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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.
*/
#define MONGO_LOG_DEFAULT_COMPONENT ::mongo::logger::LogComponent::kSharding
#include "mongo/platform/basic.h"
#include "mongo/db/s/session_catalog_migration_destination.h"
#include "mongo/bson/bsonobjbuilder.h"
#include "mongo/client/connection_string.h"
#include "mongo/db/concurrency/d_concurrency.h"
#include "mongo/db/concurrency/write_conflict_exception.h"
#include "mongo/db/logical_session_id.h"
#include "mongo/db/repl/oplog.h"
#include "mongo/db/repl/oplog_entry.h"
#include "mongo/db/s/migration_session_id.h"
#include "mongo/db/session_catalog_mongod.h"
#include "mongo/db/transaction_participant.h"
#include "mongo/db/write_concern.h"
#include "mongo/s/client/shard_registry.h"
#include "mongo/s/grid.h"
#include "mongo/s/shard_id.h"
#include "mongo/stdx/functional.h"
#include "mongo/util/log.h"
namespace mongo {
namespace {
const auto kOplogField = "oplog";
const WriteConcernOptions kMajorityWC(WriteConcernOptions::kMajority,
WriteConcernOptions::SyncMode::UNSET,
Milliseconds(0));
struct ProcessOplogResult {
LogicalSessionId sessionId;
TxnNumber txnNum;
repl::OpTime oplogTime;
bool isPrePostImage = false;
};
/**
* Returns the command request to extract session information from the source shard.
*/
BSONObj buildMigrateSessionCmd(const MigrationSessionId& migrationSessionId) {
BSONObjBuilder builder;
builder.append("_getNextSessionMods", 1);
migrationSessionId.append(&builder);
return builder.obj();
}
/**
* Determines whether the oplog entry has a link to either preImage/postImage and return a new
* oplogLink that contains the same link, but pointing to lastResult.oplogTime. For example, if
* entry has link to preImageTs, this returns an oplogLink with preImageTs pointing to
* lastResult.oplogTime.
*
* It is an error to have both preImage and postImage as well as not having them at all.
*/
repl::OplogLink extractPrePostImageTs(const ProcessOplogResult& lastResult,
const repl::OplogEntry& entry) {
repl::OplogLink oplogLink;
if (!lastResult.isPrePostImage) {
uassert(40628,
str::stream() << "expected oplog with ts: " << entry.getTimestamp().toString()
<< " to not have "
<< repl::OplogEntryBase::kPreImageOpTimeFieldName
<< " or "
<< repl::OplogEntryBase::kPostImageOpTimeFieldName,
!entry.getPreImageOpTime() && !entry.getPostImageOpTime());
return oplogLink;
}
invariant(!lastResult.oplogTime.isNull());
const auto& sessionInfo = entry.getOperationSessionInfo();
const auto sessionId = *sessionInfo.getSessionId();
const auto txnNum = *sessionInfo.getTxnNumber();
uassert(40629,
str::stream() << "expected oplog with ts: " << entry.getTimestamp().toString() << ": "
<< redact(entry.toBSON())
<< " to have session: "
<< lastResult.sessionId,
lastResult.sessionId == sessionId);
uassert(40630,
str::stream() << "expected oplog with ts: " << entry.getTimestamp().toString() << ": "
<< redact(entry.toBSON())
<< " to have txnNumber: "
<< lastResult.txnNum,
lastResult.txnNum == txnNum);
if (entry.getPreImageOpTime()) {
oplogLink.preImageOpTime = lastResult.oplogTime;
} else if (entry.getPostImageOpTime()) {
oplogLink.postImageOpTime = lastResult.oplogTime;
} else {
uasserted(40631,
str::stream() << "expected oplog with opTime: " << entry.getOpTime().toString()
<< ": "
<< redact(entry.toBSON())
<< " to have either "
<< repl::OplogEntryBase::kPreImageOpTimeFieldName
<< " or "
<< repl::OplogEntryBase::kPostImageOpTimeFieldName);
}
return oplogLink;
}
/**
* Parses the oplog into an oplog entry and makes sure that it contains the expected fields.
