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Migrating from InnoDB and HBase to MyRocks at Facebook

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Facebook created a new storage engine called MyRocks to optimize space and write performance, and recently migrated both UDB (a database for social activities, and our biggest in production) and Facebook Messenger to MyRocks. In this session, Yoshinori Matsunobu of Facebook talks about the challenges, benefits and lessons learned by migrating these applications from InnoDB to MyRocks.

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Migrating from InnoDB and HBase to MyRocks at Facebook

  1. 1. Migrating InnoDB and HBase to MyRocks Yoshinori Matsunobu Production Engineer / MySQL Tech Lead, Facebook Feb 2019, MariaDB Openworks
  2. 2. What is MyRocks ▪ MySQL on top of RocksDB (Log-Structured Merge Tree Database) ▪ Open Source, distributed from MariaDB and Percona as well MySQL Clients InnoDB RocksDB Parser Optimizer Replication etc SQL/Connector MySQL http://myrocks.io/
  3. 3. LSM Compaction Algorithm -- Level ▪ For each level, data is sorted by key ▪ Read Amplification: 1 ~ number of levels (depending on cache -- L0~L3 are usually cached) ▪ Write Amplification: 1 + 1 + fanout * (number of levels – 2) / 2 ▪ Space Amplification: 1.11 ▪ 11% is much smaller than B+Tree’s fragmentation
  4. 4. bottommost_compression and compression_per_level compression_per_level=kLZ4Compression or kNoCompression bottommost_compression=kZSTD ▪ Use stronger compression algorithm (Zstandard) in Lmax to save space ▪ Use faster compression algorithm (LZ4 or None) in higher levels to keep up with writes
  5. 5. Read, Write and Space Performance/Efficiency ▪ Pick two of them ▪ InnoDB/B-Tree favors Read at cost of Write and Space ▪ For large scale database on Flash, Space is important ▪ Read inefficiency can be mitigated by Flash and Cache tiers ▪ Write inefficiency can not be easily resolved ▪ Implementations matter (e.g. ZSTD > Zlib)
  6. 6. Read, Write and Space Performance/Efficiency - Compressed InnoDB is roughly 2x smaller than uncompressed InnoDB, MyRocks/HBase are 4x smaller - Decompression cost on read is non zero. It matters less on i/o bound workloads - HBase vs MyRocks perf differences came from implementation efficiencies rather than database architecture
  7. 7. UDB – Migration from InnoDB to MyRocks ▪ UDB: Our largest user database that stores social activities ▪ Biggest motivation was saving space ▪ 2X savings vs compressed InnoDB, 4X vs uncompressed InnoDB ▪ Write efficiency was 10X better ▪ Read efficiency was no worse than X times ▪ Could migrate without rewriting applications
  8. 8. User Database at Facebook InnoDB in user database 90% SpaceIOCPU Machine limit 15%20% MyRocks in user database 45% SpaceIOCPU Machine limit 15%21% 21% 15% 45%
  9. 9. MyRocks on Facebook Messaging ▪ In 2010, we created Facebook Messenger and we chose HBase as backend database ▪ LSM database ▪ Write optimized ▪ Smaller space ▪ Good enough on HDD ▪ Successful MyRocks on UDB led us to migrate Messenger as well ▪ MyRocks used much less CPU time, worked well on Flash ▪ p95~99 latency and error rates improved by 10X ▪ Migrated from HBase to MyRocks in 2017~2018
  10. 10. FB Messaging Migration from HBase to MyRocks
