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
0c6e9c036a