ba6.us - Dave's Database Related Stuff

...well not yet...

An Infoworld article was released today describing an Oracle vulnerability. The SCN space can be exhausted via bugs or attackers exploiting bugs. Metalink doc: 1376995.1 [Bulletin : Information on the System Change Number (SCN) and how it is used in the Oracle Database] covers a technical description for what SCNs are used for.

You can use this query to find out how close you are to the SCN limit. Read more »

I started a new project for a utility I started writing. It has some basic functionality now but will probably increase in utility int he future.

It is a Perl script that extracts the SQL statements from an Oracle 10046 trace file. This is useful if you need to re-run SQL that was captured during a trace. It also helps reduce the amount of junk you have to slog through if you are interested in

trc2sql.pl - Extract SQL Statements From Oracle 10046 Trace File

-Dave

Oracle is supplying some ready-to-run downloadable VMs including Operating Systems, OSes with Oracle already installed and ready-to-run RAC systems. I was hoping to leverage these to save some time for sandbox environments but from what I have seen so far they are only for the enterprise level Oracle VM product. I only have the horsepower to run Oracle VirtualBox which is their workstation level product. It seems they use different formats for each product and while it may be possible to convert VMs backs and forth, I'm just not up for it right now.

Came upon this post during my travels. Jonathan Lewis reveals how to write a string to the Alert Log, Current Session Trace File, or Both. Also a few misc functions are included.

dbms_system.ksdwrt(1,'test')
    writes to alert log

dbms_system.ksdwrt(2,'test')
    writes to session's trace file

dbms_system.ksdwrt(3,'test')
    writes to both

see also 
    dbms_system.ksddt - writes a date-time stamp
    dbms_system.ksdind(N) - indents text using ":' characters
 Read more »

I shared a shell script that will check Oracle CDC Queues to make sure they aren't going stale. If your CDC consumer has not picked up changes in 48-72 hours then something may be wrong. The scripts can be customized to alert at any interval, hopefully this will serve as a good 'nudge' to get you going in the right direction.

Everything you need is here.

If you are an OEM user you can probably grab the SQL I shared and modify it for use with OEM User Defined Metrics or alerting.

-Dave

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.

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):

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
 Read more »

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:

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. " Read more »