Since ages, we transfer data between different DBS (Informix, Sybase, Oracle, and now PostgreSQL) with our own written tool, based on Perl::DBI which produces a CSV like export in a common way, i.e. an export of Oracle can be loaded into Sybase and vice versa. Export and Import is done row by row, for some tables millions of rows.
We produced a special version of the tool to export the rows into a format which understands the PostgreSQL's COPY command and got to know that the import into PostgreSQL of the same data with COPY is 50 times faster than with Perl::DBI, 2.5 minutes ./. 140 minutes for around 6 million rows into an empty table without indexes.
How can COPY do this so fast?
Probably there are more reasons
1. probably DBI implementation is not too effective (for Postgres), maybe because COPY is not fault tolerant
2. postgres has not implicit plan cache, so every INSERT planned again and again
3. COPY bypass planner and executor and it has very effective network communication
4. with COPY you have a sure so autocommit is disabled.
