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Right Deep, Left Deep and Bushy Joins in SQL

#555555;">What is right deep verses left deep? Good question. In join trees (not VST) the object on the left is acted upon first then the object on the right.  Below are left deep and right deep examples of the same query, showing

  • query text
  • join tree
  • join tree  modified to more clearly show actions
  • VST showing the same actions

#555555;">left_right_deep copy

CURSOR_SHARING : a picture is worth a 1000 words

Anyone who has been around Oracle performance over the years knows the grief that hard parsing SQL queries can cause on highly concurrent applications. The number one reason for hard parsing has been applications that don’t use bind variables. Without bind variables queries that would otherwise be shared get recompiled because their text is different and Oracle treats them as different queries. Oracle addressed this issue with a parameter called cursor_sharing. The parameter cursor_sharing has three values

  1. exact – the default
  2. similar – replace literals with bind variables, if a histogram keep literal in place
  3. force – replace literals with bind variables and use existing plan if it exists

Here is what the load looks like going from the default, exact, to the value force on a load of the same query but a query that doesn’t use bind variables:

Latency Heat Maps in SQL*Plus

This is so cool !

Screen Shot 2013-05-10 at 1.13.15 PM

The above is so cool.

The graphic shows the latency heatmap of “log file sync” on Oracle displayed in SQL*Plus! SQL*Plus ?! Yes, the age old text interface to Oracle showing colored graphics.

How did I do this? All I did was type

Latency heatmaps in D3 and Highcharts

See Brendan Gregg’s blog on how important and cool heatmaps can be for showing latency information and how average latency hides what is really going on:

Now if we want to create heatmap graphics, how can we do it? Two popular web methods for displaying graphics are Highcharts and D3. Two colleges of mine whipped up some quick examples in both Highcharts and D3 to show latency heatmaps and those two examples are shown below. The data in the charts is random just for the purposes of showing examples of these graphics in actions.