->getView()) {
auto resolved =
viewCtx->getDb()->getViewCatalog()->resolveView(txn, request.nss);
if (!resolved.isOK()) {
return appendCommandStatus(result, resolved.getStatus());
}
viewCtx->releaseLocksForView();
// Only one shardversion can be set at a time for an operation, so unset it
// here to allow setting it on the underlying namespace.
OperationShardingState::get(txn).unsetShardVersion(request.nss);
GetMoreRequest newRequest(resolved.getValue().getNamespace(),
request.cursorid,
request.batchSize,
request.awaitDataTimeout,
request.term,
request.lastKnownCommittedOpTime);
bool retVal = runParsed(txn, origNss, newRequest, cmdObj, errmsg, result);
{
// Set the namespace of the curop back to the view namespace so ctx records
// stats on this view namespace on destruction.
stdx::lock_guard<Client>(*txn->getClient());
curOp->setNS_inlock(origNss.ns());
}
return retVal;
}
return appendCommandStatus(result,
Status(ErrorCodes::OperationFailed,
"collection dropped between getMore calls"));
}
cursorManager = collection->getCursorManager();
}
auto ccPin = cursorManager->pinCursor(request.cursorid);
if (!ccPin.isOK()) {
// We didn't find the cursor.
return appendCommandStatus(result, ccPin.getStatus());
}
ClientCursor* cursor = ccPin.getValue().getCursor();
// If the fail point is enabled, busy wait until it is disabled. We unlock and re-acquire
// the locks periodically in order to avoid deadlock (see SERVER-21997 for details).
while (MONGO_FAIL_POINT(keepCursorPinnedDuringGetMore)) {
invariant(ctx);
invariant(!unpinDBLock);
invariant(!unpinCollLock);
sleepFor(Milliseconds(10));
ctx.reset();
ctx = stdx::make_unique<AutoGetCollectionForRead>(txn, request.nss);
}
if (request.nss.ns() != cursor->ns()) {
return appendCommandStatus(
result,
Status(ErrorCodes::Unauthorized,
str::stream() << "Requested getMore on namespace '" << request.nss.ns()
<< "', but cursor belongs to a different namespace"));
}
if (request.nss.isOplog() && MONGO_FAIL_POINT(rsStopGetMoreCmd)) {
return appendCommandStatus(
result,
Status(ErrorCodes::CommandFailed,
str::stream() << "getMore on " << request.nss.ns()
<< " rejected due to active fail point rsStopGetMoreCmd"));
}
// Validation related to awaitData.
if (isCursorAwaitData(cursor)) {
invariant(isCursorTailable(cursor));
if (cursor->isAggCursor()) {
Status status(ErrorCodes::BadValue,
"awaitData cannot be set on an aggregation cursor");
return appendCommandStatus(result, status);
}
}
if (request.awaitDataTimeout && !isCursorAwaitData(cursor)) {
Status status(ErrorCodes::BadValue,
"cannot set maxTimeMS on getMore command for a non-awaitData cursor");
return appendCommandStatus(result, status);
}
// On early return, get rid of the cursor.
ScopeGuard cursorFreer =
MakeGuard(&GetMoreCmd::cleanupCursor, txn, &ccPin.getValue(), request);
if (cursor->isReadCommitted())
uassertStatusOK(txn->recoveryUnit()->setReadFromMajorityCommittedSnapshot());
// Reset timeout timer on the cursor since the cursor is still in use.
cursor->resetIdleTime();
const bool hasOwnMaxTime = txn->hasDeadline();
if (!hasOwnMaxTime) {
// 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 (isCursorAwaitData(cursor)) {
uassert(40117,
"Illegal attempt to set operation deadline within DBDirectClient",
!txn->getClient()->isInDirectClient());
txn->setDeadlineAfterNowBy(Seconds{1});
} else if (cursor->getLeftoverMaxTimeMicros() < Microseconds::max()) {
uassert(40118,
"Illegal attempt to set operation deadline within DBDirectClient",
!txn->getClient()->isInDirectClient());
txn->setDeadlineAfterNowBy(cursor->getLeftoverMaxTimeMicros());
}
}
txn->checkForInterrupt(); // May trigger maxTimeAlwaysTimeOut fail point.
