On 08/22/2011 05:54 PM, Jim Nasby wrote:
I know folks have talked about progress, but I haven't seen anything specific... could you add info about what table/index vacuum is working on, and how far along it is? I realize that's not very close to an actual % completion, but it's far better than what we have right now.
Due to complaints about the mechanism the first version used to inform the user of the progress, I'm yanking that from the next patch altogether. The goal for now is to get a good report into the logs, and then maybe that gets extended later with a progress report. (All of the proposed alternate mechanisms are way more complicated than anything I have time to do right now)
FWIW, the number I end up caring about isn't so much write traffic as read. Thanks to a good amount of battery-backed write cache (and possibly some iSCSI misconfiguration), our writes are generally much cheaper than our reads.
VACUUM can't really know its true read rate from what's inside the database. I can add a summary of the accumulated read amounts into the logs, in more useful figures than what is provided so far, which is better than nothing. But those will be kind of deceptive, which is one reason I wasn't so focused on them yet. If the relation is largely in the OS cache, but not the PostgreSQL one, the summary can show a read rate even when that isn't actually doing any reads at all. That was exactly the case in the sample data I posted. VACUUM thought it was reading anywhere from 2.5 to 6MB/s. But at the OS level, it was actually reading zero bytes, since the whole thing was in cache already.
What you actually want is a count of the accumulated read counters at the OS level. I've recently figured out how to track those, too, but that code is something that lives outside the database. If this is something useful to you, I think you're about to sign up to be my next beta tester for that program.
-- Greg Smith 2ndQuadrant US g...@2ndquadrant.com Baltimore, MD PostgreSQL Training, Services, and 24x7 Support www.2ndQuadrant.us -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
