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Keep SnapshotMetadata in memory

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Summary:
Instead of asking rocksdb for snapshot metadata, keep it in memory for
faster access.

Reviewers: ipaljak

Reviewed By: ipaljak

Subscribers: pullbot

Differential Revision: https://phabricator.memgraph.io/D2075
This commit is contained in:
Matija Santl 2019-05-21 13:37:40 +02:00
parent f2cc41fa59
commit e1fdb85a34
2 changed files with 29 additions and 31 deletions

58
src/raft/raft_server.cpp
View File

@ -54,11 +54,11 @@ RaftServer::RaftServer(uint16_t server_id, const std::string &durability_dir,
void RaftServer::Start() {
if (db_recover_on_startup_) {
auto snapshot_metadata = GetSnapshotMetadata();
if (snapshot_metadata) {
RecoverSnapshot(snapshot_metadata->snapshot_filename);
last_applied_ = snapshot_metadata->last_included_index;
commit_index_ = snapshot_metadata->last_included_index;
snapshot_metadata_ = GetSnapshotMetadata();
if (snapshot_metadata_) {
RecoverSnapshot(snapshot_metadata_->snapshot_filename);
last_applied_ = snapshot_metadata_->last_included_index;
commit_index_ = snapshot_metadata_->last_included_index;
}
} else {
// We need to clear persisted data if we don't want any recovery.
@ -169,17 +169,15 @@ void RaftServer::Start() {
// term, then they store the same command.
// - If two entries in different logs have the same index and term,
// then the logs are identical in all preceding entries.
auto snapshot_metadata = GetSnapshotMetadata();
if (snapshot_metadata &&
snapshot_metadata->last_included_index == req.prev_log_index) {
if (req.prev_log_term != snapshot_metadata->last_included_term) {
if (snapshot_metadata_ &&
snapshot_metadata_->last_included_index == req.prev_log_index) {
if (req.prev_log_term != snapshot_metadata_->last_included_term) {
AppendEntriesRes res(false, current_term_);
slk::Save(res, res_builder);
return;
}
} else if (snapshot_metadata &&
snapshot_metadata->last_included_index > req.prev_log_index) {
} else if (snapshot_metadata_ &&
snapshot_metadata_->last_included_index > req.prev_log_index) {
LOG(ERROR) << "Received entries that are already commited and have been "
"compacted";
AppendEntriesRes res(false, current_term_);
@ -413,6 +411,9 @@ void RaftServer::PersistSnapshotMetadata(
slk::Save(snapshot_metadata, &builder);
builder.Finalize();
disk_storage_.Put(kSnapshotMetadataKey, stream.str());
// Keep the metadata in memory for faster access.
snapshot_metadata_.emplace(snapshot_metadata);
}
void RaftServer::AppendToLog(const tx::TransactionId &tx_id,
@ -579,10 +580,9 @@ void RaftServer::Transition(const Mode &new_mode) {
// Re-apply raft log.
uint64_t starting_index = 1;
auto snapshot_metadata = GetSnapshotMetadata();
if (snapshot_metadata) {
RecoverSnapshot(snapshot_metadata->snapshot_filename);
starting_index = snapshot_metadata->last_included_index + 1;
if (snapshot_metadata_) {
RecoverSnapshot(snapshot_metadata_->snapshot_filename);
starting_index = snapshot_metadata_->last_included_index + 1;
}
for (uint64_t i = starting_index; i <= commit_index_; ++i) {
@ -725,13 +725,11 @@ void RaftServer::AdvanceCommitIndex() {
void RaftServer::SendEntries(uint16_t peer_id,
std::unique_lock<std::mutex> *lock) {
auto snapshot_metadata = GetSnapshotMetadata();
if (snapshot_metadata &&
snapshot_metadata->last_included_index >= next_index_[peer_id]) {
SendSnapshot(peer_id, *snapshot_metadata, lock);
if (snapshot_metadata_ &&
snapshot_metadata_->last_included_index >= next_index_[peer_id]) {
SendSnapshot(peer_id, *snapshot_metadata_, lock);
} else {
SendLogEntries(peer_id, snapshot_metadata, lock);
SendLogEntries(peer_id, snapshot_metadata_, lock);
}
}
@ -1068,9 +1066,8 @@ void RaftServer::SnapshotThread() {
if (exiting_) break;
uint64_t committed_log_size = last_applied_;
auto snapshot_metadata = GetSnapshotMetadata();
if (snapshot_metadata) {
committed_log_size -= snapshot_metadata->last_included_index;
if (snapshot_metadata_) {
committed_log_size -= snapshot_metadata_->last_included_index;
}
// Compare the log size to the config
@ -1103,9 +1100,9 @@ void RaftServer::SnapshotThread() {
if (status) {
uint64_t log_compaction_start_index = 1;
if (snapshot_metadata) {
if (snapshot_metadata_) {
log_compaction_start_index =
snapshot_metadata->last_included_index + 1;
snapshot_metadata_->last_included_index + 1;
}
VLOG(40) << "[LogCompaction] Persisting snapshot metadata";
@ -1156,10 +1153,9 @@ bool RaftServer::HasMajorityVote() {
}
std::pair<uint64_t, uint64_t> RaftServer::LastEntryData() {
auto snapshot_metadata = GetSnapshotMetadata();
if (snapshot_metadata &&
snapshot_metadata->last_included_index == log_size_ - 1) {
return {log_size_, snapshot_metadata->last_included_term};
if (snapshot_metadata_ &&
snapshot_metadata_->last_included_index == log_size_ - 1) {
return {log_size_, snapshot_metadata_->last_included_term};
}
return {log_size_, GetLogEntry(log_size_ - 1).term};
}

2
src/raft/raft_server.hpp
View File

@ -289,6 +289,8 @@ class RaftServer final : public RaftInterface {
std::map<uint64_t, LogEntry> log_;
std::optional<SnapshotMetadata> snapshot_metadata_;
/// Recovers persistent data from disk and stores its in-memory copies
/// that insure faster read-only operations. This method should be called
/// on start-up. If parts of persistent data are missing, the method won't