No explicit USE database statement

[TheLevti]

No need to explicitly send a USE database statement. The database is already selected via the DSN string.

Multiple reasons for this:

• One less round trip per connection
• No connection pinning when used with a proxy (e.g. RDS Proxy).
• No other drivers are doing that (again, database is already selected via the DSN string).

[GrahamCampbell]

This cannot be removed. It's necessary when persistent connections are enabled. It's also necessary for other MySQL compatible databases.

[TheLevti]

This cannot be removed. It's necessary when persistent connections are enabled. It's also necessary for other MySQL compatible databases.

Can you elaborate why this is needed for persistent connections? Also, which other mysql databases? If they are mysql compatible, then I would assume they also allow the database to be specified in the DSN.

We currently have the problem that we first of all need to get rid of any unnecessary round trip to the DB and also avoid connection pinning via RDS proxy. This non configurable behaviour forces us to overwrite this class or use a custom driver in all services. It would be nice if this can be solved directly on the framework. Same as all the other optional SET operations (timezone, mode, charset etc.)

Based on docs I have found, if the database is specified in the DSN, PDO takes care of ensuring that the right DB is selected (even for persistent connection). So it is not necessary to send out another USE statement on application level.

We have been using persistent connections for quite some time (with cakephp, there no explicit USE call is done), and we never had to send an explicit USE statement. (We use AWS Aurora MySQL + MySQL locally).

Proposal:

To be 100% backwards compatible just in case (if you don't trust it to be like I described), allow setting a new config value to skip setting the database explicitly.

Edit:
Even chatgpt o1 mentions this:

Short Answer: If you include the database name in your DSN (for example, mysql:host=localhost;dbname=your_database), PDO will internally issue a USE your_database statement whenever it (re)establishes a persistent connection, so you generally do not need to issue USE $database yourself. However, if you do not specify dbname=... in your DSN, then you should issue USE $database after you connect in order to guarantee you are using the correct default schema—persistent connections can be re-used in unpredictable states.

[GrahamCampbell]

I'd rather see this in 12.x as a breaking change.

[GrahamCampbell]

In my experience, this is pretty unreliable, and this may cause subtle bugs for people.

[GrahamCampbell]

oh, nvm. i see config got added, and it defaults to the same behiavour. :P

[TheLevti]

Thanks guys! This saves us some work.

[it-can]

@TheLevti maybe add a config option to the docs/config files describing this option?

[TheLevti]

@TheLevti maybe add a config option to the docs/config files describing this option?

Will do that.