Murthy Nunna <mnunna(at)fnal(dot)gov> writes:
> I did pg_dump of a ~20TB database followed by pg_restore. I find simple queries like select count(*) running slow. I did a select count(*) on all tables before pg_dump which took ~4 hours. After pg_restore, same thing took 32 hours.
My bet is that that was setting commit hint bits, and hence incurring
a lot of writes. If the data is reasonably stable that's a one-time
expense.
regards, tom lane