Under mod_perl, our programs use persistent database connections - so once established, a connection will generally stay connected. Each time a GMail request starts, it gets one of the pre-established database connections, and when it's done it releases it back so that one of the next GMail requests can reuse the connection. This effectively eliminates the database connection overhead and results in a fairly decent optimization. A new connection will be created only if no connections are available when the connection needs to be established.

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Jason Rhinelander
Gossamer Threads
jason@gossamer-threads.com