[racket] db connection-pool tip

From: Neil Van Dyke (neil at neilvandyke.org)
Date: Wed Aug 22 13:15:38 EDT 2012

Ryan Culpepper wrote at 08/22/2012 12:12 PM:
> Your initial experience sounds like a bug, though; it sounds like the 
> connection didn't know it had been disconnected. What was the 
> underlying kind of connection?


Regarding "connected?"...  My d'oh moment was when I saw that the 
PostgreSQL log had messages, "EDT LOG:  unexpected EOF on client 
connection", appearing temporally at the end of the first use of the 
connection, approximately at the time that the connection was reclaimed 
by the pool.  (The first DB connection was for the lifetime of a 
short-lived thread, and the pool-of-pools created the "connection-pool" 
on-demand within that same short-lived thread.)  I then figured that the 
"connected?" procedure was reporting some state that was stored on the 
Racket side of the connection, which was still true -- although the 
answer was known to be false by the PostgreSQL server and perhaps by a 
lower networking layer on the Racket side.  If that's the case for 
"connected?" behavior, I suppose there might be a place for keeping that 
(which has good performance) and also adding a procedure with the 
different behavior of more expensive "really-connected?" and perhaps 

Server was PostgreSQL 8.4, talking over non-SSL'd TCP.

Thanks for looking at this.

Neil V.

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