[mod_python] Reloading PSP sometimes shows old pages

2009/3/30 Mike Mueller <mike at subfocal.net>:
> On Mon, Mar 30, 2009 at 05:09:08PM +1100, Graham Dumpleton wrote:
>> 2009/3/30 Mike Mueller <mike at subfocal.net>:
>> > The URL has no query string, it's just http://host:81/~mike/test/page.psp.
>> > No POST parameters or anything, a very simple page.
>> >
>> > No proxy.  Browser is on the same host as Apache.  As I said in the
>> > first email, no caching in Apache, as far as I can tell.  (I grepped
>> > around the config files looking for any caching that might've been
>> > enabled by default, and came up empty.)
>> >
>> > The more I play with it, the more I think it may just be Firefox that
>> > sucks.  The bouncing-between-versions only happens in it.  I thought
>> > Opera had it because the first time I loaded my page in Opera, I got an
>> > old version (several versions prior) of the page.  That was before
>> > changing MaxRequestsPerChild.  But I haven't seen that in Opera since.
>> >
>> > Opera's only problem is that reload doesn't always update to latest...
>> > sometimes I have to navigate away and come back, or it'll keep showing
>> > me the version it has loaded.  (I've tried various combos of shift,
>> > ctrl+shift, etc. while clicking reload).
>> >
>> > Also, after a certain length of time (a minute or two?), both browsers
>> > simply load the latest version, with no weird old versions appearing.
>> >
>> > This is frustrating.
>>
>> All I can suggest is that log using req.log_error() from the PSP page
>> and include in the response of the page, both the date/time and the
>> process ID.
>>
>> Logging will help to verify if page actually being processed. It being
>> in the page should make it easier to verify that data is actually
>> changing or not. If that part of data changes but remainder of page
>> doesn't then would have to be a caching issue with mod_python and
>> MaxRequestsPerChild isn't working.
>>
>> See if that shows any pattern. Logically every request should have a
>> different date/time and pid if MaxRequestsPerChild is set to 1.
>>
>> Graham
>
> Thanks for all the help.  I'm still confused. :)
>
> I printed the request time, the mtime, and the PID on every page.  The
> result looks like this:
>
> Request time: Mon Mar 30 00:00:00 2009
> Modify time:  Wed Dec 31 00:00:00 1969
> PID:          6379
>
> That's req.request_time and req.mtime passed through datetime's ctime()
> function.  (i.e. datetime.date.fromtimestamp(req.mtime).ctime()). I'm
> not sure if it indicates a problem, or if the request object simply
> doesn't bother filling in the times correctly.

There isn't such a thing as req.request_time.

The req.mtime value will not be anything meaningful for PSP stuff
under mod_python.

Use time.asctime().

> For example, the PSP documentation says:
>> When a file is used as the source, the code object resulting from the
>> specified file is stored in a memory cache keyed on file name and file
>> modification time. The cache is global to the Python interpreter.
>> Therefore, unless the file modification time changes, the file is
>> parsed and resulting code is compiled only once per interpreter.
>
> Is it possible that this incorrect mtime is affecting PSP's internal
> page caching algorithm?

No, doesn't look at it. It does it own call of os.path.getmtime().

> By the way, the resulting behavior after this change is:
> F5 F5 F5 -> keeps showing the same PID.  Hit F5 thirty times and the PID
> jumps up a couple times, 6379, 6388, 6401, and then stays at 6401 for a
> while.  If I go 'touch' the common.psp source file, it doesn't seem to
> cause Firefox or Opera to see a new page.  They keep seeing the old one
> for some arbitrary period of time.

But did you add logging for Apache error log to see if each page hit
actually resulted in mod_python even handling the request. At the same
time, look at Apache access log to see if any request registered
there.

Graham