Hui Xiao d985902ef4 Disallow refitting more than 1 file from non-L0 to L0 (#12481) ... Summary: **Context/Summary:** We recently discovered that `CompactRange(change_level=true, target_level=0)` can possibly refit more than 1 files to L0. This refitting can cause read performance regression as we need to go through every file in L0, corruption in some edge case and false positive corruption caught by force consistency check. We decided to explicitly disallow such behavior. A related change to OptionChangeMigration(): - When migrating to FIFO with `compaction_options_fifo.max_table_files_size > 0`, RocksDB will [CompactRange() all the to-be-migrate data into a couple L0 files](https://github.com/facebook/rocksdb/blob/main/utilities/option_change_migration/option_change_migration.cc#L164-L169) to avoid dropping all the data upon migration finishes when the migrated data is larger than max_table_files_size. This is achieved by first compacting all the data into a couple non-L0 files and refitting those files from non-L0 to L0 if needed. In that way, only some data instead of all data will be dropped immediately after migration to FIFO with a max_table_files_size. - Since this type of refitting behavior is disallowed from now on, we won't do this trick anymore and explicitly state such risk in API comment. Pull Request resolved: https://github.com/facebook/rocksdb/pull/12481 Test Plan: - New UT - Modified UT Reviewed By: cbi42 Differential Revision: D55351178 Pulled By: hx235 fbshipit-source-id: 9d8854f2f81d7e8aff859c3a4e53b7d688048e80		2024-03-29 10:52:36 -07:00
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migrate_fifo.md	Disallow refitting more than 1 file from non-L0 to L0 (#12481)	2024-03-29 10:52:36 -07:00