Summary:
MyRocks reported some perfomance issues when inserting many keys into a transaction due to the cost of inserting new keys into WriteBatchWithIndex. Frequently, they don't even need the keys to be indexed as they don't need to read them back. DisableIndexing() can be used to avoid the cost of indexing.
I also plan on eventually investigating if we can improve WriteBatchWithIndex performance. But even if we improved the perf here, it is still beneficial to be able to disable the indexing all together for large transactions.
Test Plan: unit test
Reviewers: igor, rven, yoshinorim, spetrunia, sdong
Reviewed By: sdong
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D48471
c5f3707d42