Write ahead logging for rust applications. Write ahead logging is a crucial component for applications requiring data durability. Many times it is inefficient to flush and sync new data (or modifications to existing data) to on-disk data-structures, like an index. Write-ahead-logging facilitates by ingesting write operations by appending and syncing it to disk and allows applications to pre-process a batch of write-operations and write them to on-disk structures in the most efficient manner.

Goals

• Serialize write operations to an append only journal file.
• Generate monotonically increasing sequence-number and return the same to the application.
• Configurable limit for journal file, beyond which log files are rotate.
• Configurable fsync, for persistence guarantee.
• Iterate over all entries persisted in the log file in monotonically increasing seqno order.
• Range over a subset of entries, specified with start-seqno and end-seqno.
• Wal type is parameterized over a state type S. This is helpful for using Wal type to be used with consensus protocol like Raft.
• Concurrent readers and writers into single log instance.

Concurrency

A single log-instance can be cloned and shared among multiple threads for concurrent writing and reading. All write operations are serialized. While read operations and write-operation are mutually exclusive, concurrent reads are allowed.

Performance

Single threaded write performance with different payload size and fsync enabled.

payload	total-entries	elapsed-time	throughput
100	10000	31s	300/s
1000	10000	31s	300/s
10000	10000	31s	300/s
10000	1000	3.1s	300/s

Multi-threaded write performance with constant payload size of 100-bytes per operation and fsync enabled.

threads	total-entries	elapsed-time	throughput
1	10000	31s	300/s
2	20000	60s	300/s
4	40000	59s	650/s
8	80000	54s	1300/s
16	160000	50s	3200/s

Multi-threaded read performance with constant payload size of 100-bytes per operation and fsync enabled.

threads	total-entries	elapsed-time	throughput
1	10000	.15s	66000/s
2	20000	.28s	71000/s
4	40000	.38s	105000/s
8	80000	.62s	130000/s
16	160000	1.10s	150000/s

Contribution

• Simple workflow. Fork - Modify - Pull request.
• Before creating a PR,
  • Run make build to confirm all versions of build is passing with 0 warnings and 0 errors.
  • Run check.sh with 0 warnings, 0 errors and all testcases passing.
  • Run perf.sh with 0 warnings, 0 errors and all testcases passing.
  • Install and run cargo spellcheck to remove common spelling mistakes.
• Developer certificate of origin is preferred.