[jira] [Comment Edited] (HBASE-14404) Backport HBASE-14098 (Allow dropping caches behind compactions) to 0.98

["Andrew Purtell (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-14404?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14876786#comment-14876786 ] 

Andrew Purtell edited comment on HBASE-14404 at 9/19/15 1:18 AM:
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As a backport issue we are carrying back a change from later branches that alters reader and writer behavior unconditionally. I can make it conditional upon HBase settings changes (falling back to the HDFS level settings for dropping behind reads and writes, or simply not changing anything if our config doesn't say) but can't use the backport in that case. It has to be a different approach that looks at configuration where we set up the readers and writers, rather than once in CacheConfig. Would no longer be a backport, but instead something unique to 0.98. I don't think that's what we want. Since I have a +1 to commit the earlier patch I'm going to drop the half-assed thing I put up a few minutes ago and commit the original backport patch shortly.


was (Author: apurtell):
As a backport issue we are carrying back a change from later branches that alter reader and writer behavior unconditionally. I can make it conditional upon HBase settings changes but can't use the backport. It has to be a different approach that looks at configuration where we set up the readers and writers, rather than once in CacheConfig. Would no longer be a backport, but instead something unique to 0.98. I don't think that's what we want. Since I have a +1 to commit the earlier patch I'm going to drop the half-assed thing I put up a few minutes ago and commit the original backport patch shortly.

> Backport HBASE-14098 (Allow dropping caches behind compactions) to 0.98
> -----------------------------------------------------------------------
>
>                 Key: HBASE-14404
>                 URL: https://issues.apache.org/jira/browse/HBASE-14404
>             Project: HBase
>          Issue Type: Task
>            Reporter: Andrew Purtell
>            Assignee: Andrew Purtell
>             Fix For: 0.98.15
>
>         Attachments: HBASE-14404-0.98.patch
>
>
> HBASE-14098 adds a new configuration toggle - "hbase.hfile.drop.behind.compaction" - which if set to "true" tells compactions to drop pages from the OS blockcache after write.  It's on by default where committed so far but a backport to 0.98 would default it to off. (The backport would also retain compat methods to LimitedPrivate interface StoreFileScanner.) What could make it a controversial change in 0.98 is it changes the default setting of 'hbase.regionserver.compaction.private.readers' from "false" to "true".  I think it's fine, we use private readers in production. They're stable and do not present perf issues.



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