  11. 11. MyRocks migration -- Technical Challenges ▪ Migration ▪ Creating MyRocks instances without downtime ▪ Loading into MyRocks tables within reasonable time ▪ Verifying data consistency between InnoDB and MyRocks ▪ Serving write traffics ▪ Continuous Monitoring ▪ Resource Usage like space, iops, cpu and memory ▪ Query plan outliers ▪ Stalls and crashes
  12. 12. Creating first MyRocks instance without downtime ▪ Picking one of the InnoDB slave instances, then starting logical dump and restore ▪ Stopping one slave does not affect services Master (InnoDB) Slave1 (InnoDB) Slave2 (InnoDB) Slave3 (InnoDB) Slave4 (MyRocks) Stop & Dump & Load
  13. 13. Faster Data Loading Normal Write Path in MyRocks/RocksDB Write Requests MemTableWAL Level 0 SST Level 1 SST Level max SST …. Flush Compaction Compaction Faster Write Path Write Requests Level max SST
  14. 14. Creating second MyRocks instance without downtime Master (InnoDB) Slave1 (InnoDB) Slave2 (InnoDB) Slave3 (MyRocks) Slave4 (MyRocks) myrocks_hotbackup (Online binary backup)
  15. 15. Shadow traffic tests ▪ We have a shadow test framework ▪ MySQL audit plugin to capture read/write queries from production instances ▪ Replaying them into shadow master instances ▪ Shadow master tests ▪ Client errors ▪ Rewriting queries relying on Gap Lock ▪ Added a feature to detect such queries
  16. 16. Promoting MyRocks as a master Master (MyRocks) Slave1 (InnoDB) Slave2 (InnoDB) Slave3 (InnoDB) Slave4 (MyRocks)
  17. 17. Promoting MyRocks as a master Master (MyRocks) Slave1 (MyRocks) Slave2 (MyRocks) Slave3 (MyRocks) Slave4 (MyRocks)
  18. 18. Improvements after migration
  19. 19. Switching to Direct I/O ▪ MyRocks/RocksDB relied on Buffered I/O while InnoDB had Direct I/O ▪ Heavily dependent on Linux Kernel ▪ Stalls often happened on older Linux Kernel ▪ Wasted memory for slab (10GB+ DRAM was not uncommon) ▪ Swap happened under memory pressure
  20. 20. Direct I/O configurations in MyRocks/RocksDB ▪ rocksdb_use_direct_reads = ON ▪ rocksdb_use_direct_io_for_flush_and_compaction = ON ▪ rocksdb_cache_high_pri_pool_ratio = 0.5 ▪ Avoiding invalidating caches on ad hoc full table scan ▪ SET GLOBAL rocksdb_block_cache_size = X ▪ Dynamically changing buf pool size online, without causing stalls
  21. 21. Bulk loading Secondary Keys ▪ ALTER TABLE … ADD INDEX secondary_key (…) ▪ This enters bulk loading path for building a secondary key ▪ A big pain point for us was it blocked live master promotion ▪ (orig master) SET GLOBAL read_only=1; (new master) CHANGE MASTER; read_only=0; ▪ ALTER TABLE blocks SET GLOBAL read_only=1 ▪ Nonblocking bulk loading ▪ CREATE TABLE with primary and secondary keys; ▪ SET SESSION rocksdb_bulk_load_allow_sk=1; ▪ SET SESSION rocksdb_bulk_load=1; ▪ LOAD DATA ….. (bulk loading into primary key, and creating temporary files for secondary keys) ▪ SET SESSION rocksdb_bulk_load=0; // building secondary keys without blocking read_only=1
  22. 22. Zstandard dictionary compression ▪ Dictionary helps to save space and decompression speed, especially for small blocks ▪ Dictionary is created for each SST file ▪ Newer Zstandard (1.3.6+) has significant improvements for creating dictionaries ▪ max_dict_bytes (8KB) and zstd_max_train_bytes (256KB) -- compression_opts=- 14:6:0:8192:262144
  23. 23. Parallel and reliable Manual Compaction ▪ Several configuration changes need reformatting data to get benefits ▪ Changing compression algorithm or compression level ▪ Changing bloom filter settings ▪ Changing block size ▪ Parallel Manual Compaction is useful to reformat quickly ▪ set session rocksdb_manual_compaction_threads=24; ▪ set global rocksdb_compact_cf=‘default’; ▪ (Manual Compaction is done for a specified CF) ▪ Not blocking DDL, DML, Replication
