Re: Support Parallel Query Execution in Executor

Josh Berkus <josh(at)agliodbs(dot)com> writes:
> Basically reading a large table off disk does this:

> read some table while not processing
> process in cpu while not reading
> read some more table while not processing
> process some more in cpu while not reading
> etc.
> resulting in an I/O througput graph that looks like:

> * * *
> * * * * * *
> * * * * * *
> * * * *

Interesting ...

> The really annoying part about this, for me personally, is that the peaks
> are significantly faster than comparable commercial DBMSes ... but our
> average is far less. So even on a single seq scan, parallel query
> execution would make a significant difference in performance, possibly as
> much as +75% on seq scans of large tables.

... but I'm failing to follow where it says that parallel processing
will fix that. All I can foresee in that direction is extra data
transfer costs, bought at the price of portability and locking headaches.

regards, tom lane