Re: Pg_upgrade speed for many tables

On Mon, Nov  5, 2012 at 03:08:17PM -0500, Bruce Momjian wrote:
> Magnus reported that a customer with a million tables was finding
> pg_upgrade slow.  I had never considered many table to be a problem, but
> decided to test it.  I created a database with 2k tables like this:
> 
> 	CREATE TABLE test1990 (x SERIAL);
> 
> Running the git version of pg_upgrade on that took 203 seconds.  Using
> synchronous_commit=off dropped the time to 78 seconds.  This was tested
> on magnetic disks with a write-through cache.  (No change on an SSD with
> a super-capacitor.)
> 
> I don't see anything unsafe about having pg_upgrade use
> synchronous_commit=off.  I could set it just for the pg_dump reload, but
> it seems safe to just use it always.  We don't write to the old cluster,
> and if pg_upgrade fails, you have to re-initdb the new cluster anyway.
> 
> Patch attached.  I think it should be applied to 9.2 as well.

Modified patch attached and applied to head and 9.2.  I decided to use
synchronous_commit=off only on the new cluster, just in case we ever do
make a modification of the old cluster.

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +