Possible Threading problem with -CURRENT / MySQL?

[Robert Watson]

On Tue, 15 Jun 2004, Daniel Eischen wrote:

> > My results were without HTT (It was FreeBSD-AMD64) I didn't have any memory 
> > options
> > or a mysql config file.
> > 
> > _This problem is directly related to a commit that was made between ~May 18 
> > and yesterday._
> 
> There was a subsystem lock(s) put in for networking a few days ago. 
> There were no changes to the threads library that would exhibit the
> behavior you are seeing. 

The candidate time range includes a number of big and relevant changes:

- mbuma becomes the mbuf allocator, which would affect heavy UNIX domain
  socket I/O since mbufs are used for that I/O on local mysql
  configurations.  Since general benchmarks I've seen suggest mbuma helps
  or has the same cost as the previous allocator, presumably it would be
  some special case regression.

- Coarse-grained locking was introduced in UNIX domain sockets, but Giant
  has not yet been removed.  This means we're paying an additional (and
  redundant) locking overhead without the benefits of the finer-grained
  locking model in the base tree.  I've set up a test box to look at the
  performance impact of that today to see if it resulted in a substantial
  regression.  I'd expect a few percent, but maybe it's worse and it would
  be good to know.

- There have been a number of amd64-related VM changes, optimizations,
  etc.  Maybe one didn't work out so well.  I don't have an amd64-box so
  I can't really reason about that too much just now.

If we can track down the date a little closer, that would help a lot. 
Even just adding a new data point for June 1 or June 7 would be helpful.

Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
robert at fledge.watson.org      Senior Research Scientist, McAfee Research