Re: pg_preadv() and pg_pwritev()

Thomas Munro <thomas(dot)munro(at)gmail(dot)com> writes:
> OK, here's a patch to zero-fill fresh WAL segments with pwritev().
> I'm drawing a blank on trivial candidate uses for preadv(), without
> infrastructure from later patches.

This looks OK to me. I tried it on prairiedog (has writev and
pwrite but not pwritev) as well as gaur (has only writev).
They seem happy.

One minor thought is that in

+ struct iovec iov[Min(IOV_MAX, 1024)]; /* cap stack space */

it seems like pretty much every use of IOV_MAX would want some
similar cap. Should we centralize that idea with, say,

#define PG_IOV_MAX Min(IOV_MAX, 1024)

? Or will the plausible cap vary across uses?

regards, tom lane