Summary:
Previously each time we write a blob we write blog_record_header + key + value + blob_record_footer to blob log. The footer only contains a sequence and a crc for the sequence number. The sequence number was used in garbage collection to verify the value is recent. After #2703 we moved to use optimistic transaction and no longer use sequence number from the footer. Remove the footer altogether.
There's another usage of sequence number and we are keeping it: Each blob log file keep track of sequence number range of keys in it, and use it to check if it is reference by a snapshot, before being deleted.
Closes https://github.com/facebook/rocksdb/pull/3005
Differential Revision: D6057585
Pulled By: yiwu-arbug
fbshipit-source-id: d6da53c457a316e9723f359a1b47facfc3ffe090
Summary:
While GC, blob DB use optimistic transaction to delete or replace the index entry in LSM, to guarantee correctness if there's a normal write writing to the same key. However, the previous implementation doesn't call SetSnapshot() nor use GetForUpdate() of transaction API, instead it do its own sequence number checking before beginning the transaction. A normal write can sneak in after the sequence number check and overwrite the key, and the GC will delete or relocate the old version of the key by mistake. Update the code to property use GetForUpdate() to check the existing index entry.
After the patch the sequence number store with each blob record is useless, So I'm considering remove the sequence number from blob record, in another patch.
Closes https://github.com/facebook/rocksdb/pull/2703
Differential Revision: D5589178
Pulled By: yiwu-arbug
fbshipit-source-id: 8dc960cd5f4e61b36024ba7c32d05584ce149c24
