On Tue, Jul 14, 2015 at 4:47 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > I think this ties into my core unhappiness with the customscan stuff, > which is that I don't believe it's *possible* to do anything of very > great interest with it. I think anything really useful will require > core code modifications and/or hooks that don't exist now. So a finger > exercise like ctidscan, even though it might have some marginal use, > doesn't do much to alleviate that concern. It certainly doesn't seem > like it's a suitable placeholder proving that we aren't breaking any > actual use cases for the feature.
Both you and Andres have articulated the concern that CustomScan isn't actually useful, but I still don't really understand why not. KaiGai has got working code (under a GPL license) that shows that it can be used for what he calls GpuScan and GpuJoin, and the speedups are actually pretty cool if you happen to have the right sort of query to take advantage of it. That code may be buggy and the license precludes us using it anyway, but FWICT it does seem to work. I'd be entirely amenable to improving the infrastructure such that it could be used for a broader array of purposes, and I'm also amenable to adding more hooks if we need more hooks to make it useful, but I'm not clear at all on what you think is missing. I'm curious, for example, whether CustomScan would have been sufficient to build TABLESAMPLE, and if not, why not. Obviously the syntax has to be in core, but why couldn't the syntax just call an extension-provided callback that returns a custom scan, instead of having a node just for TABLESAMPLE? -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers