Ah, I see. I guess one option would be to offer as a service to
maintain the data on a MySQL database on your own server, but you may
not wish to get into such a long-term relationship. I have often
thought about the balance between offering product and offering a
service, and it's not obvious to me which might be better in general
-- only in particular.
George
On Jul 21, 2009, at 1:50 PM, Phil Davis wrote:
George C Brackett wrote:
Is the purpose of the online stack just to hold the value of the
custom property? If so, why not use a database such as MySQL or
PostgreSQL? These are carefully engineered to prevent collisions by
multiple users.
George
You're absolutely right, George - MySQL etc offer superior data
management capabilities. But often the introduction of a conventional
DBMS brings with it the need for more technical support. Most small
businesses (at least the ones this product serves) don't have a tech
support person on the payroll and want to keep it that way. By using
this simple dumb-data-on-server / smart-app-on-every-client approach,
even the owner of the company can usually restore the server data if
something goes wrong! Imagine that. ;-)
Phil
On Jul 20, 2009, at 7:59 PM, Phil Davis wrote:
I'm looking for the best way to detect data corruption ASAP after it
happens in a custom property of a stack. The stack resides on a file
server and is read & written by many clients. File locking during
reads and writes is already in place and seems to be doing its job,
but occasionally we still have data corruption that creeps in.
Specifically, I want to make a way for the "Client B" app to know
that the value it gets from the "uData" custom property of stack
"myStack" is exactly what the "Client A" app put there a moment
before.
Here's how I see this working:
* Client A
o (stack is in memory, file is locked on server)
o sets the uData of stack "myStack" to new value
o puts md5digest of updated uData into "dataDigest" file on
server
o saves "myStack" stack
o deletes stack from memory
o unlocks file on server
* Client B (a moment later)
o locks "myStack" file on server
o puts "dataDigest" file from server into tOldDigest
o goes to stack "myStack"
o puts md5digest of uData custom prop into tNewDigest
o if tNewDigest = tOldDigest, all is well; otherwise
corruption exists
Does anyone see a problem with this approach? Is there a better way
to accomplish the goal? If each client could check the data after
its own write without having to read the stack into memory again to
do so, that would be great - I just didn't see a way for that to
happen.
Thanks everyone -
--
Phil Davis
PDS Labs
Professional Software Development
http://pdslabs.net
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