no need for new test that covers this new exception throw ?

You're right, will update PR with test

This cannot be merged becausegetColumnMeta doesn't work with all drivers. Also this slows down every session with an additional query. And the additional query even selects every row and thus blocks every session inside the transaction.

If strict SQL mode is not enabled and you assign a value to a BLOB or TEXT column that exceeds the column's maximum length, the value is truncated to fit and a warning is generated. For truncation of nonspace characters, you can cause an error to occur (rather than a warning) and suppress insertion of the value by using strict SQL mode.

https://dev.mysql.com/doc/refman/5.0/en/blob.html

So for mysql enabling strict sql mode should be sufficient.
Also 64kbyte session storage is possible with BLOB.@gonzalovilaseca what is the use-case to store more data in the session?

@Tobion We store session in a Mysql in memory table therefore we cannot use blob or text, in our scenario the column can't be bigger than 21.000 chars.
Anyway we'll find a workaround for that, I don't see any neat solution for this in the PDO handler class.

So do you usevarbinary for the data column? It would give you 65,535 bytes, which is shared among all columns. Why only 21.000 bytes in your case?

@Tobion We are using varchar. Don't know exactly why, but it doesn't allow a value greater than 21k. Anyway we can solve the issue by writing fewer data to session, but the background problem still remains, allthough it seems that nobody has had it before. Should we just close thir PR?

Closed in favor ofsymfony/symfony-docs#5269 as the only thing we can do is documentation