On 7 July 2013 14:24, Simon Riggs <si...@2ndquadrant.com> wrote: > On 3 January 2012 18:42, Tom Lane <t...@sss.pgh.pa.us> wrote: >> I wrote: >>>> Another point that requires some thought is that switching SnapshotNow >>>> to be MVCC-based will presumably result in a noticeable increase in each >>>> backend's rate of wanting to acquire snapshots. >> >> BTW, I wonder if this couldn't be ameliorated by establishing some >> ground rules about how up-to-date a snapshot really needs to be. >> Arguably, it should be okay for successive SnapshotNow scans to use the >> same snapshot as long as we have not acquired a new lock in between. >> If not, reusing an old snap doesn't introduce any race condition that >> wasn't there already. > > Now that has been implemented using the above design, we can resubmit > the lock level reduction patch, with thanks to Robert. > > Submitted patch passes original complaint/benchmark. > > Changes > * various forms of ALTER TABLE, notably ADD constraint and VALIDATE > * CREATE TRIGGER > > One minor coirrections to earlier thinking with respect to toast > tables. That might be later relaxed. > > Full tests including proof of lock level reductions, plus docs.
Rebased to v14 -- Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services
reduce_lock_levels.v14.patch
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