On Fri, Jul 11, 2025 at 5:01 AM Dominique Devienne <ddevie...@gmail.com> wrote:
> On Thu, Jul 10, 2025 at 7:11 PM Ron Johnson <ronljohnso...@gmail.com> > wrote: > > On Thu, Jul 10, 2025 at 12:26 PM Adrian Klaver < > adrian.kla...@aklaver.com> wrote: > >> On 7/10/25 04:48, Dominique Devienne wrote: > >> > Seems so logical to me, that these hashing functions were available > >> > are aggregates, I can't be the first one to think of that, can it? > >> > >> I've been on this list since late 2002 and I don't recall this ever > >> being brought up. Now it is entirely possible that age has dimmed my > >> recall abilities:) Though a quick search seems to confirm my memory. > > > > What even is an aggregate hash function? (I can imagine a few > possibilities, but don't want to assume.) > > Well, it's so obvious to me, I wonder if you're baiting me :) > > Any hasher/digest inits some internal state, processes bytes, > typically in "streaming-fashion" via successive byte spans (equivalent > to PostgreSQL's bytea), and yields a digest of various length at the > end. The current md5() and pgcrypto.digest() functions roll the x1 > init, xN process, and x1 finish into a single call, processing a > single bytea (or perhaps more intelligently for TOAST'ed values, the > 2K "rows" of those in streaming-fashion, hopefully. Can a dev > confirm?). As an aggregate, the processing is extended to all values > aggregated. So it "appends" all the fields into one (virtual) mega-structure and takes the hash on that. It's what I expected but wanted to verify. -- Death to <Redacted>, and butter sauce. Don't boil me, I'm still alive. <Redacted> lobster!
