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Tuesday, March 8, 2011

How to utilize AWR beyond what grid gives you

Like many of you I use AWR reports all the time to see what is happening in the database, and especially to compare between different points in time.. Whenever the users tell me the system is "running slow", I always try to find a comparison time.. "what other day recently has a similar workload as today", and run an AWR Comparison between the time periods. Through Grid (or dbconsole), this can be frustrating for a RAC database. Sometimes you want to compare between nodes for the same period, or different periods across nodes. This is only the beginning.. I also want to compare across databases.

As you can guess the reports available through the grid don't give you these choices. But guess what ? DBReplay gives you these choices. In order to support DBReplay, Oracle has added some pretty nifty features into AWR.

First a non-dbreplay feature, the "colored SQL".

As many of you know, Oracle only saves the top 50 SQL of interest. Of course you can change the number of top sql saved with the MODIFY_SNAPSHOT_SETINGS procedure.

dbms_workload_repository.modify_snapshot_settings(
retention IN NUMBER DEFAULT NULL,
interval IN NUMBER DEFAULT NULL,
topnsql IN NUMBER DEFAULT NULL,
dbid IN NUMBER DEFAULT );


The problem is, what happens if you are interested in a SQL that isn't in the top sql statements ? If you have a very active system, you might find that the sql isn't in the top 50, or even the 100. So what is there to do ? "color the sql". Use this procedure to mark sql to gather information about the SQL_ID every snapshot even if it isn't a top sql. Here is the description

Routine to add a colored SQL ID. If an SQL ID is colored, it will always be captured in every snapshot, independent of its level of activities (i.e. does not have to be a TOP SQL). Capturing will occur if the SQL is found in the cursor cache at snapshot time

dbms_workload_repository.add_colored_sql(
sql_id IN VARCHAR2,
dbid IN NUMBER DEFAULT NULL);

Now onto my original problem.

How do I do comparisons against instances or even database ? Well when I took a good look at the AWR_DIFF_REPORT_HTML procedure, I noticed that you can call it with multiple parameters (like instance ID and dbid).

dbms_workload_repository.awr_diff_report_html(
dbid1 IN NUMBER,
inst_num1 IN NUMBER,
bid1 IN NUMBER,
eid1 IN NUMBER,
dbid2 IN NUMBER,
inst_num2 IN NUMBER,
bid2 IN NUMBER,
eid2 IN NUMBER)
RETURN awrrpt_html_type_table PIPELINE;

If you run awr_diff_report with the 2 different instances you compare them against each other. Now how do you do database ? Look at metallink note 872733.1 (yes I still call it metalink). This note tells you how to export the AWR information into a file, and import it into a new database.

Here is my plan to handle all this.

1) Create a centralized repository of all AWR information for all database in the infrastructure..

2) Follow the metalink note to export/import data into the centeralized repository

3) In the centralized repository create a table mapping DBID to source database.

4) Configure APEX (application Express), to pick DBID's, Instances, and snapshot ranges to run a comparison report. Display the report in APEX as a webpage.

This is my summer project, and I will let everyone know how it goes.

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