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https://issues.apache.org/jira/browse/CASSANDRA-1902?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13012511#comment-13012511
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Jonathan Ellis commented on CASSANDRA-1902:
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bq. NormalMappedSegment is used in cases when we don't have a page size (JNA is
not installed or not on Linux)
Makes sense.
bq. using NativeMappedSegment we don't need to duplicate buffers on slice calls
Don't we still need to duplicate, in case we unmap the sstable we read from
before we return the data to the requester?
Similarly, if we manually munmap, isn't there a race condition where we say
"give me the list of sstables" and then while reading one gets compacted and
unmapped?
> 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: T Jake Luciani
> Fix For: 0.7.5, 0.8
>
> Attachments:
> 0001-CASSANDRA-1902-cache-migration-impl-with-config-option.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
>
> 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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