*/
repl::OplogEntry parseOplog(const BSONObj& oplogBSON) {
auto oplogEntry = uassertStatusOK(repl::OplogEntry::parse(oplogBSON));
// Session oplog entries must always contain wall clock time, because we will not be
// transferring anything from a previous version of the server
invariant(oplogEntry.getWallClockTime());
const auto& sessionInfo = oplogEntry.getOperationSessionInfo();
uassert(ErrorCodes::UnsupportedFormat,
str::stream() << "oplog with opTime " << oplogEntry.getTimestamp().toString()
<< " does not have sessionId: "
<< redact(oplogBSON),
sessionInfo.getSessionId());
uassert(ErrorCodes::UnsupportedFormat,
str::stream() << "oplog with opTime " << oplogEntry.getTimestamp().toString()
<< " does not have txnNumber: "
<< redact(oplogBSON),
sessionInfo.getTxnNumber());
uassert(ErrorCodes::UnsupportedFormat,
str::stream() << "oplog with opTime " << oplogEntry.getTimestamp().toString()
<< " does not have stmtId: "
<< redact(oplogBSON),
oplogEntry.getStatementId());
return oplogEntry;
}
/**
* Gets the next batch of oplog entries from the source shard.
*/
BSONObj getNextSessionOplogBatch(OperationContext* opCtx,
const ShardId& fromShard,
const MigrationSessionId& migrationSessionId) {
auto shardStatus = Grid::get(opCtx)->shardRegistry()->getShard(opCtx, fromShard);
uassertStatusOK(shardStatus.getStatus());
auto shard = shardStatus.getValue();
auto responseStatus = shard->runCommand(opCtx,
ReadPreferenceSetting(ReadPreference::PrimaryOnly),
"admin",
buildMigrateSessionCmd(migrationSessionId),
Shard::RetryPolicy::kNoRetry);
uassertStatusOK(responseStatus.getStatus());
uassertStatusOK(responseStatus.getValue().commandStatus);
auto result = responseStatus.getValue().response;
auto oplogElement = result[kOplogField];
uassert(ErrorCodes::FailedToParse,
"_getNextSessionMods response does not have the 'oplog' field as array",
oplogElement.type() == Array);
return result;
}
/**
* Insert a new oplog entry by converting the oplogBSON into type 'n' oplog with the session
* information. The new oplogEntry will also link to prePostImageTs if not null.
*/
ProcessOplogResult processSessionOplog(const BSONObj& oplogBSON,
const ProcessOplogResult& lastResult) {
auto oplogEntry = parseOplog(oplogBSON);
const auto& sessionInfo = oplogEntry.getOperationSessionInfo();
ProcessOplogResult result;
result.sessionId = *sessionInfo.getSessionId();
result.txnNum = *sessionInfo.getTxnNumber();
BSONObj object2;
if (oplogEntry.getOpType() == repl::OpTypeEnum::kNoop) {
// Note: Oplog is already no-op type, no need to nest.
// There are two types of type 'n' oplog format expected here:
// (1) Oplog entries that has been transformed by a previous migration into a
// nested oplog. In this case, o field contains {$sessionMigrateInfo: 1}
// and o2 field contains the details of the original oplog.
// (2) Oplog entries that contains the pre/post-image information of a
// findAndModify operation. In this case, o field contains the relevant info
// and o2 will be empty.
if (oplogEntry.getObject2()) {
object2 = *oplogEntry.getObject2();
}
if (object2.isEmpty()) {
result.isPrePostImage = true;
uassert(40632,
str::stream() << "Can't handle 2 pre/post image oplog in a row. Prevoius oplog "
<< lastResult.oplogTime.getTimestamp().toString()
<< ", oplog ts: "
<< oplogEntry.getTimestamp().toString()
<< ": "
<< oplogBSON,
!lastResult.isPrePostImage);
}
} else {
object2 = oplogBSON; // TODO: strip redundant info?
}
const auto stmtId = *oplogEntry.getStatementId();
auto uniqueOpCtx = cc().makeOperationContext();
auto opCtx = uniqueOpCtx.get();
opCtx->setLogicalSessionId(result.sessionId);
opCtx->setTxnNumber(result.txnNum);
MongoDOperationContextSession ocs(opCtx);
auto txnParticipant = TransactionParticipant::get(opCtx);
txnParticipant->beginOrContinue(result.txnNum, boost::none, boost::none);
try {
if (txnParticipant->checkStatementExecuted(stmtId)) {
// Skip the incoming statement because it has already been logged locally
return lastResult;
}
} catch (const DBException& ex) {
// If the transaction chain was truncated on the recipient shard, then we are most likely
// copying from a session that hasn't been touched on the recipient shard for a very long
// time but could be recent on the donor.