if (cursor->isAggCursor()) {
// Agg cursors handle their own locking internally.
ctx.reset(); // unlocks
}
PlanExecutor* exec = cursor->getExecutor();
exec->reattachToOperationContext(txn);
exec->restoreState();
auto planSummary = Explain::getPlanSummary(exec);
{
stdx::lock_guard<Client>(*txn->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->getQuery();
if (!originatingCommand.isEmpty()) {
curOp->setOriginatingCommand_inlock(originatingCommand);
}
}
uint64_t notifierVersion = 0;
std::shared_ptr<CappedInsertNotifier> notifier;
if (isCursorAwaitData(cursor)) {
invariant(ctx->getCollection()->isCapped());
// Retrieve the notifier which we will wait on until new data arrives. We make sure
// to do this in the lock because once we drop the lock it is possible for the
// collection to become invalid. The notifier itself will outlive the collection if
// the collection is dropped, as we keep a shared_ptr to it.
notifier = ctx->getCollection()->getCappedInsertNotifier();
// Must get the version before we call generateBatch in case a write comes in after
// that call and before we call wait on the notifier.
notifierVersion = notifier->getVersion();
}
CursorId respondWithId = 0;
CursorResponseBuilder nextBatch(/*isInitialResponse*/ false, &result);
BSONObj obj;
// generateBatch() will not initialize 'state' if it exceeds the time limiting generating
// the next batch for an awaitData cursor. In this case, 'state' should be
// PlanExecutor::ADVANCED, so we do not attempt to get another batch.
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);
Status batchStatus = generateBatch(cursor, request, &nextBatch, &state, &numResults);
if (!batchStatus.isOK()) {
return appendCommandStatus(result, batchStatus);
}
// If this is an await data cursor, and we hit EOF without generating any results, then
// we block waiting for new data to arrive.
if (isCursorAwaitData(cursor) && state == PlanExecutor::IS_EOF && numResults == 0) {
auto replCoord = repl::ReplicationCoordinator::get(txn);
// Return immediately if we need to update the commit time.
if (!request.lastKnownCommittedOpTime ||
(request.lastKnownCommittedOpTime == replCoord->getLastCommittedOpTime())) {
// Retrieve the notifier which we will wait on until new data arrives. We make sure
// to do this in the lock because once we drop the lock it is possible for the
// collection to become invalid. The notifier itself will outlive the collection if
// the collection is dropped, as we keep a shared_ptr to it.
auto notifier = ctx->getCollection()->getCappedInsertNotifier();
// Save the PlanExecutor and drop our locks.
exec->saveState();
ctx.reset();
// Block waiting for data.
const auto timeout = txn->getRemainingMaxTimeMicros();
notifier->wait(notifierVersion, timeout);
notifier.reset();
// Set expected latency to match wait time. This makes sure the logs aren't spammed
// by awaitData queries that exceed slowms due to blocking on the
// CappedInsertNotifier.
curOp->setExpectedLatencyMs(durationCount<Milliseconds>(timeout));
ctx.reset(new AutoGetCollectionForRead(txn, request.nss));
exec->restoreState();
// We woke up because either the timed_wait expired, or there was more data. Either
// way, attempt to generate another batch of results.
batchStatus = generateBatch(cursor, request, &nextBatch, &state, &numResults);
if (!batchStatus.isOK()) {
return appendCommandStatus(result, 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, both in the original request and
// subsequent getMore. The reason for this is that aggregation's 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 (!cursor->isAggCursor() && curOp->shouldDBProfile()) {
BSONObjBuilder execStatsBob;
Explain::getWinningPlanStats(exec, &execStatsBob);
curOp->debug().execStats = execStatsBob.obj();
}
if (shouldSaveCursorGetMore(state, exec, isCursorTailable(cursor))) {
respondWithId = request.cursorid;
exec->saveState();
exec->detachFromOperationContext();
// If maxTimeMS was set directly on the getMore rather than being rolled over
// from a previous find, then don't roll remaining micros over to the next
// getMore.
