On Fri, Mar 31, 2017 at 8:17 PM, Robert Haas <robertmh...@gmail.com> wrote:
> Starting a new thread about this to get more visibility. > > Despite the extensive work that has been done on hash indexes this > release, we have thus far not made any change to the on-disk format > that is not nominally backward-compatible. Commit > 293e24e507838733aba4748b514536af2d39d7f2 did make a change for new > hash indexes, but included backward-compatibility code so that old > indexes would continue to work. However, I'd like to also commit > Mithun Cy's patch to expand hash indexes more gradually -- latest > version in http://postgr.es/m/CAD__OujD-iBxm91ZcqziaYftWqJxnFqgMv361V9 > zke83s6i...@mail.gmail.com > -- and that's not backward-compatible. > > It would be possible to write code to convert the old metapage format > to the new metapage format introduced by that patch, and it wouldn't > be very hard, but I think it would be better to NOT do that, and > instead force everybody upgrading to v10 to rebuild all of their hash > indexes. If we don't do that, then we'll never know whether > instances of hash index corruption reported against v10 or higher are > caused by defects in the new code, because there's always the chance > that the hash index could have been built on a pre-v10 version, got > corrupted because of the lack of WAL-logging, and then been brought up > to v10+ via pg_upgrade. Forcing a reindex in v10 kills three birds > with one stone: > > - No old, not logged, possibly corrupt hash indexes floating around > after an upgrade to v10. > - Can remove the backward-compatibility code added by > 293e24e507838733aba4748b514536af2d39d7f2 instead of keeping it around > forever. > - No need to worry about doing an in-place upgrade of the metapage for > the above-mentioned patch. > > Thoughts? > Given the state of hash indexes in <= 9.6, I think this is a reasonable tradeoff. Most people won't be using them at all today. Those that do will have to "pay" with a REINDEX on upgrade. I think the benefits definitely outweigh the cost. So +1 for doing it. -- Magnus Hagander Me: http://www.hagander.net/ Work: http://www.redpill-linpro.com/
