Re: This connection has been closed

On 06/12/11 15:55, Samuel Gendler wrote:
>
> If you're using a 3rd party connection pool, I don't believe there is
> a contract that they will necessarily validate that a connection is
> still open before returning it. Most pools can be configured to issue
> a 'select 1' type of query on a periodic basis to keep connections
> from timing out, or just to validate that a connection is still alive
> before returning it from the pool.
>

Relying on that alone is madness, because there's an inevitable gap
between the `SELECT 1;' succeeding and the connection being passed to
the app, and that's time the connection can become invalid during. It's
a race, bascially. Because that race can't be eliminated the app still
has to be coded to be fault-tolerant and cope with failed transactions.

Validating connections is still useful if your app's idea of
fault-tolerance is telling the user "something broke, please try again".
You want to minimise how often that happens, so you try to make sure
your pool notices a database restart promptly and flushes its connections.

If your app has better fault tolerance than that, where it remembers
what it tried to do and does it again if a transaction fails the first
time, then there may be no point validating connections at all.

--
Craig Ringer