Hi,
Here is something that may be of interest to HBase:
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.
These changes were part of a 2011 Google Summer of Code project (thank you
Varun!).
Thoughts?
Otis
----
Performance Monitoring for Solr / ElasticSearch / HBase -
http://sematext.com/spm
