Summary:
In the past, we unnecessarily requires all keys in the same write batch
to be from column families whose timestamps' formats are the same for
simplicity. Specifically, we cannot use the same write batch to write to
two column families, one of which enables timestamp while the other
disables it.
The limitation is due to the member `timestamp_size_` that used to exist
in each `WriteBatch` object. We pass a timestamp_size to the constructor
of `WriteBatch`. Therefore, users can simply use the old
`WriteBatch::Put()`, `WriteBatch::Delete()`, etc APIs for write, while
the internal implementation of `WriteBatch` will take care of memory
allocation for timestamps.
The above is not necessary.
One the one hand, users can set up a memory buffer to store user key and
then contiguously append the timestamp to the user key. Then the user
can pass this buffer to the `WriteBatch::Put(Slice&)` API.
On the other hand, users can set up a SliceParts object which is an
array of Slices and let the last Slice to point to the memory buffer
storing timestamp. Then the user can pass the SliceParts object to the
`WriteBatch::Put(SliceParts&)` API.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/8725
Test Plan: make check
Reviewed By: ltamasi
Differential Revision: D30654499
Pulled By: riversand963
fbshipit-source-id: 9d848c77ad3c9dd629aa5fc4e2bc16fb0687b4a2
2a2b3e03a5