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From "Otis Gospodnetic (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HBASE-6351) IO impact reduction for compaction
Date Wed, 11 Jul 2012 19:05:34 GMT

     [ https://issues.apache.org/jira/browse/HBASE-6351?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Otis Gospodnetic updated HBASE-6351:
------------------------------------

    Description: 
The following came from Otis via http://search-hadoop.com/m/MGVqgZJ4Mj2 :

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 calling FSDirectory.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 and Directory.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. 

  was:
The following came from Otis:

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 calling FSDirectory.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 and Directory.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. 

    
> 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
>
> The following came from Otis via http://search-hadoop.com/m/MGVqgZJ4Mj2 :
> 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 calling FSDirectory.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 and Directory.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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