Summary:
The max batch size that we can write to the WAL is controlled by a static manner. So if the leader write is less than 128 KB we will have the batch size as leader write size + 128 KB else the limit will be 1 MB. Both of them are statically defined.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5759

Differential Revision: D17329298

fbshipit-source-id: a3d910629d8d8ca84ea39ad89c2b2d284571ded5