Zhihong Ted Yu created HBASE-6351:
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Summary: IO impact reduction for compaction
Key: HBASE-6351
URL: https://issues.apache.org/jira/browse/HBASE-6351
Project: HBase
Issue Type: Bug
Reporter: Zhihong Ted Yu
Lucene 4.0.0-Alpha was recently released. Mike McCandless, sne of the Lucene
developers, wrote a really nice post about new things in this version of
Lucene. The part that I think is interesting for HBase, and that HBase devs
may want to look at (and borrow to use with compactions) is this:
Reducing merge IO impact
Merging (consolidating many small segments into a single big one) is a very IO
and CPU intensive operation which can easily interfere with ongoing searches.
In 4.0.0 we now have two ways to reduct this impact:
* Rate-limit the IO caused by ongoing merging, by
callingFSDirectory.setMaxMergeWriteMBPerSec.
* Use the new NativeUnixDirectory which bypasses the OS's IO cache for
all merge IO, by using direct IO. This ensures that a merge won't evict hot
pages used by searches. (Note that there is also a native WindowsDirectory, but
it does not yet use direct IO during merging... patches welcome!).
Remember to also set swappiness to 0 on Linux if you want to maximize search
responsiveness.
More generally, the APIs that open an input or output file (Directory.openInput
andDirectory.createOutput) now take an IOContext describing what's being done
(e.g., flush vs merge), so you can create a custom Directory that changes its
behavior depending on the context.
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