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From "Pavel Yaskevich (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-1902) Migrate cached pages during compaction
Date Wed, 06 Apr 2011 13:37:05 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-1902?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13016370#comment-13016370
] 

Pavel Yaskevich commented on CASSANDRA-1902:
--------------------------------------------

My results comparing OLD and NEW (with migration enabled) (rackspace server with 2GB ram the
same as in prev. comments):

script (stress.java) I run (while last compaction goes I run "-n 100000 -o read" in the separate
terminal)

{noformat}
./bin/stress -n 100000 -S 1024 -c 10
sleep 50
./bin/stress -n 100000 -S 1024 -c 10 -o read
./bin/stress -n 100000 -S 1024 -c 10 -o read
./bin/stress -n 100000 -S 1024 -c 10
../../bin/nodetool -h localhost flush Keyspace1 Standard1
echo "start reading"
../../bin/nodetool -h localhost compact Keyspace1 Standard1
{noformat}

Results (OLD | NEW):
{noformat}
191 | 182 (write)
22  | 22  (read)
16  | 16  (read)
184 | 182 (write)
171 | 176 (reads during compaction)
55  | 39  (read after compaction was finished)
{noformat}

I don't post results for new code with migration turned off because it shows the same results
as OLD code except last read after compaction shows improvement - 44 vs 55.


> 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: 0.7.5, 0.8
>
>         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
>
>   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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