[PATCH] vinyl: fix compaction vs checkpoint race resulting in invalid gc

[Konstantin Osipov]

* Vladimir Davydov <vdavydov.dev at gmail.com> [18/05/31 15:51]:
> The callback invoked upon compaction completion uses checkpoint_last()
> to determine whether compacted runs may be deleted: if the max LSN
> stored in a compacted run (run->dump_lsn) is greater than the LSN of the
> last checkpoint (gc_lsn) then the run doesn't belong to the last
> checkpoint and hence is safe to delete, see commit 35db70fac55c ("vinyl:
> remove runs not referenced by any checkpoint immediately").
> 
> The problem is checkpoint_last() isn't synced with vylog rotation - it
> returns the signature of the last successfully created memtx snapshot
> and is updated in memtx_engine_commit_checkpoint() after vylog is
> rotated. If a compaction task completes after vylog is rotated but
> before snap file is renamed, it will assume that compacted runs do not
> belong to the last checkpoint, although they do (as they have been
> appended to the rotated vylog), and delete them.
> 
> To eliminate this race, let's use vylog signature instead of snap
> signature in vy_task_compact_complete().
> 
> Closes #3437


Pushed.

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Konstantin Osipov, Moscow, Russia, +7 903 626 22 32
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