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From Michał Michalski (JIRA) <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-6768) Refresh permissions cache in ClientState periodically to avoid cache miss stampede effect
Date Tue, 25 Feb 2014 17:04:19 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-6768?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13911722#comment-13911722
] 

Michał Michalski commented on CASSANDRA-6768:
---------------------------------------------

Good point! So how about using them both (refresh and expire) to make it possible to set validityPeriod
>> refreshPeriod?
I don't have a strong opinion about the numbers, but let's say we could expire this cache
every 30 seconds and refresh every 3 seconds for example or something like this. 

> Refresh permissions cache in ClientState periodically to avoid cache miss stampede effect
> -----------------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-6768
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6768
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Michał Michalski
>            Assignee: Aleksey Yeschenko
>              Labels: authentication
>
> h3. Background
> We want to password-protect Cassandra by using the built-in PasswordAuthenticator and
PasswordAuthorizer. In general we are happy with this solution, but after reviewing the code
we're a bit afraid of default  permissionsCache behaviour in org.apache.cassandra.service.ClientState.
> h3. Problem
> From what I understand, at the moment cache expires every N seconds (2 by default) and
it gets repopulated when permissionsCache.get() is being  called. However, as we're talking
about at least a few hundreds requests to Cassandra per second, we're afraid of the "stampede"
effect once the cache expires and a number of queries will "trigger" its reload simultaneously
during the short period of time when it will be empty.
> h3. Proposed Solution
> Therefore, instead of the current solution, we'd prefer this cache to be reloaded "in
background" every N seconds, so it's only a single request every N seconds, rather than tens
(hundreds?) of them just after the cache expires during the period when it's empty.
> In other words, we're thinking about replacing this:
> {code}expireAfterWrite(validityPeriod, TimeUnit.MILLISECONDS){code}
> with:
> {code}refreshAfterWrite(refreshPeriod, TimeUnit.MILLISECONDS){code}
> Default refreshPeriod could be the same as the validityPeriod, for example.
> Are there any reasons that make this idea a bad one ("you misunderstood Guava's Cache"
counts too!)?
> [~iamaleksey], I've let myself to assign this issue directly to you, as you're the author
of current solution.



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