Re: Is monotonous xid8 is a right way to do?

Pavel Borisov <pashkin(dot)elfe(at)gmail(dot)com> writes:

> Hi hackers!
>
> Now we have two data types xid and xid8. The first one (xid) makes a
> numeric ring, and xid8 are monotonous.
>
> As per [1] "Unlike xid values, xid8 values increase strictly monotonically
> and cannot be reused in the lifetime of a database cluster."
>
> As a consequence of [1] xid8 can have min/max functions (committed in [2]),
> which xid can not have.
>
> When working on 64xid patch [3] we assume that even 64xid's technically can
> be wraparound-ed, although it's very much unlikely. I wonder what is
> expected to be with xid8 values at this (unlikely) 64xid wraparound?

Even if a cluster was consuming a million XIDs per second, it would take
over half a million years to wrap around the 64bit range. Is that really
something we should worry about?

ilmari(at)[local]:5432 ~=# select 2::numeric^64/10^9/3600/24/365;
┌──────────────────┐
│ ?column? │
├──────────────────┤
│ 584942.417355072 │
└──────────────────┘

- ilmari