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From "Nikola Petrov (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HTTPCLIENT-1395) Call the storage implementation only once on a cache miss
Date Tue, 03 Sep 2013 13:21:55 GMT

     [ https://issues.apache.org/jira/browse/HTTPCLIENT-1395?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Nikola Petrov updated HTTPCLIENT-1395:
--------------------------------------

    Attachment: call-storage-implementation-once-trunk.patch
                call-storage-implementation-once-4.2-branch.patch

Hi, Oleg

Here are two patch files for 4.2 and for trunk. I exposed the methods in the HttpCache as
you suggested. Also I added a new CacheConfig variable in trunk to control if the client should
try to ignore the response if there is a newer in the cache as described here http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html#sec13.2.5
                
> Call the storage implementation only once on a cache miss
> ---------------------------------------------------------
>
>                 Key: HTTPCLIENT-1395
>                 URL: https://issues.apache.org/jira/browse/HTTPCLIENT-1395
>             Project: HttpComponents HttpClient
>          Issue Type: Improvement
>          Components: HttpCache
>    Affects Versions: 4.2.5
>            Reporter: Nikola Petrov
>            Priority: Minor
>             Fix For: 4.3.1
>
>         Attachments: call-storage-implementation-once-4.2-branch.patch, call-storage-implementation-once.patch,
call-storage-implementation-once-trunk.patch
>
>
> I am trying to use the httpclient-cache component with a Cassandra backend. Everything
seems good except that HttpCacheStorage#getEntry is getting called 3 times the first time
resulting in a performance bottleneck. There might be a way to handle this in the Storage
implementation by caching the recently queried values but I think that a better place is in
the CachingHttpClient class. The current code expects zero latency to the storage backend(the
current implementations are all memory based) but here is a patch that fixes the problem.
Some notes:
> * I am using the code from the 4.2.5 release(but can port the code to the current trunk)

> * test is provided in org.apache.http.impl.client.cache.TestCachingHttpClient
> * BasicHttpCache is patched to expose methods that check if the key is found or if a
proper variant is found - without this there is no way to say if there was a real cache miss
or the specific variant is missing
> * CachingHttpClient is checking if the current HttpCache implementation is BasicHttpCache
so it can use the new methods - I didn't want to change the interface because this will add
breaking changes to the API
> * This exposes the alreadyHaveNewerCacheEntry method so implementations can control if
the client should check for a more recent version in the cache

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