Re: Dealing with lost database connections

You can use the same basic approach, in various ways.  If you use a
connection pool, override the onHandOut() method and use a custom pool
(also look at the default implementation).  Every time you the pool
issues a connection it will perform a test, if you want it to.  That
may be more testing than you feel like doing.  (Er, I haven't tested
the pools much; I think there are a couple of tests in the suite, but
I haven't banged on them heavily.)  Or, you can, at any time you wish,
test the connection as follows:

   if not mySelectTest(db.conn):
	del db.conn
   # proceed

DBIBase.conn is a property.  The connection it returns is stored in
thread local storage; if you delete it, the connection is closed and
the next time you access it, a new connection will be created for you.
(And of course, a new connection will be created if you access it in a
different thread -- don't try to bring a transaction across threads,
it won't work!)  

In a web application, for instance, you might want to perform such a
test at most once per request; it may not be once per transaction. 

I hope that helps!

js
   

On Fri, Jul 22, 2005 at 01:10:29AM +0100, Hamish Lawson wrote:
> It is common to cut down on the cost of opening a database connection
> for each request by opening the connection once and reusing it for
> subsequent requests (assuming the application is being handled by some
> long-running process). However if the database goes temporarily
> offline (say for backing up) then the connection may become
> invalidated. Before using PyDO I dealt with this by wrapping the
> connection in a class that detects such invalidation and creates a new
> connection as necessary. How is this situation dealt with when using
> PyDO? Given that PyDO creates its own connections, it doesn't seem as
> if I can use my previous approach.
> 
> 
> Hamish Lawson
> 
> 
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-- 
Jacob Smullyan

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