Re: Tid scan improvements

Hi,

On 2019-03-18 22:35:05 +1300, David Rowley wrote:
> The commit message in 8586bf7ed mentions:
>
> > Subsequent commits will incrementally abstract table access
> > functionality to be routed through table access methods. That change
> > is too large to be reviewed & committed at once, so it'll be done
> > incrementally.
>
> and looking at [1] I see patch 0004 introduces some changes in
> nodeTidscan.c to call a new tableam API function named
> heapam_fetch_row_version. I see this function does have a ItemPointer
> argument, so I guess we must be keeping those as unique row
> identifiers in the API.

Right, we are. At least for now - there's some discussions around
allowing different format for TIDs, to allow things like index organized
tables, but that's for later.

> Patch 0001 does change the signature of heap_setscanlimits() (appears
> to be committed already), and then in 0010 the only code that calls
> heap_setscanlimits() (IndexBuildHeapRangeScan()) is moved and renamed
> to heapam_index_build_range_scan() and set to be called via the
> index_build_range_scan TableAmRoutine method. So it looks like out of
> that patch series nothing is there to allow you to access
> heap_setscanlimits() directly via the TableAmRoutine API, so perhaps
> for this to work heap_setscanlimits will need to be interfaced,
> however, I'm unsure if that'll violate any assumptions that Andres
> wants to keep out of the API...

I was kinda hoping to keep block numbers out of the "main" APIs, to
avoid assuming everything is BLCKSZ based. I don't have a particular
problem allowing an optional setscanlimits type callback that works with
block numbers. The planner could check its presence and just not build
tid range scans if not present. Alternatively a bespoke scan API for
tid range scans, like the later patches in the tableam series for
bitmap, sample, analyze scans, might be an option.

Greetings,

Andres Freund