On Fri, Aug 19, 2022 at 9:40 AM Tom Lane <t...@sss.pgh.pa.us> wrote: > Yeah, we use "blocks" and "pages" interchangeably, which is something > I don't feel a need to change; but evidently the OP didn't realize that. > This is a job for the glossary, perhaps?
I think that they're synonyms that can often (but not always) be used interchangeably. I *think* that this understanding is shared by other people, though I should check. Here goes: To me, "block" emphasizes on-disk/relfilenode storage. Something that exists at a particular physical offset in a particular file (a BlockNumber + relfilenode). On the other hand, the term "page" emphasizes the in-memory format, and the indirection provided by the bufpage.c slotted page format (i.e. line pointer array indirection). This line pointer indirection is really central to lots of important things, including (just for example) our "physiological" approach to WAL logging -- WAL records describe changes in a way that is physical to a block, logical within a page. Most users don't need to care about these distinctions, but hackers might find the nuance of it quite useful. It bleeds into a lot of things, and is quite easy to take for granted -- which might actually cost you. -- Peter Geoghegan
