On Fri, 2005-02-25 at 13:38 +0000, Simon Riggs wrote:
> On Fri, 2005-02-25 at 00:34 -0800, Jeff Davis wrote:
> > I had an idea that might improve parallel seqscans on the same relation.
> > If you have lots of concurrent seqscans going on a large relation, the
> > cache hit ratio is very low. But, if the seqscans are concurrent on the
> > same relation, there may be something to gain by starting a seqscan near
> > the page being accessed by an already-in-progress seqscan, and wrapping
> > back around to that start location. That would make some use of the
> > shared buffers, which would otherwise just be cache pollution.
> This is cool and was on my list of would-like-to-implement features.
> It's usually known as Synchronised Scanning. AFAIK it is free of any
> patent restriction: it has already been implemented by both Teradata and
> > This is the first time I've really modified the PG source code to do
> > anything that looked promising, so this is more of a question than
> > anything else. Is it promising? Is this a potentially good approach? I'm
> > happy to post more test data and more documentation, and I'd also be
> > happy to bring the code to production quality.
> I'll be happy to help you do this, at least for design and code review.
> I'll come back later with more detailed comments on your thoughts so
Good to hear. I'll clean up the code and document some more tests. Three
questions come to mind right now:
(1) Do we care about reverse scans being done with synchronized
scanning? If so, is there a good way to know in advance whether it is
going to be a forward or reverse scan (i.e. before heap_getnext())?
(2) Where is the appropriate place to put the page location of an
in-progress scan? Are there other pieces of shared memory that aren't
disk buffers that I should be making use of?
> > However, before I spend
> > too much more time on that, I'd like to get a general response from a
> > 3rd party to let me know if I'm off base.
> Third party?
A 2nd party? Anyone else? That was a typo :)
In response to
pgsql-hackers by date
|Next:||From: Josh Berkus||Date: 2005-02-25 17:41:45|
|Subject: Re: Development Plans|
|Previous:||From: Marc G. Fournier||Date: 2005-02-25 17:27:09|
|Subject: Re: [HACKERS] Interesting NetBSD annual report|