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From Jon Moore <j...@apache.org>
Subject Re: performance issue with CachingHttpClient
Date Wed, 04 Jul 2012 09:42:47 GMT
Hi Sam,

The client can't use the responseDate on the HttpCacheEntry because it
isn't the same thing as the value of the Date header from the server
response. The responseDate is the (local) time at which the response was
received. If you look at the RFC2616 specification for how to calculate the
age of an entry, it treats this value distinctly from the Date header value
on the response.

That said, there is probably some benefit to not parsing this over and over
again. Please open an Improvement ticket on the HttpClient JIRA so we can
track this:
https://issues.apache.org/jira/browse/HTTPCLIENT

And, as always, patches welcome. :)

Jon

On Tue, Jul 3, 2012 at 9:55 AM, Sam Perman <sam@permans.com> wrote:

> Hello
>
> 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
>
> thanks for any advice
> sam
>
> ps - 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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