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https://issues.apache.org/jira/browse/CASSANDRA-6768?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13913153#comment-13913153
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Michał Michalski commented on CASSANDRA-6768:
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I've updated the issue description.
I understand that I can just implement my own Authorizer and solve the problem
there, but - still - I think that current implementation (permissionsCache in
ClientState and the lack of cache configuration options in general) has some
space for improvements, so before I start to fiddle on my own, I'd like to tell
you what bugs me and how it could be improved ;-)
> 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
>
> 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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