This postgresql plugin provides metrics for your postgres database. It currently works with postgres versions 8.1+. It uses data from the built in pg_stat_database and pg_stat_bgwriter views. The metrics recorded depend on your version of postgres. See table:
pg version 9.2+ 9.1 8.3-9.0 8.1-8.2 7.4-8.0(unsupported)
--- --- --- ------- ------- -------
datid x x x x
datname x x x x
numbackends x x x x x
xact_commit x x x x x
xact_rollback x x x x x
blks_read x x x x x
blks_hit x x x x x
tup_returned x x x
tup_fetched x x x
tup_inserted x x x
tup_updated x x x
tup_deleted x x x
conflicts x x
temp_files x
temp_bytes x
deadlocks x
blk_read_time x
blk_write_time x
stats_reset* x x
* value ignored and therefore not recorded.
More information about the meaning of these metrics can be found in the PostgreSQL Documentation