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/**
* Copyright (C) 2020-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* 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
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* 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 Server Side 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.
*/
#include "mongo/platform/basic.h"
#include "mongo/db/query/plan_yield_policy_impl.h"
#include "mongo/db/concurrency/write_conflict_exception.h"
#include "mongo/db/curop.h"
#include "mongo/db/curop_failpoint_helpers.h"
#include "mongo/db/query/query_knobs_gen.h"
#include "mongo/db/service_context.h"
#include "mongo/db/storage/snapshot_helper.h"
#include "mongo/util/fail_point.h"
namespace mongo {
namespace {
MONGO_FAIL_POINT_DEFINE(setInterruptOnlyPlansCheckForInterruptHang);
} // namespace
PlanYieldPolicyImpl::PlanYieldPolicyImpl(PlanExecutorImpl* exec,
PlanYieldPolicy::YieldPolicy policy,
const Yieldable* yieldable)
: PlanYieldPolicy(exec->getOpCtx()->lockState()->isGlobalLockedRecursively()
? PlanYieldPolicy::YieldPolicy::NO_YIELD
: policy,
exec->getOpCtx()->getServiceContext()->getFastClockSource(),
internalQueryExecYieldIterations.load(),
Milliseconds{internalQueryExecYieldPeriodMS.load()}),
_planYielding(exec),
_yieldable(yieldable) {}
Status PlanYieldPolicyImpl::yield(OperationContext* opCtx, std::function<void()> whileYieldingFn) {
// Can't use writeConflictRetry since we need to call saveState before reseting the
// transaction.
for (int attempt = 1; true; attempt++) {
try {
// Saving and restoring state modifies _yieldable so make a copy before we start
const Yieldable* yieldable = _yieldable;
try {
_planYielding->saveState();
} catch (const WriteConflictException&) {
invariant(!"WriteConflictException not allowed in saveState");
}
if (getPolicy() == PlanYieldPolicy::YieldPolicy::WRITE_CONFLICT_RETRY_ONLY) {
// Just reset the snapshot. Leave all LockManager locks alone.
opCtx->recoveryUnit()->abandonSnapshot();
} else {
// Release and reacquire locks.
_yieldAllLocks(opCtx, yieldable, whileYieldingFn, _planYielding->nss());
}
_planYielding->restoreStateWithoutRetrying(yieldable);
return Status::OK();
} catch (const WriteConflictException&) {
CurOp::get(opCtx)->debug().additiveMetrics.incrementWriteConflicts(1);
WriteConflictException::logAndBackoff(
attempt, "plan execution restoreState", _planYielding->nss().ns());
// retry
} catch (...) {
// Errors other than write conflicts don't get retried, and should instead result in
// the PlanExecutor dying. We propagate all such errors as status codes.
return exceptionToStatus();
}
}
}
void PlanYieldPolicyImpl::_yieldAllLocks(OperationContext* opCtx,
const Yieldable* yieldable,
std::function<void()> whileYieldingFn,
const NamespaceString& planExecNS) {
// Things have to happen here in a specific order:
// * Release lock mgr locks
// * Check for interrupt (kill flag is set)
// * Call the whileYieldingFn
// * Reacquire lock mgr locks
Locker* locker = opCtx->lockState();
Locker::LockSnapshot snapshot;
if (yieldable) {
yieldable->yield();
}
auto unlocked = locker->saveLockStateAndUnlock(&snapshot);
// Attempt to check for interrupt while locks are not held, in order to discourage the
// assumption that locks will always be held when a Plan Executor returns an error.
if (getPolicy() == PlanYieldPolicy::YieldPolicy::YIELD_AUTO) {
opCtx->checkForInterrupt(); // throws
}
if (!unlocked) {
// Nothing was unlocked, just return, yielding is pointless.
return;
}
// Top-level locks are freed, release any potential low-level (storage engine-specific
// locks). If we are yielding, we are at a safe place to do so.
opCtx->recoveryUnit()->abandonSnapshot();
// Track the number of yields in CurOp.
CurOp::get(opCtx)->yielded();
handleDuringYieldFailpoints(opCtx, planExecNS);
if (whileYieldingFn) {
whileYieldingFn();
}
locker->restoreLockState(opCtx, snapshot);
if (yieldable) {
yieldable->restore();
}
// After yielding and reacquiring locks, the preconditions that were used to select our
// ReadSource initially need to be checked again. Queries hold an AutoGetCollectionForRead RAII
// lock for their lifetime, which may select a ReadSource based on state (e.g. replication
// state). After a query yields its locks, this state may have changed, invalidating our current
// choice of ReadSource. Using the same preconditions, change our ReadSource if necessary.
auto newReadSource = SnapshotHelper::getNewReadSource(opCtx, planExecNS);
if (newReadSource) {
opCtx->recoveryUnit()->setTimestampReadSource(*newReadSource);
}
}
void PlanYieldPolicyImpl::preCheckInterruptOnly(OperationContext* opCtx) {
// If the 'setInterruptOnlyPlansCheckForInterruptHang' fail point is enabled, set the
// 'failPointMsg' field of this operation's CurOp to signal that we've hit this point.
if (MONGO_unlikely(setInterruptOnlyPlansCheckForInterruptHang.shouldFail())) {
CurOpFailpointHelpers::waitWhileFailPointEnabled(
&setInterruptOnlyPlansCheckForInterruptHang,
opCtx,
"setInterruptOnlyPlansCheckForInterruptHang");
}
}
} // namespace mongo
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