Обсуждение: Question regarding clock-sweep
Tom, 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? Oh, and incidentally, can I use the same database files for 8.0.2 and 8.1cvs 3/10/05? -- Josh Berkus Aglio Database Solutions San Francisco
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