On 3 September 2016 at 04:25, Claudio Freire <klaussfre...@gmail.com> wrote: > The attached patch allows setting maintainance_work_mem or > autovacuum_work_mem higher than 1GB (and be effective), by turning the > allocation of the dead_tuples into a huge allocation. > > This results in fewer index scans for heavily bloated tables, and > could be a lifesaver in many situations (in particular, the situation > I'm living right now in production, where we don't have enough room > for a vacuum full, and have just deleted 75% of a table to make room > but have to rely on regular lazy vacuum to free the space).
This part looks fine. I'm inclined to commit the attached patch soon. > The patch also makes vacuum free the dead_tuples before starting > truncation. It didn't seem necessary to hold onto it beyond that > point, and it might help give the OS more cache, especially if work > mem is configured very high to avoid multiple index scans. How long does that part ever take? Is there any substantial gain from this? Lets discuss that as a potential second patch. > Tested with pgbench scale 4000 after deleting the whole > pgbench_accounts table, seemed to work fine. -- Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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