On 4/3/2025 22:23, Robert Haas wrote:
On Tue, Mar 4, 2025 at 1:53 PM Jeff Davis <pg...@j-davis.com> wrote:
I don't expect there to be zillions of extensions that only add new and
exciting explain options. Instead, it seems more likely that all
TableAM and CustomScan extensions will have 1-3 new explain options,
and that some of those might collide. For example, several may have a
EXPLAIN(PUSHDOWN) option that explains what work is being pushed down
into the TableAM/CustomScan.
In that case it's not even clear to me that a collision is a problem.
Would you really only want pushdown information from extension A, and
be upset that it also emits pushdown information from extension B?
Maybe we should just allow multiple extensions to use the same option
name?
...
Actually, I don't think custom scans or table AMs are the design
center for this feature. Keep in mind that, for a custom scan, we
already have ExplainCustomScan as part of CustomScanState->methods. We
don't currently have anything similar for table AMs, and you could
work around that with these hooks, by checking every node to see
whether it's a scan node and if so whether it scans a relation that
matches your table AM, but it would probably be better to have a
method for it, similar to what we have for CustomScan, if this is
something people want to do. It would be more efficient and require
less code.
+1. In my experience, ExplainCustomScan has always been enough for the
CustomScan node.
As for extensions collision - for now, it would be better to treat
extensions as independent actors, suggesting that the developer,
designing a software solution based on an extensions' constellation,
will arrange their behaviour during development.
For instance, if your library exports a function or variable, adding a
prefix is essential to prevent overlapping functions when another
library is loaded.
I recall that Yurii Rashkovskii is a proponent of using multiple
extensions within a single installation. Perhaps he has insights on this
topic?
--
regards, Andrei Lepikhov
