[Feature Required] Compaction read/write speed limit

Original [issue 168](https://code.google.com/p/leveldb/issues/detail?id=168) created by wuzuyang on 2013-05-14T03:52:30.000Z:

We are running SSDB(a leveldb server, https://github.com/ideawu/ssdb), with 28G data total, 400k updates per day. LevelDB compaction happends 6-10 times per day. While compaction is in progress, all reads and writes made to leveldb is significant slow. The disk IO is almost full, this is the reason(I think) why leveldb slows down.

What is the expected output? What do you see instead?

Compaction won't slow down normal operations, leveldb's compaction thread should limit the disk read/write speed.

What version of the product are you using? On what operating system?

1.9.0

Please provide any additional information below.