Preventing runaway queries

Joe, a business analyst often runs big reports in the middle of the day that take up the whole machine's resources.You want to prevent Joe from using more than 100MB of memory, and you want to also limit Joe's queries to run for less than 2 hours.

Scenario

Joe, a business analyst often runs big reports in the middle of the day that take up the whole machine's resources.You want to prevent Joe from using more than 100MB of memory, and you want to also limit Joe's queries to run for less than 2 hours.

Solution

User profiles provides a solution to this scenario. To restrict the amount of memory Joe can use at one time, set a MEMORYCAP for Joe to 100MB using the ALTER USER command. To limit the amount of time that Joe's query can run, set a RUNTIMECAP to 2 hours using the same command. If any query run by Joe takes up more than its cap, Vertica rejects the query.

If you have a whole class of users whose queries you need to limit, you can also create a resource pool for them and set RUNTIMECAP for the resource pool. When you move these users to the resource pool, Vertica limits all queries for these users to the RUNTIMECAP you specified for the resource pool.

Example

=> ALTER USER analyst_user MEMORYCAP '100M' RUNTIMECAP '2 hours';

If Joe attempts to run a query that exceeds 100MB, the system returns an error that the request exceeds the memory session limit, such as the following example:

\i vmart_query_04.sqlvsql:vmart_query_04.sql:12: ERROR:  Insufficient resources to initiate plan
on pool general [Request exceeds memory session limit: 137669KB > 102400KB]

Only the system database administrator (dbadmin) can increase only the MEMORYCAP setting. Users cannot increase their own MEMORYCAP settings and will see an error like the following if they attempt to edit their MEMORYCAP or RUNTIMECAP settings:

ALTER USER analyst_user MEMORYCAP '135M';
ROLLBACK:  permission denied