This is a very busy system, lots happened during that 10 hours. I don't have session-specific stats, so the best I could do was look at some AWR stats over a 30-minute window - but this particular instance wasn't very busy, so luckily these statistics mainly reflect this query. I looked at the very last 30 minutes since I figured it would be the worst-performing time. This SQL statement accounted for 90% of buffer gets on the instance during the snapshot. Here are the statistics Jonathan mentioned: AWR snap coveres 30:04 == 1804s Total Logical Reads: 10,823.1/s SQL 8suhywrkmpj5c: 17,617,831 gets ... 9,765 gets/sec TOTAL PER-SECOND STATISTIC 148,983 82.61 CR blocks created 15,406,266 8,542.71 consistent gets - examination 168,222 93.28 data blocks consistent reads - undo records applied 21,173 11.74 db block gets 160 0.09 transaction tables consistent read rollbacks 7,929,413 4,396.82 transaction tables consistent reads - undo records applied 1,379,540 764.95 undo change vector size I'm not an expert on this... does this say that, per second: - the query is only actually processing 11 data blocks - it's applying 8.5 thousand undo records to get them - this requires 9.7 thousand actual block accesses What other stats would be interesting? Am I reading these statistics correctly? Any further observations that can be made? -Jeremy -- http://www.ardentperf.com +1 312-725-9249 Jeremy Schneider Chicago On 11/17/2011 08:20 AM, Jonathan Lewis wrote: > Jeremy, > > How much other activity was going on in the 10 hours ? > > Before checking anything else I would look at the session stats (or instance > activity stats if you don't have session stats) for undo application: > data blocks consistent reads - undo records applied > CR blocks created > and the two relating to transaction table consistent reads. > > Each "undo record applied" will increment "consistent gets - examination". > > There are a couple of related observations here: > http://jonathanlewis.wordpress.com/2011/05/08/consistent-gets-3/ > > If you've got the AWR or statspack reports or the 10 hours you could check > these > figures hour by hour to see if they increase over time (a classic problem > with > long running queries is that the longer they take to run the more work they > do > generating constistent read copies, which makes them take longer to run, > which > ...) > > > Regards > > Jonathan Lewis > http://jonathanlewis.wordpress.com > > > ----- Original Message ----- > From: "Jeremy Schneider" <jeremy.schneider@xxxxxxxxxxxxxx> > To: <oracle-l@xxxxxxxxxxxxx> > Sent: Thursday, November 17, 2011 11:34 AM > Subject: index with very high LIO > > > Anyone have ideas why an index with blevel 3 is averaging 13 LIOs per > lookup/row? I'm working on the query below, which ran for about 10 > hours - the majority of which was spent doign 13 logical IOs per row in > this index. (BT_TWO_VARCHAR2_INDEX below... 121M buffers / 8792K starts > = 13 IOs per start) Performance on this query has been degrading > rapidly over the past month or two. > > -- > //www.freelists.org/webpage/oracle-l > > > -- //www.freelists.org/webpage/oracle-l