On Mon, 15 Apr 2024 at 19:36, Robert Haas <robertmh...@gmail.com> wrote:
> On Sat, Apr 13, 2024 at 5:28 AM Alexander Korotkov <aekorot...@gmail.com> > wrote: > > Yes, I think so. Table AM API deals with TIDs and block numbers, but > > doesn't force on what they actually mean. For example, in ZedStore > > [1], data is stored on per-column B-trees, where TID used in table AM > > is just a logical key of that B-trees. Similarly, blockNumber is a > > range for B-trees. > > > > c6fc50cb4028 and 041b96802ef are putting to acquire_sample_rows() an > > assumption that we are sampling physical blocks as they are stored in > > data files. That couldn't anymore be some "logical" block numbers > > with meaning only table AM implementation knows. That was pointed out > > by Andres [2]. I'm not sure if ZedStore is alive, but there could be > > other table AM implementations like this, or other implementations in > > development, etc. Anyway, I don't feel good about narrowing the API, > > which is there from pg12. > > I spent some time looking at this. I think it's valid to complain > about the tighter coupling, but c6fc50cb4028 is there starting in v14, > so I don't think I understand why the situation after 041b96802ef is > materially worse than what we've had for the last few releases. I > think it is worse in the sense that, before, you could dodge the > problem without defining USE_PREFETCH, and now you can't, but I don't > think we can regard nonphysical block numbers as a supported scenario > on that basis. > > But maybe I'm not correctly understanding the situation? > Hi, Robert! In my understanding, the downside of 041b96802ef is bringing read_stream* things from being heap-only-related up to the level of acquire_sample_rows() that is not supposed to be tied to heap. And changing *_analyze_next_block() function signature to use ReadStream explicitly in the signature. Regards, Pavel.
