Summary:
Existing multiGet() in java calls multi_get_helper() which then calls DB::std::vector MultiGet(). This doesn't take advantage of io_uring.
This change adds another JNI level method that runs a parallel code path using the DB::void MultiGet(), using ByteBuffers at the JNI level. We call it multiGetDirect(). In addition to using the io_uring path, this code internally returns pinned slices which we can copy out of into our direct byte buffers; this should reduce the overall number of copies in the code path to/from Java. Some jmh benchmark runs (100k keys, 1000 key multiGet) suggest that for value sizes > 1k, we see about a 20% performance improvement, although performance is slightly reduced for small value sizes, there's a little bit more overhead in the JNI methods.
Closes https://github.com/facebook/rocksdb/issues/8407
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9224
Reviewed By: mrambacher
Differential Revision: D32951754
Pulled By: jay-zhuang
fbshipit-source-id: 1f70df7334be2b6c42a9c8f92725f67c71631690
c1ec0b28eb