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From Alex Stewart <a...@foogod.com>
Subject Re: [PATCH] performance patch for mod_log_config
Date Mon, 10 Sep 2001 12:19:02 GMT
Brian Pane wrote:
> William A. Rowe, Jr. wrote:
> 
>> Is this the right place to be caching, or should this become a 
>> straightforward
>> optimization to apr's time.c functions?  I'd think the advantages are 
>> many for
>> keeping 15 current seconds in apr, and would pay off across the 
>> board.  Within
>> apr, we can always recalculate just the ms as well, for fun.
>>
> I think putting it in APR would work.  The one limitation I can think of
> is that adding the cache in apr_explode_localtime() itself wouldn't be a
> win because we'd have to add the overhead of a gettimeofday() call to
> check whether the supplied time was indeed current (and thus susceptible
> to caching).

I'm not that familiar with the usage patterns of this function in Apache 
et al, but it seems to me that a gettimeofday() call could be avoided 
reasonably well by simply tracking the previously-used time argument. 
If the current call is for a time which is later than the one of the 
last call (within a certain margin), cache it.  This should be just 
about as effective as checking gettimeofday() (possibly moreso, as it 
would also match anything within a reasonable proximity of the current 
time).  It might miss one or two if there are long periods without a 
call, but in that situation it's arguable that the speed of this 
function probably isn't the largest concern anyway.

Just a thought..

-alex


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