Re: Re: [COMMITTERS] pgsql: Avoid extra locks in GetSnapshotData if old_snapshot_threshold <

On Wed, Apr 13, 2016 at 11:18 AM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> I think generally the only platform of concern wrt is arm (< armv8),
> which doesn't have 64bit atomicity and doesn't have
> single-copy-atomicity for 8 byte values either (C.f.
> https://wiki.postgresql.org/wiki/Atomics).

That page is sort of confusing, because it says that platform has
those things but then says ***, which is footnoted to mean "linux
kernel emulation available", but it's not too clear whether that
applies to all atomics or just 8-byte atomics. The operator
precedence of / (used as a separator) vs. footnotes is not stated.
It's also not clear what "linux kernel emulation available" actually
means. Should we think of those things being fast, or slow?

At any rate, I do actually have a Raspberry Pi 2 here so if we ever
commit a patch that might suck without real 64-bit atomics we might be
able to actuall test whether it does or not. But as you say, no such
patch is being proposed at the moment.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company