Re: limiting hint bit I/O

On Jan 18, 2011, at 8:24 AM, Merlin Moncure wrote:
> a few weeks back I hacked an experimental patch that removed the hint
> bit action completely.  the results were very premature and/or
> incorrect, but my initial findings suggested that hint bits might not
> be worth the cost from performance standpoint.  i'd like to see some
> more investigation in this direction before going with a complex
> application mechanism (although that would be beneficial vs the status
> quo).

If you're not finding much benefit to hint bits, that's *very* interesting. Everything I outlined certainly looks like a pretty damn expensive code path; it's really surprising that hint bits don't help.

I think it would be very valuable to profile the cost of the different code paths involved in the HeapTupleSatisfies* functions, even if the workload is just pgBench.

> an ideal testing environment to compare would be a mature database
> (full clog) with some verifiable performance tests and a mixed
> olap/oltp workload.

We're working on setting such a framework up. Unfortunately it will only be 8.3 to start, but we hope to be on 9.0 soon.
--
Jim C. Nasby, Database Architect                   jim@nasby.net
512.569.9461 (cell)                         http://jim.nasby.net