Summary:
RocksDB's `Cache` abstraction currently supports two priority levels for items: high (used for frequently accessed/highly valuable SST metablocks like index/filter blocks) and low (used for SST data blocks). Blobs are typically lower-value targets for caching than data blocks, since 1) with BlobDB, data blocks containing blob references conceptually form an index structure which has to be consulted before we can read the blob value, and 2) cached blobs represent only a single key-value, while cached data blocks generally contain multiple KVs. Since we would like to make it possible to use the same backing cache for the block cache and the blob cache, it would make sense to add a new, lower-than-low cache priority level (bottom level) for blobs so data blocks are prioritized over them.
This task is a part of https://github.com/facebook/rocksdb/issues/10156
Pull Request resolved: https://github.com/facebook/rocksdb/pull/10309
Reviewed By: ltamasi
Differential Revision: D38211655
Pulled By: gangliao
fbshipit-source-id: 65ef33337db4d85277cc6f9782d67c421ad71dd5
Summary:
**Summary:**
RocksDB uses a block cache to reduce IO and make queries more efficient. The block cache is based on the LRU algorithm (LRUCache) and keeps objects containing uncompressed data, such as Block, ParsedFullFilterBlock etc. It allows the user to configure a second level cache (rocksdb::SecondaryCache) to extend the primary block cache by holding items evicted from it. Some of the major RocksDB users, like MyRocks, use direct IO and would like to use a primary block cache for uncompressed data and a secondary cache for compressed data. The latter allows us to mitigate the loss of the Linux page cache due to direct IO.
This PR includes a concrete implementation of rocksdb::SecondaryCache that integrates with compression libraries such as LZ4 and implements an LRU cache to hold compressed blocks.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9518
Test Plan:
In this PR, the lru_secondary_cache_test.cc includes the following tests:
1. The unit tests for the secondary cache with either compression or no compression, such as basic tests, fails tests.
2. The integration tests with both primary cache and this secondary cache .
**Follow Up:**
1. Statistics (e.g. compression ratio) will be added in another PR.
2. Once this implementation is ready, I will do some shadow testing and benchmarking with UDB to measure the impact.
Reviewed By: anand1976
Differential Revision: D34430930
Pulled By: gitbw95
fbshipit-source-id: 218d78b672a2f914856d8a90ff32f2f5b5043ded
Peter Dillinger