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/**
* Copyright (C) 2018-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.h"
#include "mongo/db/concurrency/write_conflict_exception.h"
#include "mongo/db/curop.h"
#include "mongo/db/curop_failpoint_helpers.h"
#include "mongo/db/operation_context.h"
#include "mongo/db/query/query_knobs_gen.h"
#include "mongo/db/service_context.h"
#include "mongo/util/fail_point_service.h"
#include "mongo/util/scopeguard.h"
#include "mongo/util/time_support.h"
namespace mongo {
namespace {
MONGO_FAIL_POINT_DEFINE(setInterruptOnlyPlansCheckForInterruptHang);
} // namespace
PlanYieldPolicy::PlanYieldPolicy(PlanExecutor* exec, PlanExecutor::YieldPolicy policy)
: _policy(exec->getOpCtx()->lockState()->isGlobalLockedRecursively() ? PlanExecutor::NO_YIELD
: policy),
_forceYield(false),
_elapsedTracker(exec->getOpCtx()->getServiceContext()->getFastClockSource(),
internalQueryExecYieldIterations.load(),
Milliseconds(internalQueryExecYieldPeriodMS.load())),
_planYielding(exec) {}
PlanYieldPolicy::PlanYieldPolicy(PlanExecutor::YieldPolicy policy, ClockSource* cs)
: _policy(policy),
_forceYield(false),
_elapsedTracker(cs,
internalQueryExecYieldIterations.load(),
Milliseconds(internalQueryExecYieldPeriodMS.load())),
_planYielding(nullptr) {}
bool PlanYieldPolicy::shouldYieldOrInterrupt() {
if (_policy == PlanExecutor::INTERRUPT_ONLY) {
return _elapsedTracker.intervalHasElapsed();
}
if (!canAutoYield())
return false;
invariant(!_planYielding->getOpCtx()->lockState()->inAWriteUnitOfWork());
if (_forceYield)
return true;
return _elapsedTracker.intervalHasElapsed();
}
void PlanYieldPolicy::resetTimer() {
_elapsedTracker.resetLastTime();
}
Status PlanYieldPolicy::yieldOrInterrupt(std::function<void()> whileYieldingFn) {
invariant(_planYielding);
if (_policy == PlanExecutor::INTERRUPT_ONLY) {
ON_BLOCK_EXIT([this]() { resetTimer(); });
OperationContext* opCtx = _planYielding->getOpCtx();
invariant(opCtx);
// If the 'setInterruptOnlyPlansCheckForInterruptHang' fail point is enabled, set the 'msg'
// field of this operation's CurOp to signal that we've hit this point.
if (MONGO_FAIL_POINT(setInterruptOnlyPlansCheckForInterruptHang)) {
CurOpFailpointHelpers::waitWhileFailPointEnabled(
&setInterruptOnlyPlansCheckForInterruptHang,
opCtx,
"setInterruptOnlyPlansCheckForInterruptHang");
}
return opCtx->checkForInterruptNoAssert();
}
invariant(canAutoYield());
// After we finish yielding (or in any early return), call resetTimer() to prevent yielding
// again right away. We delay the resetTimer() call so that the clock doesn't start ticking
// until after we return from the yield.
ON_BLOCK_EXIT([this]() { resetTimer(); });
_forceYield = false;
OperationContext* opCtx = _planYielding->getOpCtx();
invariant(opCtx);
invariant(!opCtx->lockState()->inAWriteUnitOfWork());
// Can't use writeConflictRetry since we need to call saveState before reseting the transaction.
for (int attempt = 1; true; attempt++) {
try {
try {
_planYielding->saveState();
} catch (const WriteConflictException&) {
invariant(!"WriteConflictException not allowed in saveState");
}
if (_policy == PlanExecutor::WRITE_CONFLICT_RETRY_ONLY) {
// Just reset the snapshot. Leave all LockManager locks alone.
opCtx->recoveryUnit()->abandonSnapshot();
} else {
// Release and reacquire locks.
_yieldAllLocks(opCtx, whileYieldingFn, _planYielding->nss());
}
_planYielding->restoreStateWithoutRetrying();
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();
}
}
}
namespace {
MONGO_FAIL_POINT_DEFINE(setYieldAllLocksHang);
MONGO_FAIL_POINT_DEFINE(setYieldAllLocksWait);
} // namespace
void PlanYieldPolicy::_yieldAllLocks(OperationContext* opCtx,
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;
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 (_policy == PlanExecutor::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();
MONGO_FAIL_POINT_BLOCK(setYieldAllLocksHang, config) {
StringData ns{config.getData().getStringField("namespace")};
if (ns.empty() || ns == planExecNS.ns()) {
MONGO_FAIL_POINT_PAUSE_WHILE_SET(setYieldAllLocksHang);
}
}
MONGO_FAIL_POINT_BLOCK(setYieldAllLocksWait, customWait) {
const BSONObj& data = customWait.getData();
BSONElement customWaitNS = data["namespace"];
if (!customWaitNS || planExecNS.ns() == customWaitNS.str()) {
sleepFor(Milliseconds(data["waitForMillis"].numberInt()));
}
}
if (whileYieldingFn) {
whileYieldingFn();
}
locker->restoreLockState(opCtx, snapshot);
}
} // namespace mongo
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