Re: Simplifying wal_sync_method

On 2005-08-10, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Andrew - Supernews <andrew+nonews(at)supernews(dot)com> writes:
>>> If a SCSI drive reports write complete when it hasn't actually put the
>>> bits on the platter yet, then it's simply broken.
>
>> I guess you haven't read the spec much, then.
>
> [ shrug... ] I have seen that spec before: I was making a living by
> implementing SCSI device drivers in the mid-80's. I think that anyone
> who uses WCE in place of tagged command queueing is not someone whose
> code I would care to rely on for mission-critical applications. TCQ
> is a design that just works; WCE is someone's attempt to emulate all
> the worst features of IDE.

1) Tag queueing and WCE are orthogonal concepts. It's not a question of
using one "in place of" the other. My comment was that my recent
observation of actual SCSI drives is that WCE is enabled by default and
as such _will_ be used unless either you disable it manually, or the host
OS does so.

2) What OSes in common use adapt to the WCE setting, either by turning it
off, or using FUA or issuing SYNCHRONIZE CACHE commands? Since it is
entirely transparent to the host OS, I do not believe any are, though it
looks like very recent Linux development is moving in this direction.

--
Andrew, Supernews
http://www.supernews.com - individual and corporate NNTP services