When connecting to a PostgreSQL Version 8 database, pq connection fails with:

[reporting]: 2013/12/05 14:47:59 driver: bad connection

Diagnosis:

In PostgreSQL 8.1 the maximum value for extra_float_digits is 2. In PostgreSQL 9 the maximum was increased to 3. From the PostgreSQL Release Notes:

Allow server parameter extra_float_digits to be increased to 3 (Tom Lane)

The previous maximum extra_float_digits setting was 2. There are cases where 3 digits are needed to dump and restore float4 values exactly. pg_dump will now use the setting of 3 when dumping from a server that allows it.