Am 15.01.2012 13:22, schrieb Peter Otten:
Heiko Wundram wrote:
I agree completely with that (I hit the corresponding problem with suds
while transitioning from 32-bit Python to 64-bit Python, where hashes
aren't stable either), but as stated in my mail: that wasn't the
original question. ;-)
I'm curious: did you actually get false cache hits or just slower responses?
It broke the application using suds, not due to false cache hits, but
due to not getting a cache hit anymore at all.
Long story: to interpret WSDL-files, suds has to get all related DTDs
for the WSDL file, and Microsoft (as I wrote I was querying Exchange Web
Services) insists on using http://www.w3.org/2001/xml.dtd for the XML
spec path. This path is sometimes functional as a GET URL, but mostly
not (due to overload of the W3-servers), so basically I worked around
the problem by creating an appropriate cache entry with the appropriate
name based on hash() using a local copy of xml.dtd I had around. This
took place on a development machine (32-bit), and when migrating the
application to a production machine (64-bit), the cache file wasn't used
anymore (due to the hash not being stable).
It's not that this came as a surprise (I quickly knew the "workaround"
by simply rehashing on the target machine and moving the cache file
appropriately), and I already said that this is mostly just a plain bad
design decision on the part of the suds developers, but it's one of
those cases where a non-stable hash() can break applications, and except
if you know the internal workings of suds, this will seriously bite the
developer.
I don't know the prevalence of suds, but I guess there's more people
than me using it to query SOAP-services - all of those will be affected
if the hash() output is changed. Additionally, if hash() isn't stable
between runs (the randomized hash() solution which is preferred, and
would also be my preference), suds caching becomes completely useless.
And for the results, see above.
--
--- Heiko.
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