> 2. The RowDescription ('T') message is extended by adding a new value
> for each field. Just after the type-size value, there will now be
> an int16 "atttypmod" value. (Would someone provide text specifying
> exactly what this value means?) libpq will store this value in
> a new "adtmod" field of PGresAttDesc structs.
From src/include/catalog/pg_attribute.h:
/*
* atttypmod records type-specific modifications supplied at table
* creation time, and passes it to input and output functions as the
* third argument.
*/
Currently only used for char() and varchar(), and includes a 4-byte
header.
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