Finding Query Block names for a SQL that you can't modify...

I recently had an issue where a query being submitted to the database had a large change in performance. I could attribute the change to a recent change in object statistics, but the query wasn't behaving because of a combination of a view, subquery, UNION, and LIKE operators. After spending too much time on this statement I decided to hint it to make it perform like it did before the most recent stats change.

Need to audit changes? Can't change source database at all? This may work...

If you want to record copies of changed records on a target system you can do this with Golden Gate Software and not incur much in the way of source side resource drain.

Unloading data from Oracle?

I recently fielded a question about getting data out of Oracle quickly. Without much detail on the systems involved here is my answer:

Question:

I need to migrate data from Oracle to MySQL quickly (in less than 1 day). What are my options?

My answer:

Oracle does not supply an out-of-the-box unload utility. Keep in mind without comprehensive info about your environment (oracle version? server platform? how much data? what datatypes?) everything here is YMMV and you would want to give it a go on your system for performance and timing.

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):
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SQL For Dinosaurs

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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
spool dbv.sh

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

host chmod 755 dbv.sh
spool dbv_results.log
host ./dbv.sh
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...

#!/usr/bin/bash
#---------------------------------------------------------------------------
# Written by  : David Mann @ http://ba6.us
# Script Name : alldatafiles.sh
# Description : Provides list of all datafiles for each running database on 
#               on a machine
#---------------------------------------------------------------------------

ORATAB=/etc/oratab
echo "INSTANCE_NAME, FILE_NAME"

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

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