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https://issues.apache.org/jira/browse/HTTPCLIENT-1310?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13576476#comment-13576476
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Francois-Xavier Bonnet commented on HTTPCLIENT-1310:
----------------------------------------------------
To limit the number of requests sent to the remote server first note that there
is only one revalidation request per url or variant at the same time in the
queue.
In addition there are 2 settings you can play with:
# the max number of asynchronous workers
# the size of the revalidation queue
In most cases this limits will keep resource consumption acceptable.
I think you should be able to retrieve a stale cached document without
triggering a revalidation by adding in the request a directive Cache-Control:
max-stale= _delta-seconds_
> 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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