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https://issues.apache.org/jira/browse/CASSANDRA-1902?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13020171#comment-13020171
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Chris Goffinet edited comment on CASSANDRA-1902 at 4/15/11 3:19 AM:
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CASSANDRA-1470 introduced a way to help not pollute page cache. It also didn't
solve it 100% We realized that during compaction, DONTNEED is used when reading
pages from existing SSTables. While compaction runs this will effectively make
all hot pages in those files, which are still being served be marked to be
removed from cache. So we certainly helped not pollute cache by taking in cold
data, we also effectively removed hot data as well while compaction runs. We
need to modify this patch so that while reading pages on existing SSTables we
be sure to not remove those hot pages during compaction. I am happy to open
another ticket if that makes more sense. But I figured we could just go ahead
and make this ticket support that functionality too.
was (Author: lenn0x):
CASSANDRA-1470 introduced a way to help not pollute page cache. It also
didn't solve it 100% We realized that during compaction, DONTNEED is used when
reading pages from existing SSTables. While compaction runs this will
effectively make all hot pages in those files, which are still being served be
marked to be removed from cache. So we certainly helped not pollute cache, we
also effectively removed hot data as well while compaction runs. We need to
modify this patch so that while reading pages on existing SSTables we be sure
to not remove those hot pages during compaction. I am happy to open another
ticket if that makes more sense. But I figured we could just go ahead and make
this ticket support that functionality too.
> Migrate cached pages during compaction
> ---------------------------------------
>
> Key: CASSANDRA-1902
> URL: https://issues.apache.org/jira/browse/CASSANDRA-1902
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Affects Versions: 0.7.1
> Reporter: T Jake Luciani
> Assignee: Pavel Yaskevich
> Fix For: 1.0
>
> Attachments:
> 0001-CASSANDRA-1902-cache-migration-impl-with-config-option.txt,
> 1902-BufferedSegmentedFile-logandsleep.txt, 1902-formatted.txt,
> 1902-per-column-migration-rebase2.txt, 1902-per-column-migration.txt,
> CASSANDRA-1902-v3.patch, CASSANDRA-1902-v4.patch, CASSANDRA-1902-v5.patch,
> CASSANDRA-1902-v6.patch, CASSANDRA-1902-v7.patch, CASSANDRA-1902-v8.patch,
> CASSANDRA-1902-v9-trunk-rebased.patch,
> CASSANDRA-1902-v9-trunk-with-jmx.patch, CASSANDRA-1902-v9-trunk.patch,
> CASSANDRA-1902-v9.patch
>
> Original Estimate: 32h
> Time Spent: 56h
> Remaining Estimate: 0h
>
> Post CASSANDRA-1470 there is an opportunity to migrate cached pages from a
> pre-compacted CF during the compaction process. This is now important since
> CASSANDRA-1470 caches effectively nothing.
> For example an active CF being compacted hurts reads since nothing is cached
> in the new SSTable.
> The purpose of this ticket then is to make sure SOME data is cached from
> active CFs. This can be done my monitoring which Old SSTables are in the page
> cache and caching active rows in the New SStable.
> A simpler yet similar approach is described here:
> http://insights.oetiker.ch/linux/fadvise/
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