Summary:
https://github.com/facebook/rocksdb/pull/6531 removed some code in partitioned index seek logic. By mistake the logic of storing previous index offset is removed, while the logic of using it is preserved, so that the code might use wrong value to determine reseeking condition.
This will trigger a bug, if following a Seek() not going to the last block, SeekToLast() is called, and then Seek() is called which should position the cursor to the block before SeekToLast().
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6551
Test Plan: Add a unit test that reproduces the bug. In the same unit test, also some reseek cases are covered to avoid regression.
Reviewed By: pdillinger
Differential Revision: D20493990
fbshipit-source-id: 3919aa4861c0481ec96844e053048da1a934b91d