Description
bool 
pg_trace ( string pathname [, string mode [, resource connection]] )
   pg_trace() enables tracing of the PostgreSQL
   frontend/backend communication to a file. To fully understand the results,
   one needs to be familiar with the internals of PostgreSQL
   communication protocol.
  
For those who are not, it can still be
   useful for tracing errors in queries sent to the server, you
   could do for example grep '^To backend'
   trace.log and see what queries actually were sent to the
   PostgreSQL server. For more information, refer to the
   PostgreSQL Documentation.