On 17 April 2018 at 20:09, Tom Lane <t...@sss.pgh.pa.us> wrote: > Alvaro Herrera <alvhe...@alvh.no-ip.org> writes: >> Andres was working on a radix tree structure to fix this problem, but >> that seems to be abandoned now, and it seems a major undertaking. While >> I agree that the proposed solution is a wart, it seems much better than >> no solution at all. Can we consider Fujii's proposal as a temporary >> measure until we fix shared buffers? I'm +1 on it myself. > > Once we've introduced a user-visible reloption it's going to be > practically impossible to get rid of it, so I'm -1. I'd much rather > see somebody put some effort into the radix-tree idea than introduce > a kluge that we'll be stuck with, and that doesn't even provide a > good user experience. Disabling vacuum truncation is *not* something > that I think we should recommend.
The truncation at the end of VACUUM takes an AccessExclusiveLock, which is already user visible. Using a radix tree won't alter that. ISTM the user might be interested in having the *lock* NOT happen, so I am +1 for the suggestion regardless of whether radix tree ever happens. The lock itself can be cancelled, so the user would also be interested in explicitly requesting a retry with a separate command/function. -- Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
