Re: computational model of transactions

"Marshall" <marshall.spight_at_gmail.com> wrote in message news:1154712384.843649.326550_at_b28g2000cwb.googlegroups.com...
> Erwin wrote:
> >
> > AFAICT, MVCC is only safe to use in transactions that don't update
> > anything, i.e. transactions that do *nothing but reads*.
>
> Um, if we are doing nothing but reads, we don't need any concurrency
> controls at all. Everything can read everything all the time safely, if
> there are no writes going on. So it kind of seems like above you're
> saying MVCC is a no-op.
>
>
> Marshall
>

A slight correction here, Marshall.

I believe what Erwin is describing is a situation where there are multiple transactions running concurrently, and some of them are read-write while others are read-only. MVCC can be used to isolate the read only transactions from the updaters, while some other mechanism (locking?) can be used to protect the updaters from each other.

I may be reading the above into what Erwin wrote, because that's what I'm familiar with: a DB server where the reader can be fed consistent data from superceded versions of data, while updaters queue up for certain resources. Received on Sat Aug 05 2006 - 05:30:49 CDT