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Date: Thu, 5 Jul 2012 18:16:35 +0000 (UTC)
From: "Jean-Daniel Cryans (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
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Subject: [jira] [Commented] (HBASE-6312) Make BlockCache eviction thresholds
 configurable
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    [ https://issues.apache.org/jira/browse/HBASE-6312?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13407348#comment-13407348 ] 

Jean-Daniel Cryans commented on HBASE-6312:
-------------------------------------------

bq. According to your suggestion, shall we need to make that gap (between the minimum and acceptable factor) configurable at least?

We can, I just don't know how useful that's gonna be. It can hardly be worse than it is right now tho :)

bq. Maybe We should evict only after cache size is large than hfile.block.cache.size, and allow ~15% burstiness before blocking.

It seems to me that we'd just have the reverse problem.

The real problem here is that LruBlockCache won't let us use exactly the amount of memory we want, it's like driving a car and the best you can do is steering all the way left or all the way right because keeping it centered would require too much effort.

Right now I'd be in favor of setting the acceptable factor to 99% and the minimum at 95% since it's really hard to overflow and there's no blocking. We can make the minimum configurable so that if someone sees that it's evicting too often they can tune it down.
                
> Make BlockCache eviction thresholds configurable
> ------------------------------------------------
>
>                 Key: HBASE-6312
>                 URL: https://issues.apache.org/jira/browse/HBASE-6312
>             Project: HBase
>          Issue Type: Improvement
>          Components: io
>    Affects Versions: 0.94.0
>            Reporter: Jie Huang
>            Priority: Minor
>         Attachments: hbase-6312.patch
>
>
> Some of our customers found that tuning the BlockCache eviction thresholds made test results different in their test environment. However, those thresholds are not configurable in the current implementation. The only way to change those values is to re-compile the HBase source code. We wonder if it is possible to make them configurable.

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