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https://issues.apache.org/jira/browse/HTTPCLIENT-1310?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13583135#comment-13583135
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Francois-Xavier Bonnet commented on HTTPCLIENT-1310:
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Jon,
The code quality is good and the patch includes good unit tests, but before I
commit anything I would like to have your opinion on some points:
* this new feature introduces a failure cache (the default implementation is
based on a ConcurrentMap). Is it consistent to have separate caches for http
responses and for failures? Wouldn't it be better to store failure information
in the existing cache with http responses?
* in the patched version, the backoff strategy is implemented by a class
SchedulingStrategy class that can be used only when doing asynchronous
revalidation. For me it would make sense to be able to apply this backoff
strategy also when doing synchronous revalidation
* if the goal is to avoid sending requests again and again when the backend
server is down, don't you think it would be more efficient to stop all requests
to this host? It would look like what Apache connectors do when a worker is
considered in error state. Then this would be a feature for HttpClient project
that could be used even without cache.
Your opinion?
> Allow background validation to optionally back off after a number of failed
> requests
> ------------------------------------------------------------------------------------
>
> Key: HTTPCLIENT-1310
> URL: https://issues.apache.org/jira/browse/HTTPCLIENT-1310
> Project: HttpComponents HttpClient
> Issue Type: Improvement
> Components: Cache
> Reporter: Martin Meinhold
> Attachments:
> 0001-HTTPCLIENT-1310-Allow-clients-to-change-the-used-sch.patch
>
>
> We are successfully using the background validation to asynchronously update
> cache entries while returning a stale document (stale-while-revalidate cache
> control header). Also in case an error has happened, the stale document is
> used (stale-if-error cache control header). Works perfectly. Guys - great
> work you made this happen.
> Now the tricky part: as soon there is an issue like e.g. the remote server is
> down, the stale-if-error header prevent the cache from being updated (which
> of course is the intention of that header). But this also means, that code
> using the HttpClient has no way to discover that there was an issue. So every
> following request will get that stale document but also trigger a background
> revalidation.
> As an improvement it should be possible that the background validation backs
> off after a certain amount of failed requests. This should be optional and
> not the default.
> I want to contribute some code we already have working on a 4.2 branch. The
> central idea is to vary the scheduling strategy the AsynchronousValidation
> uses to estimate _when_ the background validation of a certain request should
> happen. Of course, the default would be immediately.
> In fact this would move code currently submitting tasks to the executor from
> the AsynchronousValidation into a separate class. Thus the
> AsynchronousValidation would become kind of a director role by simply
> enqueuing next requests and keeping track which of them failed and which were
> successful. A strategy could - based on the failure count - execute them
> immediately or later. Again, to clarify: the default behaviour would be to
> execute every incoming background validation request immediately regardless
> of the error count.
> What do you think?
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