diff options
Diffstat (limited to 'src/mongo/db/repl/oplog_fetcher.cpp')
| -rw-r--r-- | src/mongo/db/repl/oplog_fetcher.cpp | 76 |
1 files changed, 25 insertions, 51 deletions
diff --git a/src/mongo/db/repl/oplog_fetcher.cpp b/src/mongo/db/repl/oplog_fetcher.cpp index 73808edf3b8..ce499fd0c89 100644 --- a/src/mongo/db/repl/oplog_fetcher.cpp +++ b/src/mongo/db/repl/oplog_fetcher.cpp @@ -119,11 +119,8 @@ BSONObj makeMetadataObject(bool isV1ElectionProtocol) { * Checks the first batch of results from query. * 'documents' are the first batch of results returned from tailing the remote oplog. * 'lastFetched' optime and hash should be consistent with the predicate in the query. - * 'lastOpCommitted' is the OpTime of the most recently committed op of which this node is aware. * 'remoteLastOpApplied' is the last OpTime applied on the sync source. This is optional for * compatibility with 3.4 servers that do not send OplogQueryMetadata. - * 'remoteLastOpCommitted' is the OpTime of the most recently committed op of which the sync source - * is aware. * 'requiredRBID' is a RollbackID received when we chose the sync source that we use here to * guarantee we have not rolled back since we confirmed the sync source had our minValid. * 'remoteRBID' is a RollbackId for the sync source returned in this oplog query. This is optional @@ -132,17 +129,14 @@ BSONObj makeMetadataObject(bool isV1ElectionProtocol) { * oplog to be ahead of ours. If false, the sync source's oplog is allowed to be at the same point * as ours, but still cannot be behind ours. * - * TODO (SERVER-27668): Make remoteLastOpApplied, remoteLastOpCommitted, and remoteRBID - * non-optional. + * TODO (SERVER-27668): Make remoteLastOpApplied and remoteRBID non-optional in mongodb 3.8. * * Returns OplogStartMissing if we cannot find the optime of the last fetched operation in * the remote oplog. */ Status checkRemoteOplogStart(const Fetcher::Documents& documents, OpTimeWithHash lastFetched, - OpTime lastOpCommitted, boost::optional<OpTime> remoteLastOpApplied, - boost::optional<OpTime> remoteLastOpCommitted, int requiredRBID, boost::optional<int> remoteRBID, bool requireFresherSyncSource) { @@ -166,49 +160,34 @@ Status checkRemoteOplogStart(const Fetcher::Documents& documents, } } - // The sync source could be behind us if it rolled back after we selected it. We could have - // failed to detect the rollback if it occurred between sync source selection (when we check the - // candidate is ahead of us) and sync source resolution (when we got 'requiredRBID'). If the - // sync source is now behind us, choose a new sync source to prevent going into rollback. - if (remoteLastOpApplied && (*remoteLastOpApplied < lastFetched.opTime)) { + // The SyncSourceResolver never checks that the sync source candidate is actually ahead of + // us. Rather than have it check there with an extra network roundtrip, we check here. + if (requireFresherSyncSource && remoteLastOpApplied && + (*remoteLastOpApplied <= lastFetched.opTime)) { return Status(ErrorCodes::InvalidSyncSource, str::stream() << "Sync source's last applied OpTime " << remoteLastOpApplied->toString() - << " is older than our last fetched OpTime " + << " is not greater than our last fetched OpTime " << lastFetched.opTime.toString() << ". Choosing new sync source."); - } - - // If 'requireFresherSyncSource' is true, we must check that the sync source's - // lastApplied/lastOpCommitted is ahead of us to prevent forming a cycle. Although we check for - // this condition in sync source selection, if an undetected rollback occurred between sync - // source selection and sync source resolution, this condition may no longer hold. - // 'requireFresherSyncSource' is false for initial sync, since no other node can sync off an - // initial syncing node, so we do not need to check for cycles. In addition, it would be - // problematic to check this condition for initial sync, since the 'lastFetched' OpTime will - // almost always equal the 'remoteLastApplied', since we fetch the sync source's last applied - // OpTime to determine where to start our OplogFetcher. - if (requireFresherSyncSource && remoteLastOpApplied && remoteLastOpCommitted && - std::tie(*remoteLastOpApplied, *remoteLastOpCommitted) <= - std::tie(lastFetched.opTime, lastOpCommitted)) { + } else if (remoteLastOpApplied && (*remoteLastOpApplied < lastFetched.opTime)) { + // In initial sync, the lastFetched OpTime will almost always equal the remoteLastOpApplied + // since we fetch the sync source's last applied OpTime to determine where to start our + // OplogFetcher. This is fine since no other node can sync off of an initial syncing node + // and thus cannot form a sync source cycle. To account for this, we must relax the + // constraint on our sync source being fresher. return Status(ErrorCodes::InvalidSyncSource, - str::stream() - << "Sync source cannot be behind me, and if I am up-to-date with the " - "sync source, it must have a higher lastOpCommitted. " - << "My last fetched oplog optime: " - << lastFetched.opTime.toString() - << ", latest oplog optime of sync source: " - << remoteLastOpApplied->toString() - << ", my lastOpCommitted: " - << lastOpCommitted.toString() - << ", lastOpCommitted of sync source: " - << remoteLastOpCommitted->toString()); + str::stream() << "Sync source's last applied OpTime " + << remoteLastOpApplied->toString() + << " is older than our last fetched OpTime " + << lastFetched.opTime.toString() + << ". Choosing new sync source."); } - // At this point we know that our sync source has our minValid and is not behind us, so if our + // At this point we know that our sync source has our minValid and is ahead of us, so if our // history diverges from our sync source's we should prefer its history and roll back ours. - // Since we checked for rollback and our sync source is not behind us, an empty batch means that + // Since we checked for rollback and our sync source is ahead of us, an empty batch means that // we have a higher timestamp on our last fetched OpTime than our sync source's last applied // OpTime, but a lower term. When this occurs, we must roll back our inconsistent oplog entry. if (documents.empty()) { @@ -450,17 +429,12 @@ StatusWith<BSONObj> OplogFetcher::_onSuccessfulBatch(const Fetcher::QueryRespons auto remoteRBID = oqMetadata ? boost::make_optional(oqMetadata->getRBID()) : boost::none; auto remoteLastApplied = oqMetadata ? boost::make_optional(oqMetadata->getLastOpApplied()) : boost::none; - auto remoteLastOpCommitted = - oqMetadata ? boost::make_optional(oqMetadata->getLastOpCommitted()) : boost::none; - auto status = checkRemoteOplogStart( - documents, - lastFetched, - _dataReplicatorExternalState->getCurrentTermAndLastCommittedOpTime().opTime, - remoteLastApplied, - remoteLastOpCommitted, - _requiredRBID, - remoteRBID, - _requireFresherSyncSource); + auto status = checkRemoteOplogStart(documents, + lastFetched, + remoteLastApplied, + _requiredRBID, + remoteRBID, + _requireFresherSyncSource); if (!status.isOK()) { // Stop oplog fetcher and execute rollback if necessary. return status; |