On Tue, Aug 3, 2021 at 3:32 PM Andres Freund <and...@anarazel.de> wrote: > I am now wondering if what we're talking about here would best be thought of > not as a variable width integer type, but a variable-width encoding for all > pass-by-value types. > > Leaving on-disk compatibility aside (:)), ISTM that we by default could use > the following heuristic to decide how to encode pass-by-value types: If it's a > leading fixed-width NOT NULL type, store it in fixed-length > encoding. Otherwise use a variable-length encoding.
This is pretty integer-centric, though. If your pass-by-value type is storing timestamps, for example, they're not likely to be especially close to zero. Since a 64-bit address is pretty big, perhaps they're still close enough to zero that this will work out to a win, but I don't know, that seems a bit cheesy. I grant that it could work out to a win -- pass-by-value data types whose distribution is very different from what's typical for integers, or for that matter columns full of integers that all happen to be toward the extreme values the data type can store, are probably not that common. I just don't really like making such assumptions on a system-wide basis (as opposed to a per-datatype basis where it's easier to reason about the consequences). -- Robert Haas EDB: http://www.enterprisedb.com
