Re: POC: make mxidoff 64 bits

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)