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https://issues.apache.org/jira/browse/CASSANDRA-1902?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12996215#comment-12996215
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Jonathan Ellis commented on CASSANDRA-1902:
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bq. 32 * 4k isn't a large value
It's huge for "object data" CFs (vs "materialized view" CFs).
For comparison, postgresql default block size is 8K and you typically have
several if not dozens of rows in a single block.
bq. I guess we could base it on some fraction of the avg row size per CF?
That would be a brute force solution but you come back to fairly large overhead
to track it all at once. Lazy computation really seems better to me.
> 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: 0.7.3
>
> Attachments:
> 0001-CASSANDRA-1902-cache-migration-impl-with-config-option.txt,
> 1902-formatted.txt
>
> Original Estimate: 32h
> Time Spent: 24h
> Remaining Estimate: 8h
>
> Post CASSANDRA-1470 there is an opportunity to migrate cached pages from a
> pre-compacted CF during the compaction process.
> First, add a method to MmappedSegmentFile: long[] pagesInPageCache() that
> uses the posix mincore() function to detect the offsets of pages for this
> file currently in page cache.
> Then add getActiveKeys() which uses underlying pagesInPageCache() to get the
> keys actually in the page cache.
> use getActiveKeys() to detect which SSTables being compacted are in the os
> cache and make sure the subsequent pages in the new compacted SSTable are
> kept in the page cache for these keys. This will minimize the impact of
> compacting a "hot" SSTable.
> A simpler yet similar approach is described here:
> http://insights.oetiker.ch/linux/fadvise/
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