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From "Sam Perman (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HTTPCLIENT-1213) performance issue with CachingHttpClient
Date Thu, 05 Jul 2012 13:07:35 GMT

     [ https://issues.apache.org/jira/browse/HTTPCLIENT-1213?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Sam Perman updated HTTPCLIENT-1213:
-----------------------------------

    Attachment: httpclient-1213.patch

Here is a proposed fix for this issue. It will parse the Date header with the HttpCacheEntry
is created rather than each time it is accessed.
                
> performance issue with CachingHttpClient
> ----------------------------------------
>
>                 Key: HTTPCLIENT-1213
>                 URL: https://issues.apache.org/jira/browse/HTTPCLIENT-1213
>             Project: HttpComponents HttpClient
>          Issue Type: Improvement
>          Components: Cache
>    Affects Versions: 4.2 Final
>            Reporter: Sam Perman
>             Fix For: 4.3 Final
>
>         Attachments: httpclient-1213.patch
>
>
> We're using the CachingHttpClient and are seeing a spike in CPU usage when it is enabled.
We've profiled our application and see that most of the time is being spent parsing dates.
Specifically, it is trying to get the age of a cache entry on a cache hit by parsing the "Date"
header on the HttpCacheEntry.  I had a couple questions:
> 1) Why can't this use the responseDate value that lives on HttpCacheEntry? (This would
avoid the overhead of parsing)
> 2) If it needs to parse, is it possible to remember the result on the HttpCacheEntry
so it doesn't need to be parsed every time?
> We are using version 4.2
> Here is the full backtrace we are seeing:
> org.apache.http.impl.cookie.DateUtils.parseDate(String)
>   org.apache.http.impl.client.cache.CacheValidityPolicy.getDateValue(HttpCacheEntry)
>     org.apache.http.impl.client.cache.CacheValidityPolicy.getApparentAgeSecs(HttpCacheEntry)
>       org.apache.http.impl.client.cache.CacheValidityPolicy.getCorrectedReceivedAgeSecs(HttpCacheEntry)
>         org.apache.http.impl.client.cache.CacheValidityPolicy.getCorrectedInitialAgeSecs(HttpCacheEntry)
>           org.apache.http.impl.client.cache.CacheValidityPolicy.getCurrentAgeSecs(HttpCacheEntry,
Date)
> There are a couple callers to "getCorrectedAgeSecs":
> CacheValidityPolicy.isResponseFresh(HttpCacheEntry, Date)
>   CachedResponseSuitabilityChecker.isFreshEnough(HttpCacheEntry, HttpRequest, Date)
>     CachedResponseSuitabilityChecker.canCachedResponseBeUsed(HttpHost, HttpRequest, HttpCacheEntry,
Date)
>       CachingHttpClient.handleCacheHit(HttpHost, HttpRequest, HttpContext, HttpCacheEntry)
> CachedHttpResponseGenerator.generateResponse(HttpCacheEntry)
>   CachingHttpClient.generateCachedResponse(HttpRequest, HttpContext, HttpCacheEntry,
Date)
>     CachingHttpClient.handleCacheHit(HttpHost, HttpRequest, HttpContext, HttpCacheEntry)
> Looking at the code, it looks like this section from CachingHttpClient.handleCacheHit
will result in parsing the date twice (apologies if I'm misreading this)
> if (suitabilityChecker.canCachedResponseBeUsed(target, request, entry, now)) {
>     return generateCachedResponse(request, context, entry, now);
> }
> Both the call to "canCachedResponseBeUsed" and the call to "generatedCachedResponse"
will ultimately call "getCurrentAgeSecs" and parse the Date header.

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