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https://issues.apache.org/jira/browse/CASSANDRA-6574?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14637466#comment-14637466
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Chris Burroughs commented on CASSANDRA-6574:
--------------------------------------------

I think the fail safe catch is per saved cache and not per entry, so if there 
is a problem somewhere early in a 29 MiB cache file we could end up loading 
zero keys from it.
{noformat}
DEBUG [main] 2015-07-22 15:05:19,002 AutoSavingCache.java (line 136) harmless 
error reading saved cache 
/home/cassandra/shared/saved_caches/urlapi_v2-DOMData-KeyCache-b.db
java.io.IOException: Corrupted key cache. Key length of 402838960 is longer 
than maximum of 65535
        at 
org.apache.cassandra.service.CacheService$KeyCacheSerializer.deserialize(CacheService.java:353)
        at 
org.apache.cassandra.cache.AutoSavingCache.loadSaved(AutoSavingCache.java:119)
        at 
org.apache.cassandra.db.ColumnFamilyStore.<init>(ColumnFamilyStore.java:263)
        at 
org.apache.cassandra.db.ColumnFamilyStore.createColumnFamilyStore(ColumnFamilyStore.java:422)
        at 
org.apache.cassandra.db.ColumnFamilyStore.createColumnFamilyStore(ColumnFamilyStore.java:393)
        at org.apache.cassandra.db.Keyspace.initCf(Keyspace.java:312)
        at org.apache.cassandra.db.Keyspace.<init>(Keyspace.java:269)
        at org.apache.cassandra.db.Keyspace.open(Keyspace.java:111)
        at org.apache.cassandra.db.Keyspace.open(Keyspace.java:89)
        at 
org.apache.cassandra.service.CassandraDaemon.setup(CassandraDaemon.java:364)
        at 
org.apache.cassandra.service.CassandraDaemon.activate(CassandraDaemon.java:567)
        at 
org.apache.cassandra.service.CassandraDaemon.main(CassandraDaemon.java:656)
DEBUG [main] 2015-07-22 15:05:19,002 AutoSavingCache.java (line 144) completed 
reading (21 ms; 0 keys) saved cache 
/home/cassandra/shared/saved_caches/urlapi_v2-DOMData-KeyCache-b.db
{noformat}

> key cache shrinks on restart
> ----------------------------
>
>                 Key: CASSANDRA-6574
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6574
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>         Environment: 1.2.12 + patches
>            Reporter: Chris Burroughs
>         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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