Re: POC: make mxidoff 64 bits

Hi Maxim Orlov
Thank you so much for your tireless work on this. Increasing the WAL
size by a few bytes should have very little impact with today's disk
performance(Logical replication of this feature wal log is also increased a
lot, logical replication is a milestone new feature, and the community has
been improving the logical replication of functions),I believe removing
troubled postgresql Transaction ID Wraparound was also a milestone new
feature adding a few bytes is worth it!

Best regards

On Tue, 23 Apr 2024 at 17:37, Heikki Linnakangas <hlinnaka(at)iki(dot)fi> wrote:

> On 23/04/2024 11:23, Maxim Orlov wrote:
> > PROPOSAL
> > Make multixact offsets 64 bit.
>
> +1, this is a good next step and useful regardless of 64-bit XIDs.
>
> > @@ -156,7 +148,7 @@
> > ((uint32) ((0xFFFFFFFF % MULTIXACT_MEMBERS_PER_PAGE) + 1))
> >
> > /* page in which a member is to be found */
> > -#define MXOffsetToMemberPage(xid) ((xid) / (TransactionId)
> MULTIXACT_MEMBERS_PER_PAGE)
> > +#define MXOffsetToMemberPage(xid) ((xid) / (MultiXactOffset)
> MULTIXACT_MEMBERS_PER_PAGE)
> > #define MXOffsetToMemberSegment(xid) (MXOffsetToMemberPage(xid) /
> SLRU_PAGES_PER_SEGMENT)
> >
> > /* Location (byte offset within page) of flag word for a given member */
>
> This is really a bug fix. It didn't matter when TransactionId and
> MultiXactOffset were both typedefs of uint32, but it was always wrong.
> The argument name 'xid' is also misleading.
>
> I think there are some more like that, MXOffsetToFlagsBitShift for example.
>
> --
> Heikki Linnakangas
> Neon (https://neon.tech)
>
>
>
>