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From <...@covalent.net>
Subject Re: file/mmap buckets, subrequests, pools, 2.0.18
Date Fri, 01 Jun 2001 20:49:14 GMT
On Fri, 1 Jun 2001, Greg Stein wrote:

> On Fri, Jun 01, 2001 at 11:00:08AM -0700, rbb@covalent.net wrote:
> >...
> > This is realitively simple.  A while ago, I changed the default handler to
> > use the connection pool to fix this problem.  A couple of months ago, Dean
> > pointed out that this was a major resource leak.  After 2.0.16, somebody
> > (Roy?) pointed out that this was a pretty big problem when serving a lot
> > of very large files on the same connection.
> >
> > The solution was a simple loop at the end of the core_output_filter that
> > reads in the data from the file to memory.  This is okay to do, because we
> > are garuanteed to have less than 9k of data.  It sounds like the problem
> > is that we don't read in the data if we have an MMAP, or we may not be
> > getting into the loop on sub-requests.
>
> What about the idea to have setaside() take a pool parameter? The bucket
> should ensure that its contents live at least as long as the pool.
>
> For an MMAP bucket, if the given pool is the same or a subpool of the mmap's
> pool, then nothing needs to happen. If the pool is a parent of the mmap's
> pool, then the bucket needs to read its contents into a new POOL bucket
> attached to the passed-in pool.
>
> Other buckets operate similarly. This would ensure that we can safely set
> aside any type of bucket, for any particular lifetime (whether that is for a
> connection or a request or whatever).

Yes, that would work as well.  I am beginning to think that this is
overkill for our use cases, and it wouldn't really solve this problem,
since the sub_request_output_filter still wouldn't be calling setaside.
Also, when a regular filter calls setaside, which pool does it use?  I
would guess c->pool, but that could get confusing.

My only other concern is actually walking all the way back up to ensure
that the current pool is a decsendant of the pool passed to setaside.
Those tests should be quick, but we will be calling setaside a lot through
the course of some requests.  I am positive that we only want to do this
"copy anything under 9k to non-volatile location" in two places, whereas
setaside is potentially called from every filter.  If the setaside
function is ever called incorrectly, we will end up doing the copies far
more often than we need/want to.

Those are just my concerns though, not a reason not to do the work.  I
just figure that by getting this stuff out in the open early, we can avoid
some annoying head-aches.

Ryan

_______________________________________________________________________________
Ryan Bloom                        	rbb@apache.org
406 29th St.
San Francisco, CA 94131
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