Oracle Scratchpad

April 12, 2007

Log File Switch

Filed under: Infrastructure,redo,Tuning — Jonathan Lewis @ 9:55 pm BST Apr 12,2007

A few days ago, I published a simple query you could run against v$log_history to show the time between log file switches.  So if you use this script and decide that your log file switches are happening at inappropriate intervals, what can you do ?

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April 9, 2007

Log Switching

Filed under: Performance,redo,Tuning — Jonathan Lewis @ 7:04 pm BST Apr 9,2007

Analytic function have all sorts of uses, and the lag() and lead() functions are among my favourites. I always like to remind people of the sorting overheads involved with analytic functions – but if you are prepared to accept the overhead the simplicity of comparing ‘current’ rows with ‘earlier’ or ‘later’ rows using lag() or lead() is a tremendous coding benefit.

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November 22, 2006

Tuning Updates

Filed under: Indexing,Infrastructure,Oracle,redo,Tuning,undo — Jonathan Lewis @ 8:45 pm BST Nov 22,2006

Consider the following update statement:

update
        /*+ index(t1 t1_n1) */
        t1
set
        n1 = 0,
        n2 = n2 + 1,
        status = 'X'
where
        n1 > 100
and     status = 'A'
;

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