On Tue, Jan 20, 2015 at 5:42 PM, Robert Haas <robertmh...@gmail.com> wrote: > On Tue, Jan 20, 2015 at 8:39 PM, Peter Geoghegan <p...@heroku.com> wrote: >> On Tue, Jan 20, 2015 at 5:32 PM, Robert Haas <robertmh...@gmail.com> wrote: >>> I was assuming we were going to fix this by undoing the abbreviation >>> (as in the abort case) when we spill to disk, and not bothering with >>> it thereafter. >> >> The spill-to-disk case is at least as compelling at the internal sort >> case. The overhead of comparisons is much higher for tapesort. > > First, we need to unbreak this. Then, we can look at optimizing it. > The latter task will require performance testing.
I don't see that any alternative isn't a performance trade-off. My patch accomplishes unbreaking this. I agree that it needs still needs review from that perspective, but it doesn't seem any worse than any other alternative. Would you prefer it if the spill-to-disk case aborted in the style of low entropy keys? That doesn't seem significantly safer than this, and it certainly not acceptable from a performance perspective. -- Peter Geoghegan -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
