Review Board 1.7.22

HBASE-4608 HLog Compression

Review Request #4185 - Created March 5, 2012 and updated

Ted Yu
The current bottleneck to HBase write speed is replicating the WAL appends across different datanodes. We can speed up this process by compressing the HLog. Current plan involves using a dictionary to compress table name, region id, cf name, and possibly other bits of repeated data. Also, HLog format may be changed in other ways to produce a smaller HLog.
New unit tests are added and pass.
Review request changed
Updated (March 12, 2012, 9:57 p.m.)
Renamed enableCompression()

To be done: introducing WAL version metadata and adding more tests to TestLRUDictionary