[jira] [Assigned] (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:all-tabpanel ]

Michał Michalski reassigned CASSANDRA-6768:
-------------------------------------------

    Assignee: Michał Michalski  (was: Aleksey Yeschenko)

> 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: Michał Michalski
>              Labels: authentication
>
> h2. 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.
> h2. 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.
> h2. Proposed Solutions
> 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 two solutions (updated after comments from [~jjordan] and [~iamaleksey]):
> h3. Make the ClientState's permissionsCache configurable. 
> Let's define additional configurable variable called refreshPeriod and make it 0 by default (0 means no refresh - nothing changes in current code). If it's > 0, add the refreshAfterWrite to the existing code.
> This way we keep the defaults "safe", but add possibility to "tune" the cache when someone needs it. Any cons?
> h3. Make Authorizer responsible for its own cache
> As I said, I believe that Authorizer should be responsible for defining its cache, so I'd prefer to add a getPermissionsCache method to IAuthorizer and get rid of the cache creating code in ClientState. Of course it's a bigger change, it breaks the existing interface, but from my point of view it's the better choice. 
> Of course there's no problem to combine these two options and make the per-Authorizer cache configurable.



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