Re: pg_preadv() and pg_pwritev()

Thomas Munro <thomas.munro@gmail.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