Changing the architecture will likely get you the most bang but note
also that there are a few knobs that you can turn on the transient
object container UI that may limit the number of conflicts (in the
temp_folder/session_data_container):
- "Data object timeout value" -- the timeout value in minutes.. make
this higher.
- "Timeout resolution" -- the timeout resolution in seconds.. make
this higher.
You can also turn off "inband housekeeping" of session data by
calling the method "disableInbandHousekeeping" on a transient object
container. At that point, sessions will continue to work properly
but "old" session data won't be garbage collected and you will need
to do this every so often by calling the "housekeep" method on TOC.
See this written by dunny about conflicts and sessions (although this
was written before MVCC):
http://www.plope.com/Members/dunny/conflicts/view
HTH,
- C
On Nov 16, 2005, at 6:18 PM, Dennis Allison wrote:
Chris,
I am aware that using ZEO to back session database is likely to
increase
the opportunity for conflicts, but using a single session database
seems
to be reaquired if you want, as we do, to distribute out interactive
application acrosss a cluster of processors cleanly.
Under our current approach, we have multiple Zopes running on multiple
machines, all referencing a shared database of session variables.
This allows a HTTP request to be blindly distributed to any of the
machines. Given the conflict problems, we may need to rethink this
simplistic architecture.
On Tue, 15 Nov 2005, Chris McDonough wrote:
On Nov 15, 2005, at 5:54 PM, Dennis Allison wrote:
Has anyone prepared a set of best practice guidelines on the
techniques to
use to minimize conflicts?
It is becoming clear that we need to do to refactor some of our
code to
get us out of our current conflict pickle.
A quick google produced lots of commentary but nothing I could hand
to our
programmers as guidelines.
Nothing in general except the (probably too general) "attempt not to
allow one process/thread to write to the same object at the same time
as another process/thread".
One tip, since you've told us you use sessions heavily: using ZEO to
back your session database provides more opportunity for conflicts
than if you used a "normal" Zope storage. This is because:
- the opportunity for conflict naturally grows as transaction time
increases and using a ZEO storage rather than a local storage adds
latency to the total transaction time that would not otherwise exist.
- you have "n" processes attempting to write to essentially the same
objects at the same time when you use a shared ZEO sessioning
database. If these were instead local databases, each process would
only compete "with itself" (between all of its threads).
I tend to try to use local sessioning databases backed by tempstorage
plus a frontend load balancer that allows for cookie-based session
affinity (Pound).
- C
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