Excessive number of queries for metadata by PDO

[repli2dev]

Version: 2.4.6

When analysing queries from the DB side (PostgreSQL) we have discovered that the PDO is making a excessive number of queries for pgclass and pgtype... We investigated that these queries origin from PDO extension itself (hence not visible in any query monitoring done on PHP runtime) and are caused by nette/database from Helpers::detectTypes() where PDO::getColumnMeta() is called.

The excessiveness is that we have around 500 queries on page and this generates around 1500 additional queries (depends on number of columns and custom types), which are quite fast, but still takes around 5% of whole request.

Could the method detectTypes() be efficient? Maybe caching? (However that may not be a good idea as schema can change during execution.)

[dg]

Are these queries similar?

[repli2dev]

@dg yes, only OID changes and in high numbers they are event duplicate... See pgsql_stmt_get_column_meta in https://www.askapache.com/pub/php/ext/pdo_pgsql/pgsql_statement.c

[repli2dev]

This solves our issue only partially (for the exact duplicate queries) thanks for that! ... Though I am not able to came up with any better solution as the the queries with different param values cannot be cached... The same for different queries referencing same table columns (i.e. both referencing foo.my_column) due to the fact that DBAL doesn't really know they are the same columns and asks for 0..n column`s metadata.

So this is probably all what can be done if the library doesn't want to obtain all this metadata bypassing the PDO (and with using caching)... which is probably overkill and will probably not gain anything speaking of performance.