Understanding Oracle Histograms

Histograms are a feature of the Cost Based Optimizer (CBO) that helps to know the data distribution in a column. Histograms should be created in columns with highly skew data and are included in the filter clause (WHERE) of a SQL statement.Histograms play a very important role in the creation of the execution plan and… Continue reading Understanding Oracle Histograms

MRP0: Background Media Recovery terminated with error 1237

Some days back checking an Oracle physical standby database found that the DB was some hours back than the primary database.alter session set nls_date_format='DD-MM-yyyy HH24:MI:SS';show parameter destselect thread#,max(sequence#) from gv$log_history group by thread#;select (a.amct-b.bmct)*24 "Hours Standby is Behind: " from (select max(completion_time) amct from v$archived_log) a, (select max(completion_time) bmct from v$archived_log where applied='YES') b;Hours Standby… Continue reading MRP0: Background Media Recovery terminated with error 1237

Testing user calls

In the performance tuning world specially talking about Response Time Analysis (RTA), user calls is often used as a workload metric; however this instance statistic was not yet completely clear.When this metric is incremented?, How this metric is instrumented?, Why sometimes user calls is less with the same SQL statement?; these were some questions rounding… Continue reading Testing user calls