//
// We continue copying regardless to get the entire transaction from the donor.
if (ex.code() != ErrorCodes::IncompleteTransactionHistory) {
throw;
}
if (stmtId == kIncompleteHistoryStmtId) {
// No need to log entries for transactions whose history has been truncated
return lastResult;
}
}
BSONObj object(result.isPrePostImage
? oplogEntry.getObject()
: BSON(SessionCatalogMigrationDestination::kSessionMigrateOplogTag << 1));
auto oplogLink = extractPrePostImageTs(lastResult, oplogEntry);
oplogLink.prevOpTime = txnParticipant->getLastWriteOpTime();
writeConflictRetry(
opCtx,
"SessionOplogMigration",
NamespaceString::kSessionTransactionsTableNamespace.ns(),
[&] {
// Need to take global lock here so repl::logOp will not unlock it and trigger the
// invariant that disallows unlocking global lock while inside a WUOW. Grab a DBLock
// here instead of plain GlobalLock to make sure the MMAPV1 flush lock will be
// lock/unlocked correctly. Take the transaction table db lock to ensure the same lock
// ordering with normal replicated updates to the table.
Lock::DBLock lk(
opCtx, NamespaceString::kSessionTransactionsTableNamespace.db(), MODE_IX);
WriteUnitOfWork wunit(opCtx);
result.oplogTime = repl::logOp(opCtx,
"n",
oplogEntry.getNss(),
oplogEntry.getUuid(),
object,
&object2,
true,
*oplogEntry.getWallClockTime(),
sessionInfo,
stmtId,
oplogLink,
false /* prepare */,
OplogSlot());
const auto& oplogOpTime = result.oplogTime;
uassert(40633,
str::stream() << "Failed to create new oplog entry for oplog with opTime: "
<< oplogEntry.getOpTime().toString()
<< ": "
<< redact(oplogBSON),
!oplogOpTime.isNull());
// Do not call onWriteOpCompletedOnPrimary if we inserted a pre/post image, because the
// next oplog will contain the real operation
if (!result.isPrePostImage) {
txnParticipant->onMigrateCompletedOnPrimary(
opCtx, result.txnNum, {stmtId}, oplogOpTime, *oplogEntry.getWallClockTime());
}
wunit.commit();
});
return result;
}
} // namespace
const char SessionCatalogMigrationDestination::kSessionMigrateOplogTag[] = "$sessionMigrateInfo";
SessionCatalogMigrationDestination::SessionCatalogMigrationDestination(
ShardId fromShard, MigrationSessionId migrationSessionId)
: _fromShard(std::move(fromShard)), _migrationSessionId(std::move(migrationSessionId)) {}
SessionCatalogMigrationDestination::~SessionCatalogMigrationDestination() {
if (_thread.joinable()) {
_errorOccurred("Destructor cleaning up thread");
_thread.join();
}
}
void SessionCatalogMigrationDestination::start(ServiceContext* service) {
{
stdx::lock_guard<stdx::mutex> lk(_mutex);
invariant(_state == State::NotStarted);
_state = State::Migrating;
_isStateChanged.notify_all();
}
_thread = stdx::thread([=] {
try {
_retrieveSessionStateFromSource(service);
} catch (const DBException& ex) {
if (ex.code() == ErrorCodes::CommandNotFound) {
// TODO: remove this after v3.7
//
// This means that the donor shard is running at an older version so it is safe to
// just end this because there is no session information to transfer.
return;
}
_errorOccurred(ex.toString());
}
});
}
void SessionCatalogMigrationDestination::finish() {
stdx::lock_guard<stdx::mutex> lk(_mutex);
if (_state != State::ErrorOccurred) {
_state = State::Committing;
_isStateChanged.notify_all();
}
}
void SessionCatalogMigrationDestination::join() {
invariant(_thread.joinable());
_thread.join();
}
/**
* Outline:
*
* 1. Get oplog with session info from the source shard.
