Summary:
Pull Request resolved: https://github.com/facebook/rocksdb/pull/14475
GetLiveFiles was previously blocked on secondary instances with
Status::NotSupported, even though the operation is safe to perform.
The only reason GetLiveFiles was originally blocked is that it defaults
to flushing the memtable (flush_memtable=true), which is a write
operation. However, the actual implementation in DBImpl::GetLiveFiles
(db_filesnapshot.cc) does two things:
1. Optionally flush the memtable — which we skip by passing
flush_memtable=false. The secondary already overrides
FlushForGetLiveFiles() as a no-op, so even if true were passed
it would not actually flush.
2. Read live file state from versions_ under the mutex — this is
purely read-only. It iterates the ColumnFamilySet to collect live
table and blob file numbers, builds relative file paths for SST
files, blob files, CURRENT, MANIFEST, and OPTIONS, and reads the
manifest file size.
The secondary maintains its own VersionSet which it keeps up to date
via MANIFEST replay in TryCatchUpWithPrimary(). So all of this state
is valid and accurate — it reflects exactly which files the secondary
considers live at its current replay point.
This is the same approach used by DBImplReadOnly and CompactedDBImpl,
which both delegate to DBImpl::GetLiveFiles with flush_memtable=false.
Reviewed By: xingbowang
Differential Revision: D97563143
fbshipit-source-id: 8d5b52e26a478ef190eba598819de6527817bcfc
89e384ca6f