As Himanshu points out in the the parent issue, HLogPE is using an unorthodox API appending edits to the WAL; it is using an API that is meant for tests only that does an append immediately followed by a sync call.
In normal deploy, WAL appends are done as a bunch of appends followed by a sync on the tail of the transaction – not a sync per append.
This issue is about changing HLogPE to use append and then sync. It also adds an argument so you can specifying batching of a set of appends before the sync is called. The latter lets HLogPE mimic multi puts that use the minibatch... which appends, appends, appends.. and then syncs.
Assigning to Himanshu for review.