Re: PyDO2: How to handle DB restart?

On Sat, Jun 24, 2006 at 02:34:31PM +0200, Faber wrote:
> Hello,
> 
> I'm using PyDO2 with PostgreSQL in a web application, hosted by a thirdy 
> party provider, using a connection pool:
> 
> db_pool = ConnectionPool(
> 	max_poolsize=10,
> 	keep_poolsize=0,
> 	delay=0.2,
> 	retries=10
> )
> 
> Sometimes the hosting restarts the PostgreSQL server, and I get this 
> exception in my Python code (even *after* the server has been restarted):
> 
> "ProgrammingError: terminating connection due to administrator command
> server closed the connection unexpectedly
>         This probably means the server terminated abnormally
>         before or while processing the request."
> 
> How could I avoid this exception?

Hi Faber --

I believe you want to subclass ConnectionPool and override onHandOut()
to perform an additional test on the connection, such as performing a
fast test query (a la "SELECT 1").  If onHandOut() returns False
you'll get a new connection.

Or, if the overhead of these tests is disagreeable (one test per
commit), you might be able to stick a hook in your web framework to
test one connection at request cleanup and reinitialize the pool if it
has gone sour.  However, if you tend not to use many transactions
per request it is probably OK.

Cheers,

js


> 
> Thank you
> 
> -- 
> Faber
> http://faberbox.com/
> http://smarking.com/
> 
> We live in a society exquisitely dependent on science and technology,
> in which hardly anyone knows anything about science and technology. -- Carl 
> Sagan
> 
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Jacob Smullyan

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