  24. 24. compaction_pri=kMinOverlappingRatio ▪ Default compaction priority (kByCompensatedSize) picks SST files that have many deletions ▪ In general, it reads and writes more than necessary ▪ compaction_pri=kMinOverlappingRatio compacts files that overlap less between levels ▪ Typically reducing read/write bytes and compaction time spent by half
  25. 25. Controlling compaction volume and speed ▪ From performance stability point of view: ▪ Each compaction should not run too long ▪ Should not generate new SST files too fast ▪ On Flash, should not remove old SST files too fast ▪ max_compaction_bytes=400MB ▪ rocksdb_sst_mgr_rate_bytes_per_sec = 64MB ▪ rocksdb_delete_obsolete_files_period_micros = 64MB ▪ rocksdb_max_background_jobs = 12 ▪ Compactions start with one thread, and gradually increasing threads based on pending compaction bytes
  26. 26. TTL based compactions ▪ When database size becomes large, you may run some logical-deletion jobs to purge old data ▪ But old Lmax SST files might not be deleted as expected, higher levels have old SST files remained. As a result, space is not reclaimed ▪ TTL based compaction forces to compact old SST files in higher levels, to make sure to reclaim space L1 L2 L3 key=1, value=1MB Key=2, value=1MB … Key=1, value=null Key=2, value=null L1 L2 L3 key=1, value=null Key=2, value=null …
  27. 27. Read Free Replication ▪ Read Free Replication is a feature to skip random reads on replicas ▪ Skipping unique constraint checking on INSERT (slave) ▪ Skipping finding rows on UPDATE/DELETE (slave) ▪ (Upcoming) Skipping both on REPLACE (master/slave) ▪ rocksdb-read-free-rpl = OFF, PK_ONLY, PK_SK ▪ Enabling Read Free for INSERT, UPDATE and DELETE for tables, depending on secondary keys existence ▪ If you update outside of replication, secondary indexes may become inconsistent
  28. 28. Dynamic Options ▪ Most DB and CF options can now be changed online ▪ Example Command ▪ SET @@global.rocksdb_update_cf_options = 'cf1={write_buffer_size=8m;target_file_size_base=2m};cf2={write_buffer_size=16m;max_byte s_for_level_multiplier=8};cf3={target_file_size_base=4m};'; ▪ Can be viewed new CF setting from information_schema ▪ SELECT * FROM ROCKSDB_CF_OPTIONS WHERE CF_NAME='cf1' AND OPTION_TYPE='WRITE_BUFFER_SIZE'; ▪ SELECT * FROM ROCKSDB_CF_OPTIONS WHERE CF_NAME='cf1' AND OPTION_TYPE='TARGET_FILE_SIZE_BAS'; ▪ Values are not persisted. You need to update my.cnf to get persisted
  29. 29. Our current status ▪ Our two biggest database services (UDB and Facebook Messenger) have been reliably running on top of MyRocks ▪ Efficiency wins : InnoDB to MyRocks ▪ Performance and Reliability wins : HBase to MyRocks ▪ Gradually working on migrating long tail, smaller database services to MyRocks
  30. 30. Future Plans ▪ MySQL 8.0 ▪ Pushing more efficiency efforts ▪ Simple read query paths to be much more CPU efficient ▪ Working without WAL, engine crash recovery relying on Binlog ▪ Towards more general purpose database ▪ Gap Lock and Foreign Key ▪ Long running transactions ▪ Online and fast schema changes ▪ Mixing MyRocks and InnoDB in the same instance
  31. 31. (c) 2009 Facebook, Inc. or its licensors. "Facebook" is a registered trademark of Facebook, Inc.. All rights reserved. 1.0

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