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From "Chris Burroughs (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-6574) key cache shrinks on restart
Date Fri, 20 Nov 2015 14:59:11 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-6574?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15018118#comment-15018118
] 

Chris Burroughs commented on CASSANDRA-6574:
--------------------------------------------

Current Status:
 * All of the stuff about wild fluctuations in hit rate is CASSANDRA-6591
 * There have been a bunch of fixes to key-cache loading since this ticket was opened, maybe
this was fixed incidentally?
 * My largest cluster is now longer has anything with the key cache enabled so I don't have
a great sample size for checking.

My inclinations is to (if writing this comment implying everything might be fixed doesn't
curse me with problems) clean up the logging a bit  ("harmless" does not feel like the right
word for "this node is about to join the cluster but performance may be be terrible") but
otherwise this can be wound down.

> key cache shrinks on restart
> ----------------------------
>
>                 Key: CASSANDRA-6574
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6574
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Local Write-Read Paths
>         Environment: 1.2.12 + patches
>            Reporter: Chris Burroughs
>            Priority: Minor
>             Fix For: 3.x
>
>         Attachments: key-cache-entries.png, key-cache-rate.png, key-cache.png
>
>
> During a rolling restart the key number of entries the number of entries in the key cache
is shrinking.  That is far fewer entries are loaded than are saved.  This has obvious bad
consequences for post restart performance.
> {noformat}
> key_cache_size_in_mb: 48
> key_cache_save_period: 900
> # Number of keys from the key cache to save
> # Disabled by default, meaning all keys are going to be saved
> # key_cache_keys_to_save: 100
> row_cache_size_in_mb: 256
> row_cache_save_period: 300
> row_cache_keys_to_save: 50000
> row_cache_provider: SerializingCacheProvider
> saved_caches_directory: /home/cassandra/shared/saved_caches
> {noformat}
> Same log lines:
> {noformat}
>  INFO [CompactionExecutor:24543] 2014-01-11 11:35:47,783 AutoSavingCache.java (line 289)
Saved KeyCache (398028 items) in 1252 ms
> *** RESTART ***
>  INFO [main] 2014-01-11 11:44:59,608 AutoSavingCache.java (line 140) reading saved cache
/home/cassandra/shared/saved_caches/ks-cf1-KeyCache-b.db
>  INFO [main] 2014-01-11 11:45:00,509 AutoSavingCache.java (line 140) reading saved cache
/home/cassandra/shared/saved_caches/ks-cf2-RowCache-b.db
>  INFO [main] 2014-01-11 12:02:48,675 ColumnFamilyStore.java (line 452) completed loading
(1068166 ms; 50000 keys) row cache for ks.cf2
>  INFO [main] 2014-01-11 12:02:48,769 CassandraDaemon.java (line 291) completed pre-loading
(67760 keys) key cache.
>  INFO [main] 2014-01-11 12:02:48,769 CassandraDaemon.java (line 294) completed pre-loading
(50000 keys) row cache.
>  INFO [CompactionExecutor:1] 2014-01-11 12:02:49,133 AutoSavingCache.java (line 289)
Saved RowCache (50000 items) in 266 ms
>  INFO [CompactionExecutor:2] 2014-01-11 12:02:49,575 AutoSavingCache.java (line 289)
Saved KeyCache (67760 items) in 707 ms
> {noformat}



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