dmann's blog

Oracle IN Condition and Multi Column Subqueries

I keep coming across a construct in some legacy SQL that has been causing all kinds of performance issues for us. I guess you could call it using the IN condition with multi-column subqueries. I located the syntax for the IN condition here but it doesn't really get into much detail about using this construct. Here is an example of the subquery (it returns the lowest salary and department_id for each department):

SQL For Dinosaurs


Quickie script to run dbv on your database...

This script will generate dbv commands into a shell script and then execute the shell script. run-dbv.sql:
set head off
set lines 200
set feedback off
set define off

select 'dbv file='||name||' blocksize = '||block_size||
       ' LOGFILE=FILE-'||FILE#||'.LOG' from v$datafile;
spool off

host chmod 755
spool dbv_results.log
host ./
spool off
Output will be created as separate log files. You can run it and review results like this:
$ sqlplus "/ as sysdba" @run-dbv.sql

Permissions for Autotrace

If you want to run AutoTrace using Toad using a non sys or system user, give your user the following select privileges:
grant select on v_$session to &traceuser.;
grant select on v_$sesstat to &traceuser.;
grant select on v_$statname to &traceuser.;
Alternately you can run $ORACLE_HOME/sqlplus/admin/plustrce.sql and then grant the PLUSTRACE role to the user that needs to run AutoTrace. -Dave

Accuracy of PROFILER.SQL from Metalink Doc: 243755.1

I came across a situation where the profiler.sql supplied with Metalink Doc: 243755.1 was giving some incomplete results. Because some of my PL/SQL code was executing very quickly it was rounding down to 0.00 and not even showing up on the 'Top 10' section.

Throughout profiler.sql there are timing numbers (unit = sends) that are rounded to 2 places. Looking in the comments for profiler.sql I noticed the last update was early 2007. Maybe Moore's law and CPU power has caught up with profiler.sql but I would recommend increasing the granularity of the script by doing the following:

Recording Oracle System Stats for historical analysis...

If you are experimenting with gathering system statistics it might be helpful to archive your current settings and any intermediate settings you come up with along the way.

There is a way to save stats to a table using DBMS_STATS.CREATE_STAT_TABLE and gathering with DBMS_STATS.GATHER into that table, but the format is cryptic and it is nice to have the descriptive parameter names tagging along with the data. (In a future post I will cover format of the CREATE_STAT_TABLE format).

The current system stats info is held in the sys.aux_stats$ table. Since the format is a little wacky, I came up with the following table to hold stats and the following insert statement to populate it after every gathering of system stats.

Now you can easily query the values of old stats in the SYSTEM_STATS_HISTORY table:

Shell Script to Run a SQLPLUS against all databases running on a server...

# Written by  : David Mann @
# Script Name :
# Description : Provides list of all datafiles for each running database on 
#               on a machine


# Step through running instances
ps -ef | grep ora_smon_ | grep -v grep | cut -b61-70 | while read LINE
    # Assign the ORACLE_SID

Viewing command line args with Solaris ps utility...

If you ever used the Solaris ps -ef command to view programs that are running you may not always see the arguments the original program was started with. This command usually shows about 80 characters. Try the following commands, they usually give you more information about the command that started the process running. Depending on the patch level of your OS you may see 200 characters or more.
/usr/ucb/ps -auxwww

Orion IO Test Tool

I ran across Orion in a Kevin Closson blog post. From the OTN site:

"ORION (Oracle I/O Calibration Tool) is a standalone tool for calibrating the I/O performance for storage systems that are intended to be used for Oracle databases. The calibration results are useful for understanding the performance capabilities of a storage system, either to uncover issues that would impact the performance of an Oracle database or to size a new database installation. Since ORION is a standalone tool, the user is not required to create and run an Oracle database. "

Documented Hints available in 11.2...

As I get deeper into tuning with Statistics and the CBO I have been paying a lot more attention to hints. In the past I always tried to avoid hints. After working with the CBO and staistics in recent versions I believe they are necessary at times to give guidance to the CBO. The Oracle Database SQL Language Reference has a comprehensive list of hints included in the documentation of SQL Comments. The list for 11g is available here: link.


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