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From "Paul J. Reder" <rede...@remulak.net>
Subject Re: Speaking of pipes from cgis causing trouble...
Date Wed, 02 Oct 2002 02:35:07 GMT


William A. Rowe, Jr. wrote:

> At 03:27 PM 10/1/2002, Paul J. Reder wrote:
> 
> 
>>Ryan Bloom wrote:
>>
>>
>>>On Tue, 1 Oct 2002, Paul J. Reder wrote:
>>>
>>>
>>>>I've been working on the caching code and ran across a core dump...
>>>>
>>>>A particular file contains an SSI call to a cgi. The cgi causes a pipe
>>>>bucket to pass down the chain. cache_in_filter tries to save the bucket
>>>>away and core dumps.
>>>>
>>>>Since a pipe bucket can be of any length, and could take any amount of
>>>>time to complete, I would assume that the cache code should decide not
>>>>to cache any response with a pipe bucket, correct?
>>>>
>>>Not necessarily.  The cache code should stream the data to the cache, and
>>>allow the data to also stream to the core_output_filter.
>>>
>>Until it reaches the specified max cache size?
>>
>>So instead of trying to just copy and insert the pipe bucket, it should read
>>
>>from the pipe and add buckets to the cache (and forward copies on)? Seems
> 
>>like it would defeat some of the sendfile optimizations and such... Is it worth
>>the code and lost optimizations to read/store/pass the piped data?
>>
> 
> Not if you read off the headers, determine cacheability, and then send the
> remaining pipe bucket down and ignore it when we can't cache the result
> anyways.  If the resource can be cached, the penalty for reading and then
> storing + sending is nothing when you weigh serving out of the cache,
> next time around.


Well, considering that we wouldn't even be in the core dumping code if it hadn't

passed the cacheability checks, I think *this* part is safe. My concern was more

along the lines of, how much are we worried that reading and storing pipe buckets

will result in wasted cycles when the cache entry has to be tossed after exceeding

the specified maximum size. Is the potential cache gain worth the price of reading,
storing, and passing the pipe contents given the potential for having to toss it
for growing too big?

If the probability of tossing is low, or largely under user configuration control,

then I'll adjust the cache code to be able to read and store pipe and socket bucket
contents. Are there any other bucket types to worry about (i.e. that can't just be
copied)?

-- 
Paul J. Reder
-----------------------------------------------------------
"The strength of the Constitution lies entirely in the determination of each
citizen to defend it.  Only if every single citizen feels duty bound to do
his share in this defense are the constitutional rights secure."
-- Albert Einstein



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