(sending again, forgot to cc hackers, sorry for the duplicate) Hi,
I'm trying to use the custom scan API to replace code that currently does everything via hooks and isn't safe against copyObject() (Yes, that's not a grand plan). To me dealing with CustomScan->custom_private seems to be extraordinarily painful when dealing with nontrivial data structures. And such aren't all that unlikely when dealing with a custom scan over something more complex. Now, custom scans likely modeled private data after FDWs. But it's already rather painful there (in fact it's the one thing I heard people complain about repeatedly besides the inability to push down operations). Just look at the ugly hangups postgres_fdw goes through to pass data around - storing it in lists with indexes determining the content and such. That kinda somewhat works if you only integers and such need to be stored, but if you have more complex data it really is a PITA. The best alternatives I found are a) to serialize data into a string, base64 or so. b) use a Const node over a bytea datum. It seems rather absurd having to go through deserialization at every execution. Since we already have CustomScan->methods, it seems to be rather reasonable to have a CopyCustomScan callback and let it do the copying of the private data if present? Or possibly of the whole node, which'd allow to embed it into a bigger node? I looked at pg-strom and it seems to go through rather ugly procedures to deal with the problem: https://github.com/pg-strom/devel/blob/master/src/gpujoin.c form_gpujoin_info/deform_gpujoin_info. What's the advantage of the current model? Greetings, Andres Freund -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