* 2. For each oplog entry, convert to type 'n' if not yet type 'n' while preserving all info
* needed for retryable writes.
* 3. Also update the sessionCatalog for every oplog entry.
* 4. Once the source shard returned an empty oplog buffer, it means that this should enter
* ReadyToCommit state and wait for the commit signal (by calling finish()).
* 5. Once finish() is called, keep on trying to get more oplog from the source shard until it
* returns an empty result again.
* 6. Wait for writes to be committed to majority of the replica set.
*/
void SessionCatalogMigrationDestination::_retrieveSessionStateFromSource(ServiceContext* service) {
Client::initThread(
"sessionCatalogMigrationProducer-" + _migrationSessionId.toString(), service, nullptr);
bool oplogDrainedAfterCommiting = false;
ProcessOplogResult lastResult;
repl::OpTime lastOpTimeWaited;
while (true) {
{
stdx::lock_guard<stdx::mutex> lk(_mutex);
if (_state == State::ErrorOccurred) {
return;
}
}
BSONObj nextBatch;
BSONArray oplogArray;
{
auto uniqueCtx = cc().makeOperationContext();
auto opCtx = uniqueCtx.get();
nextBatch = getNextSessionOplogBatch(opCtx, _fromShard, _migrationSessionId);
oplogArray = BSONArray{nextBatch[kOplogField].Obj()};
if (oplogArray.isEmpty()) {
{
stdx::lock_guard<stdx::mutex> lk(_mutex);
if (_state == State::Committing) {
// The migration is considered done only when it gets an empty result from
// the source shard while this is in state committing. This is to make sure
// that it doesn't miss any new oplog created between the time window where
// this depleted the buffer from the source shard and receiving the commit
// command.
if (oplogDrainedAfterCommiting) {
break;
}
oplogDrainedAfterCommiting = true;
}
}
WriteConcernResult unusedWCResult;
uassertStatusOK(
waitForWriteConcern(opCtx, lastResult.oplogTime, kMajorityWC, &unusedWCResult));
// We depleted the buffer at least once, transition to ready for commit.
{
stdx::lock_guard<stdx::mutex> lk(_mutex);
// Note: only transition to "ready to commit" if state is not error/force stop.
if (_state == State::Migrating) {
_state = State::ReadyToCommit;
_isStateChanged.notify_all();
}
}
if (lastOpTimeWaited == lastResult.oplogTime) {
// We got an empty result at least twice in a row from the source shard so space
// it
// out a little bit so we don't hammer the shard
opCtx->sleepFor(Milliseconds(200));
}
lastOpTimeWaited = lastResult.oplogTime;
}
}
for (BSONArrayIteratorSorted oplogIter(oplogArray); oplogIter.more();) {
try {
lastResult = processSessionOplog(oplogIter.next().Obj(), lastResult);
} catch (const ExceptionFor<ErrorCodes::ConfigurationInProgress>&) {
// This means that the server has a newer txnNumber than the oplog being
// migrated, so just skip it
continue;
} catch (const ExceptionFor<ErrorCodes::TransactionTooOld>&) {
// This means that the server has a newer txnNumber than the oplog being
// migrated, so just skip it
continue;
}
}
}
WriteConcernResult unusedWCResult;
auto uniqueOpCtx = cc().makeOperationContext();
uassertStatusOK(
waitForWriteConcern(uniqueOpCtx.get(), lastResult.oplogTime, kMajorityWC, &unusedWCResult));
{
stdx::lock_guard<stdx::mutex> lk(_mutex);
_state = State::Done;
_isStateChanged.notify_all();
}
}
std::string SessionCatalogMigrationDestination::getErrMsg() {
stdx::lock_guard<stdx::mutex> lk(_mutex);
return _errMsg;
}
void SessionCatalogMigrationDestination::_errorOccurred(StringData errMsg) {
stdx::lock_guard<stdx::mutex> lk(_mutex);
_state = State::ErrorOccurred;
_errMsg = errMsg.toString();
_isStateChanged.notify_all();
}
SessionCatalogMigrationDestination::State SessionCatalogMigrationDestination::getState() {
stdx::lock_guard<stdx::mutex> lk(_mutex);
return _state;
}
void SessionCatalogMigrationDestination::forceFail(StringData errMsg) {
_errorOccurred(errMsg);
}
} // namespace mongo
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