Summary:
`Compaction` is already creating its own ref for the input Version: 4b1d595306/db/compaction/compaction.cc (L73)
And properly Unref it during destruction:
4b1d595306/db/compaction/compaction.cc (L450)
This PR redirects compaction's access of `cfd->current()` to this input `Version`, to prepare for when a column family's data can be replaced all together, and `cfd->current()` is not safe to access for a compaction job. Because a new `Version` with just some other external files could be installed as `cfd->current()`. The compaction job's expectation of the current `Version` and the corresponding storage info to always have its input files will no longer be guaranteed.
My next follow up is to do a similar thing for flush, also to prepare it for when a column family's data can be replaced. I will make it create its own reference of the current `MemTableListVersion` and use it as input, all flush job's access of memtables will be wired to that input `MemTableListVersion`. Similarly this reference will be unreffed during a flush job's destruction.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/12992
Test Plan: Existing tests
Reviewed By: pdillinger
Differential Revision: D62212625
Pulled By: jowlyzhang
fbshipit-source-id: 9a781213469cf366857a128d50a702af683a046a
RocksDB: A Persistent Key-Value Store for Flash and RAM Storage
RocksDB is developed and maintained by Facebook Database Engineering Team.
It is built on earlier work on LevelDB by Sanjay Ghemawat (sanjay@google.com)
and Jeff Dean (jeff@google.com)
This code is a library that forms the core building block for a fast
key-value server, especially suited for storing data on flash drives.
It has a Log-Structured-Merge-Database (LSM) design with flexible tradeoffs
between Write-Amplification-Factor (WAF), Read-Amplification-Factor (RAF)
and Space-Amplification-Factor (SAF). It has multi-threaded compactions,
making it especially suitable for storing multiple terabytes of data in a
single database.
The public interface is in include/. Callers should not include or
rely on the details of any other header files in this package. Those
internal APIs may be changed without warning.
RocksDB is dual-licensed under both the GPLv2 (found in the COPYING file in the root directory) and Apache 2.0 License (found in the LICENSE.Apache file in the root directory). You may select, at your option, one of the above-listed licenses.
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