Question regarding clock-sweep

Josh Berkus wrote:

Oh, and incidentally, can I use the same database files for 8.0.2 and 8.1cvs
3/10/05?

No.

-Neil

Josh Berkus <josh@agliodbs.com> writes:

Now that I'm beginning serious performance testing of clock-sweep, I
was going back through the lock discussion and am not sure what the
patch that actually went in 3 weeks ago consisted of. Is it
clock-sweep with a used/unused bit or a counter? How is it handling
seq scans?

It's clock-sweep with a counter. The counter increments on reference,
up to a small maximum value (BM_MAX_USAGE_COUNT in buf_internals.h),
and decrements when the clock hand passes over the buffer. I'd be
interested to see trials with different values of BM_MAX_USAGE_COUNT
... I made it 5 to start with but that was a WAG.

There's not any special smarts for seqscans, but the counter should
handle that.

Oh, and incidentally, can I use the same database files for 8.0.2 and 8.1cvs
3/10/05?

Sorry, we forced initdb already several times...

regards, tom lane

Tom, Neil,

Oh, and incidentally, can I use the same database files for 8.0.2 and
8.1cvs 3/10/05?

Sorry, we forced initdb already several times...

D'oh. Better see if I can get a second machine, then, since build of a 100G
DBT3 database takes 20 hours.

--
Josh Berkus
Aglio Database Solutions
San Francisco

Tom,

There's not any special smarts for seqscans, but the counter should
handle that.

So all pages start out with the same counter, except VACUUM tuples?

BTW, I found this paper on RDBMS memory management, which probably could have
saved us some weeks of discussion:
http://www.cs.usask.ca/~wew036/research/comprehensive.pdf

--
Josh Berkus
Aglio Database Solutions
San Francisco