if (!hasOwnMaxTime) {
cursor->setLeftoverMaxTimeMicros(txn->getRemainingMaxTimeMicros());
}
cursor->incPos(numResults);
} else {
curOp->debug().cursorExhausted = true;
}
// Respond with the originally requested namespace, even if this is a getMore over a view
// that was resolved to a different backing namespace.
nextBatch.done(respondWithId, origNss.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();
// If we are operating on an aggregation cursor, then we dropped our collection lock
// earlier and need to reacquire it in order to clean up our ClientCursorPin.
if (cursor->isAggCursor()) {
invariant(NULL == ctx.get());
unpinDBLock.reset(new Lock::DBLock(txn->lockState(), request.nss.db(), MODE_IS));
unpinCollLock.reset(
new Lock::CollectionLock(txn->lockState(), request.nss.ns(), MODE_IS));
}
}
return true;
}
bool run(OperationContext* txn,
const std::string& dbname,
BSONObj& cmdObj,
int options,
std::string& errmsg,
BSONObjBuilder& result) override {
// Counted as a getMore, not as a command.
globalOpCounters.gotGetMore();
if (txn->getClient()->isInDirectClient()) {
return appendCommandStatus(
result,
Status(ErrorCodes::IllegalOperation, "Cannot run getMore command from eval()"));
}
StatusWith<GetMoreRequest> parsedRequest = GetMoreRequest::parseFromBSON(dbname, cmdObj);
if (!parsedRequest.isOK()) {
return appendCommandStatus(result, parsedRequest.getStatus());
}
auto request = parsedRequest.getValue();
return runParsed(txn, request.nss, request, cmdObj, errmsg, 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(ClientCursor* cursor,
const GetMoreRequest& request,
CursorResponseBuilder* nextBatch,
PlanExecutor::ExecState* state,
long long* numResults) {
PlanExecutor* exec = cursor->getExecutor();
const bool isAwaitData = isCursorAwaitData(cursor);
// 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;
}
// Add result to output buffer.
nextBatch->append(obj);
(*numResults)++;
}
} catch (const UserException& except) {
if (isAwaitData && except.getCode() == ErrorCodes::ExceededTimeLimit) {
// We ignore exceptions from interrupt points due to max time expiry for
// awaitData cursors.
} else {
throw;
}
}
if (PlanExecutor::FAILURE == *state || PlanExecutor::DEAD == *state) {
nextBatch->abandon();
error() << "GetMore command executor error: " << PlanExecutor::statestr(*state)
<< ", stats: " << redact(Explain::getWinningPlanStats(exec));
return Status(ErrorCodes::OperationFailed,
str::stream() << "GetMore command executor error: "
<< WorkingSetCommon::toStatusString(obj));
}
return Status::OK();
}
/**
* Called via a ScopeGuard on early return in order to ensure that the ClientCursor gets
* cleaned up properly.
*/
static void cleanupCursor(OperationContext* txn,
ClientCursorPin* ccPin,
const GetMoreRequest& request) {
ClientCursor* cursor = ccPin->getCursor();
std::unique_ptr<Lock::DBLock> unpinDBLock;
std::unique_ptr<Lock::CollectionLock> unpinCollLock;
if (cursor->isAggCursor()) {
unpinDBLock.reset(new Lock::DBLock(txn->lockState(), request.nss.db(), MODE_IS));
unpinCollLock.reset(
new Lock::CollectionLock(txn->lockState(), request.nss.ns(), MODE_IS));
}
ccPin->deleteUnderlying();
}
} getMoreCmd;
} // namespace mongo
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