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I haven’t used persistent connections although I have been tempted in the past. I believe, if you haven’t used it before, it might come with more trouble than it solves.
As an alternative I could propose using amphp (or maybe react PHP) which will let you handle a pool of connections in a single long running process. But it’s a bigger change really, the more I think of it.
Yeah, but any ‘single server’ PHP defeats the purpose of PHP, so I’m not a huge fan.
I’ve used them in the past, and they work great, until you have to switchover to another node.
Fair point.
However why do you need persistent connections ? I am thinking that the growing rate of the connections should be very low as the instances increase, given that the queries are quick.
You lose about 5-6ms just connecting to the database. Keeping them open helps a lot.
My goal is to write as simple code as possible, and everything else is super quick, just the connections aren’t handled well in PHP. Which is a shame.
It’s not that there isn’t the option, it’s just that I don’t know how to help you. MySQL has an option to reconnect, I suppose might be the same for postgres?
The single running process that was so easily dismissed, could save tons of queries, for example! Sorry I keep thinking about that direction
Single process doesn’t save any queries, no idea what you mean.
Persistent connections persist between requests just like in a single process. It’s just that pool handling is hidden in PDO.
Also how’s the setup? You setup for example 5 max children in fpm and 5 persistent connections? Per server? So your overall connections to the db server will be 5x your server instances?
If you setup 5 fpm children and less connections, one child will eventually reuse from another, but only when the connection is free (does not do a query for another process or pdo does not consume a resultset). If it tries to do a query at that time it will have to wait and it will block. This is my understanding. Also how you do transactions with persistent connections?
This has evolved into such an interesting conversation.
From my current understanding, there is no pool, just one process keeps and reuses one database handle over and over again.
And it’s not PDO, but the driver, which handles that.
Transactions are handled within try/finally blocks. You can reset the DB connection, but it’s not free in terms of time. You get more performance making sure code doesn’t leak open transactions.