mirror of https://github.com/facebook/rocksdb.git
26b480609c
Summary: This PR adds support for reusing the file system provided buffer to avoid an extra `memcpy` into RockDB's buffer. This optimization has already been implemented for point lookups, as well as compaction and scan reads _when prefetching is disabled_. This PR extends this optimization to work with synchronous prefetching (`num_buffers == 1`). Asynchronous prefetching can be addressed in a future PR (and probably should be to keep this PR from growing too large). Remarks - To handle the case where the main buffer only has part of the requested data, I used the existing `overlap_buf_` (currently used in the async prefetching case) instead of defining a separate buffer. This was discussed in https://github.com/facebook/rocksdb/pull/13118#discussion_r1842839360. - We use `MultiRead` with a single request to take advantage of the file system buffer. This is consistent with previous work (e.g. https://github.com/facebook/rocksdb/pull/12266). - Even without the tests I added, there was some code coverage inside in at least `DBIOCorruptionTest.IterReadCorruptionRetry`, since those tests were failing before I addressed a bug in my code for this PR. [Run with failed test](https://github.com/facebook/rocksdb/actions/runs/11708830448/job/32611508818?pr=13118). - This prefetching code is not too easy to follow, so I added quite a bit of comments to both the code and test case to try to make it easier to understand the exact internal state of the prefetch buffer at every point in time. Pull Request resolved: https://github.com/facebook/rocksdb/pull/13118 Test Plan: I wrote pretty thorough unit tests that cover synchronous prefetching with file system buffer reuse. The flows for partial hits, complete hits, and complete misses are tested. I also parametrized the test to make sure the async prefetching (without file system buffer reuse) still work as expected. Once we agree on the changes, I will run a long stress test before merging. Reviewed By: anand1976 Differential Revision: D65559101 Pulled By: archang19 fbshipit-source-id: 1a56d846e918c20a009b83f1371c1791f69849ae |
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