Martin Meinhold created HTTPCLIENT-1310:
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Summary: 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
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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