[jira] Resolved: (CASSANDRA-1966) Option to control how many items are read on cache load

["Jonathan Ellis (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CASSANDRA-1966?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Jonathan Ellis resolved CASSANDRA-1966.
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    Resolution: Won't Fix

I don't think this is going to have a good cost:benefit ratio.  If you want to get down to a 5 minute startup, for example, you'd be able to load under 10% of your cache which is basically useless.

I'm not sure it's possible to get good speed on the row cache loading.  Maybe if you did a sequential scan over all the sstables at once looking for rows matching the saved keys...  But even sequential i/o can be painful if you have enough data.

The reason you can't just save the entire row cache, by the way, is that if you save the cache hourly but updates come in between saves, if you just load the cache on startup then you have no way of knowing how stale it is... without rebuilding the cache.

> Option to control how many items are read on cache load
> -------------------------------------------------------
>
>                 Key: CASSANDRA-1966
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-1966
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Chris Burroughs
>
> CASSANDRA-1417 added an option to save the key and/or row cache keys which is cool.  However, for a row large cache it can take a long time to read all of the rows.  For example I have a 400,000 item row cache, and loading that on restart takes a little under an hour.
> In addition to configuring the size of the row cache, and how often it should be saved to disk, I propose an option to control how many items are loaded on startup (or alternately only saving n items out of the full row cache to begin with).

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