Tag: AWR

Pro-active AWR Data Mining to Find Change in SQL Execution Plan

Many times we have been called for the poor performance of a database and it has been narrowed down to a  SQL statement. Subsequent analysis have shown that the execution plan has been changed and a wrong execution plan was being…

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Do AWR Reports Show the Whole Picture?

AWR report is a great source of aggregated information on top activities happening in our databases. I use data collected in AWR quite often, and obviously the easiest way of getting the data out from the AWR is by running the…

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Do you have enough Redo?

The question of whether a database has enough redo logs available is quite common. The documentation suggests to use FAST_START_MTTR_TARGET and V$INSTANCE_RECOVERY.OPTIMAL_LOGFILE_SIZE to identify “the optimal” redo log size based on the target recovery time. I’ve never used it and…

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Meaning of “Disk Reads” Values in DBA_HIST_SQLSTAT

This post relates to my previous writing on mining the AWR. I noticed that it’s very easy to misinterpret the DISK_READS_TOTAL and DISK_READS_DELTA columns in DBA_HIST_SQLSTAT. Let’s see what the documentation says: DISK_READS_TOTAL – Cumulative number of disk reads for…

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Trying Out S-ASH: Historical Performance Data for the Under-Licensed

I was recently playing with an Oracle XE database. The main benefit of Oracle XE is that it can be used free of charge.

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