On 10/11/07, Mike Klaas <[EMAIL PROTECTED]> wrote: > I'm seeing some interesting behaviour when doing benchmarks of query > and facet performance. Note that the query cache is disabled, and > the index is entirely in the OS disk cache. filterCache is fully > primed. > > Often when repeatedly measuring the same query, I'll see pretty > consistent results (within a few ms), but occasionally a run which is > almost exactly half the time: > > 240ms vs. 120ms: > > solr: DEBUG INFO: /select/ > facet=true&debugQuery=true&indent=on&start=0&q=www&facet.field=t&qt=dism > ax&version=2.2&rows=1 0 239 > solr: DEBUG INFO: /select/ > facet=true&debugQuery=true&indent=on&start=0&q=www&facet.field=t&qt=dism > ax&version=2.2&rows=1 0 237 > solr: DEBUG INFO: /select/ > facet=true&debugQuery=true&indent=on&start=0&q=www&facet.field=t&qt=dism > ax&version=2.2&rows=1 0 120 > solr: DEBUG INFO: /select/ > facet=true&debugQuery=true&indent=on&start=0&q=www&facet.field=t&qt=dism > ax&version=2.2&rows=1 0 120 > solr: DEBUG INFO: /select/ > facet=true&debugQuery=true&indent=on&start=0&q=www&facet.field=t&qt=dism > ax&version=2.2&rows=1 0 237 > solr: DEBUG INFO: /select/ > facet=true&debugQuery=true&indent=on&start=0&q=www&facet.field=t&qt=dism > ax&version=2.2&rows=1 0 238 > > The strange thing is that the execution time is halved across _all_ > parts of query processing: > > 101.0 total time > 1.0 setup/query parsing > 68.0 main query > 30.0 faceting > 0.0 pre fetch > 2.0 debug > > 201.0 total time > 1.0 setup/query parsing > 138.0 main query > 58.0 faceting > 0.0 pre fetch > 4.0 debug > > I can't really think of a plausible explanation. Fortuitous > instruction pipelining? It is hard to imagine a cause that wouldn't > exhibit consistency.
So the queries are one at a time, the index isn't changing, and nothing else happening in the system? It would be easier to explain an occasional long query than an occasional short one. It's weird how the granularity seems to be on the basis of a request (if the speedup sometimes happened half way through, then you'd get an average of the times). You could try -Xbatch to see if it's hotspot somehow, but I doubt that's it. -Yonik
