Provide byte[] version of SstFileWriter.merge to reduce GC Stall
Summary:
In Java API, `SstFileWriter.put/merge/delete` takes `Slice` type of key and value, which is a Java wrapper object around C++ Slice object. The Slice object inherited [ `finalize`](3c327ac2d0/java/src/main/java/org/rocksdb/AbstractNativeReference.java (L69)) method, which [added huge overhead](https://softwareengineering.stackexchange.com/questions/288715/is-overriding-object-finalize-really-bad/288753#288753) to JVM while creating new SstFile.
To address this issue, this PR overload the merge method to take Java byte array instead of the Slice object, and added unit test for it.
We also benchmark these two different merge function, where we could see GC Stall reduced from 50% to 1%, and the throughput increased from 50MB to 200MB.
Closes https://github.com/facebook/rocksdb/pull/2746
Reviewed By: sagar0
Differential Revision: D5653145
Pulled By: scv119
fbshipit-source-id: b55ea58554b573d0b1c6f6170f8d9223811bc4f5
78cb6b6112