[jira] [Comment Edited] (CASSANDRA-6768) Refresh permissions cache in ClientState periodically to avoid cache miss stampede effect

["Michał Michalski (JIRA)" <ji...@apache.org>]

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

Michał Michalski edited comment on CASSANDRA-6768 at 2/25/14 5:04 PM:
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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 on 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. So no matter how ofter we update, old entries will eventually expire, if I understand the Guava docs correctly.


was (Author: michalm):
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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