We have come a long way from Oracles old statspack reports.
Remember way back. Ok, maybe not too way back, when we
would run the old statspack reports. A DBA would run begin-stats, wait a while,
and then run end-stats. At the end of the end-stats routine a report would kick
out that would show you all the accumulated statistics for the time period
between begin-stats and end-stats. I know a lot of DBAs that just loved this.
The information was fine but what happened to the statistics after the report
was generated? The data was gone since the beginning of the begin-stats would
truncate or delete all the tables that held the statistical data from the last
time the procedures where executed. The data was very short lived.
Enter in the age of snapshots and what Oracle has called the
Automatic Workload Repository (AWR). Now a DBA can schedule a collection
procedure (snapshot) to instruct Oracle to take the end-stats. These statistics
are now stored in the database along with a predefined number of other
snapshots. DBAs can now just give AWR more space and increase the retention for
data and now statistics can be held around for as long as desired. This is a
GREAT improvement and I hope you can see the benefit. Now, for a database, DBAs
can go back in time and see exactly how a database was performing at a
particular point-in-time. In addition, DBAs can compare two different
points-in-time to see what might have changed or if tuning attempts actually
produced performance benefits. Very powerful!
The next logical step is to want to compare point-in-time
snapshots from two different databases. Up until now, this was impossible and
reports could only be run against a single database. This is where Oracles
Transportable Automatic Workload Repository comes in. Now a DBA can take a set
of statistics from one database and transport them into another. This could be
into a database that is currently doing some task (production/test/QA/stress)
or as I would suggest into an actual repository whose sole purpose is to house
AWR data. You decide, but by creating just a repository for extracted AWR data,
you in essence are able to perform detailed analysis without impacting your
Oracle Data Pump & DIRECTORY Objects
Before we get into the example, be aware that the utilities
provided by Oracle to transport AWR data use Data Pump and DIRECTORY objects.
By default, after installation, Oracle has a DATA_PUMP_DIR already created that
can be used for the procedures. This can be seen by the following query.
SQL> select * from DBA_DIRECTORIES
where directory_name = 'DATA_PUMP_DIR';
OWNER DIRECTORY_NAME DIRECTORY_PATH
----- --------------- ------------------------------------------------------
SYS DATA_PUMP_DIR /opt/app/oracle/product/10.2.0/db_1/
For those that are security conscious and might have dropped
this object, one can be created by the following.
SQL> CREATE DIRECTORY DATA_PUMP_DIR
You can actually name your DIRECTORY object anything you
wish and use any directory. The prior examples are just a starting point. Just
keep in mind that you will need to grant the following authorizations to who
ever uses Data Pump. Not a big issue as the transportable routines are supposed
to be run as the sys user but thought I would mention them here.
SQL > GRANT EXP_FULL_DATABASE to <user>;
SQL > GRANT READ, WRITE ON DIRECTORY datapump to <user>;
How to Extract AWR Data
Oracle provides a script called awrextr.sql that will
prompt for the various pieces of information that distinguish a unique snapshot
from the database. This script needs to run as the sys user and on a
machine that has access to the $ORACLE_HOME/rdbms/admin directory. Simply log
into the database as the sys user and invoke the script. The output from
the beginning of the awrextr.sql script says it all on what will be
expected to complete the script successfully.
~ This script will extract the AWR data for a range of snapshots ~
~ into a dump file. The script will prompt users for the ~
~ following information: ~
~ (1) database id ~
~ (2) snapshot range to extract ~
~ (3) name of directory object ~
~ (4) name of dump file ~
During the run of the awrextr.sql script, Oracle
intellectually displays vital information that you might want to use for the four
different prompts above. However, after entering this information into Oracle, the
extract routine takes on the look of a typical Data Pump run where it shows you
the objects being extracted along with row counts. Depending on the number of
snapshots you plan to extract, this script could run for a bit. If you plan to
transport data between systems, I would suggest you do it in reasonable chunks.
How to Load AWR Data
Loading the extracted AWR data is just as easy as the
extraction. Oracle provides a script called awrload.sql that will also
prompt for some basic information. This script, though, does not load directly
into the sys schema. It will load, via Data Pump, into a staging schema.
At first I thought this was a bit silly but have grown to appreciate the fact
that things can and will go wrong. If something does, you will be glad you used
a staging area, as the cleanup of AWR snapshot data is sometimes tricky. In
addition, if your two databases dont share the same DATA_PUMP_DIR you will
have to copy the previously extracted file to the DATA_PUMP_DIR of the target
database. Again, simply log into the target database for loading your AWR
stats as the sys user and invoke the script. The output from the
beginning of the awrload.sql script says it all on what will be expected
to complete the script successfully.
~ This script will load the AWR data from a dump file. The ~
~ script will prompt users for the following information: ~
~ (1) name of directory object ~
~ (2) name of dump file ~
~ (3) staging schema name to load AWR data into ~
The item that is not mentioned here is the fact you will be
creating a new user for the staging schema. As such, you will be prompted for a
DEAFULT TABLESPACE and a TEMPORARY TABLESPACE for this staging user. As a
precautionary measure, you might want to check that the user you use for the
staging schema is not already being used. There is a drop at the end of this
script and I would hate for the script to not only load bogus information into
that schema but also possibly drop the whole schema at the end.
Note: Dont use .dmp on the end of your files when
prompted for them
scripts awrextr.sql & awrload.sql prompt for file name to be
used for Data Pump. Just remember to not qualify by putting the suffix .dmp or
else the scripts will not find them.
What to DO NOW!
Most everyone is familiar with running AWR reports on a
single instance. NOW we have multiple instances in a shared AWR repository.
Yes, you can easily run the same single instance reports you have grown to love
but it is much more interesting to compare various instances that might be used
for the same purpose. Suppose you are in a development shop where you
continually run an application through QA. Often times you need to tune the
database and rerun a QA test. After doing this and loading the AWR data into a
repository you can now compare the two runs to see if there were any benefits to
performance. The script you want to use for this is called awrddrpi.sql. It
will prompt you to specify two database instances, or they could be the same,
and then prompt you for the snapshot time periods to be compared. I have
provided two snippets for your enjoyment to see the power of comparing
different AWR information.
Where to go from here
Since all of these utilities have been initiated from
scripts in the $ORACLE_HOME/rdbms/admin directory I always like to go and read
those scripts to really figure out what they are doing. More often than not,
there are jewels to be had where you investigate how to call and perform the
same functionality through your own scripts or create PL/SQL procedures that
will do this for you. The fact that these scripts extract and load through Data
Pump mean there is no reason you couldnt internalize the same routines in a set of
PL/SQL packages that are tailored for your own environment. Here are a couple
of the packages/procedures called. I am sure you can now determine what they
Honestly, I think the introduction of Oracle RAC really had
to make Oracle think about how their previous utilities had been written. No
longer do we as DBAs want only to interact with a single database instance. We
want to compare, contrast, and do general investigative analysis across
databases. I am personally glad RAC is around if nothing more than to get some
more power into these utilities.
Note: Oracle Database 10g Licensing Information
AWR is part
of the Database Diagnostics Pack and by definition is a premium feature where
an additional license must be purchased before being used.
See All Articles by Columnist James Koopmann