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The described scenario, a crash due to storage used up by a TABLE as
output from a cross join, is best prevented by one or more of:
- MAXSTG() parameter for the user that owns the output file.
- SIZE() parameter on the output file.
- Break handling program on QSYSMSG *MSGQ which will see the storage
messages
- System value QSTGLOWACN set to *REGFAC, then QIBM_QWC_QSTGLOWACN
exit point with format STGL0100, according to sysval QSTGLOWLMT see:
http://publib.boulder.ibm.com/infocenter/iseries/v5r4/topic/rzakz/rzakzqstglowacn.htm
Note: in the above system value, perhaps using the *CRITMSG settings
defined by CHGSRVA to identify those to be notified via message CPI099B,
to defer action to an operator.
And for temporary storage being an issue instead, one or more of:
- temporary storage limit for a job via the class [CHGCLS]
- tmpstg limit via the query attributes [CHGQRYA QRYSTGLMT()]
The origin of the issue is the TABLE which enables no limits
protection, and thus is outside of the query itself. AFaIK there is no
control at the SQL statement level nor session level for such an issue,
except to use the FETCH FIRST x ROWS ONLY clause. That could be used by
a utility, such as QM /temporary/ cached results or DB2 Web Query, to
implement a protection, but the SQL engine itself can not implicitly
limit a statement [for those who would ask why it does not; e.g. just to
be sure to /prevent/ a crash].
Regards, Chuck
Lukas Beeler wrote:
On Tue, Aug 12, 2008 at 6:51 PM, <elehti@xxxxxxxxxxxxxxxxxx> wrote:
How to fill up your disk (system auxiliary storage pool) and take
down your system. Create a query to output to a file. Join two or
more tables but neglect to join the tables. This will produce a
Cartesian join. http://www.orafaq.com/wiki/Cartesian_join
I don't have much to do with the DBA side of things on the i, but I'm
sure you can limit the resources that are allowed to be used by a
single query, or the storage used by a single user/login.
I know that i can do this kind of stuff in SQL Server.
midrange.com
