pr#30149 - [luminous] Set concurrent bluestore rocksdb compactions to 2

Mark called out [0] a specific issue [1] in older versions of rocksdb that may cause problems when running multiple concurrent compaction threads. The luminous 12.2.13 rocksdb submodule branch rests somewhere between the following rocksdb tags: tags/v4.9 (960 commits ahead) tags/v5.5.1 (97 commits behind) The concurrency issue was fixed by a commit [2] that landed well after v5.5.1: git describe --contains 4420df4b0e15ae88911e960c4fbafbaf8450fcf7 v5.15.10~154 The fix is present in nautilus, but not in luminous. Am I missing something that mitigates the risk of running concurrent compactions in Luminous? Should this default be reverted back to 1? [0] https://github.com/ceph/ceph/pull/29027#issue-297158998 [1] https://github.com/facebook/rocksdb/pull/3926 [2] https://github.com/facebook/rocksdb/commit/4420df4b0e15ae88911e960c4fbafbaf… Thanks, Dan Hill