On 16 January 2012 00:59, Jeff Janes <jeff.janes@gmail.com> wrote:
> I think it would be better to pre-deduct the tape overhead amount we
> will need if we decide to switch to tape sort from the availMem before
> we even start reading (and then add it back if we do indeed make that
> switch). That way we wouldn't over-run the memory in the first place.
> However, that would cause apparent regressions in which sorts that
> previously fit into maintenance_work_mem no longer do. Boosting
> maintenance_work_mem to a level that was actually being used
> previously would fix those regressions, but pointing out that the
> previous behavior was not optimal doesn't change the fact that people
> are used to it and perhaps tuned to it. So the attached patch seems
> more backwards-friendly.
Hmm. Are people really setting maintenance_work_mem such that it is
exactly large enough to quicksort when building an index in one case
but not another? Is the difference large enough to warrant avoiding
pre-deduction?
--
Peter Geoghegan http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training and Services
