Re: First draft of the PG 15 release notes

On Thu, 19 May 2022 at 14:41, Amit Langote <amitlangote09(at)gmail(dot)com> wrote:
> Though a bit late given beta is now wrapped, I have another partition
> item wording improvement suggestion:
>
> -Previously, a partitioned table with any LIST partition containing
> multiple values could not be used for ordered partition scans. Now
> only non-pruned LIST partitions are checked. This also helps with
> -partitioned tables with DEFAULT partitions.
>
> +Previously, an ordered partition scan would not be considered for a
> LIST-partitioned table with any partition containing multiple values,
> nor for partitioned tables with DEFAULT partition.

I think your proposed wording does not really improve things. The
"Now only non-pruned LIST partitions are checked" is important and I
think Bruce did the right thing to mention that. Prior to this change,
ordered scans were not possible if there was a DEFAULT or if any LIST
partition allowed >1 value. Now, if the default partition is pruned
and there are no non-pruned partitions that allow Datum values that
are inter-mixed with ones from another non-pruned partition, then an
ordered scan can be performed.

For example, non-pruned partition a allows IN(1,3), and non-pruned
partition b allows IN(2,4), we cannot do the ordered scan. With
IN(1,2), IN(3,4), we can.

David