this post was submitted on 13 Jun 2023
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PHP
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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.