On Wed, Feb 09, 2005 at 03:38:32PM -0700, Ed L. wrote: > On Wednesday February 9 2005 3:13, Martijn van Oosterhout wrote: > > > > In general, the EXPLAIN ANALYZE output follows the planner > > output as close as possible. If you look at the original query > > posted, it showed an Index Scan costing 4.63..4.63 which means > > the index scan is taking (on average) 4.63ms to return 1 row! > > If it displayed as 4000 or something it would be a lot less > > clear what was going on. > > > > Hope this helps, > > Both replies help very much, thanks. Regarding 4.63ms to return > a row, I know I/O speeds vary widely depending on conditions and > hardware, but what would you say is a "red flag" value for the > actual time to retrieve a row. I see that for most of the other > times in this example, 0.01ms to 0.10ms is not unusual.
That number 4.63ms is way out. Especially considering this is an *average* over 1000+ iterations which tells you something it very wrong with that step. Note, Index Scan can take a long time, it completely depends on how many rows it returns. Also, if there is an additional filter on the index (someotherfield = 'x') it may take a while to return a single value. But for unique indexes on primary keys (which is what this appears to be) the times should hopefully be <1ms *average* (caching and load are imprtant factors). Hope this helps, -- Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/ > Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a > tool for doing 5% of the work and then sitting around waiting for someone > else to do the other 95% so you can sue them.
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