Re: pg_dump is O(N) in DB table count N even if dumping only one table

On Mon, Jun 10, 2013 at 2:08 PM, Andres Freund <andres(at)2ndquadrant(dot)com>wrote:

> On 2013-06-10 13:28:32 +0000, Gunnlaugur Thor Briem wrote:
> > The three queries taking O(N) time are listed below. AFAICT each of these
>
> Which of those queries take how long in your case?
>

They were as follows:

duration: 27770.917 ms statement: SELECT c.tableoid, c.oid, c.relname, ...
duration: 28133.407 ms statement: SELECT tableoid, oid, typname, ...
duration: 55751.996 ms statement: SELECT classid, objid, refclassid, ...

However, that was running pg_dump remotely over a slow network, and that
may exaggerate durations since it's a bunch of data. So I ran this again
locally on the production server:

duration: 16012.518 ms statement: SELECT c.tableoid, c.oid, c.relname, ...
duration: 16516.708 ms statement: SELECT tableoid, oid, typname, ...
duration: 13400.694 ms statement: SELECT classid, objid, refclassid, ...

Duration decrease is probably *not* significantly due to a warmer cache,
because I had two runs over the slow network and their durations were
similar (actually longer the second time).

Gulli