Author Archives: Bobby

In my previous post I explained that setting db_writer_processes=1, dbwr_io_slaves=32 made a 2-3 times reduction in run time of my test of 15 concurrent updates. Further testing has shown that an even greater improvement – really 10 times – can … Continue reading →

I’m working on an HP-UX system that doesn’t have asynchronous I/O configured and I’m getting a bunch of “free buffer waits” which indicates that the DBWR processes are having trouble writing updated blocks from memory to disk fast enough.  Some … Continue reading →

I used this query to debug some updating issues on a table: select ss.DATAOBJ#, sn.END_INTERVAL_TIME, ss.DB_BLOCK_CHANGES_DELTA, ss.PHYSICAL_WRITES_DELTA from DBA_HIST_SEG_STAT ss, DBA_HIST_SNAPSHOT sn, DBA_HIST_SEG_STAT_OBJ so where so.OWNER=’MYUSER’ and so.OBJECT_NAME=’PLAN_TABLE’ and so.OBJECT_TYPE=’TABLE’ and ss.OBJ#=so.OBJ# and ss.DATAOBJ#=so.DATAOBJ# and ss.snap_id=sn.snap_id order by ss.snap_id,ss.DATAOBJ#; This … Continue reading →

You can use DBA_HIST_ACTIVE_SESS_HISTORY to show details about the PeopleSoft operator id (OPRID) and which part of the online application they were in.  I was just looking at a Query Manager issue and found that DBA_HIST_ACTIVE_SESS_HISTORY populated these three columns … Continue reading →

I attended John Beresniewicz’s Active Session History (ASH)  talk at Collaborate 13 on Monday.  One simple point from it was that he commonly sees queries of the ASH views that use the TIME_WAITED column incorrectly and result in incorrect results.  … Continue reading →

Well, I’m giving this talk related to Exadata at the Collaborate 13 usergroup conference on Monday.  I’ve spent a lot of time – probably too much time – preparing the slides and practicing the talk.  I first gave this talk … Continue reading →

Link to the latest version of my Exadata talk slides: zip Here are the details of my presentation time and place if you are going to Collaborate 13 in Denver: Session title: Exadata Distinctives Room: Mile High Ballroom 1C Date … Continue reading →

The central point of my Exadata presentation is that data flows from the disks and into and out of memory caches in a different way on Exadata when using a Smart Scan than in non-Exadata Oracle databases.  An interesting consequence … Continue reading →

I just wanted to double check something on my Exadata slides.  I think I had checked this before but became unsure if something I was saying was true, namely that when you run a normal non-smart scan query on Exadata … Continue reading →

I ran into a case today where I had tuned a query by putting a cardinality hint into a view, but the optimizer changed the plan anyway by overriding the cardinality hint with cardinality feedback.  So, I found out how … Continue reading →