Kill Db2 select statement after the declared time - select

Question

In Db2 LUW 9.7, how to implement a query timeout?
When performing queries, is there is a 'timeout' parameter that I can declare/implement somehow that will make a given query abort after a certain time?
So far, I can only consider the potentially unsafe practice of killing the process that performs the select query in Unix.

Answer 1

This question is not about programming, it is about administration.
A query will never "kill itself". But there are tools available which (after suitable configuration) will limit the resources that a query can consume at run time, and will cause the query to return an error (if desired) if such resources are exceeded.
You should never kill a process that is owned by a Db2-instance, doing that carries risk that you trash your database.
To control the resources (time, memory, CPU, disk, etc...) that a query can use, it is possible on V9.7 to use Workload-Manager. This requires configuration and experience to properly use it.
IBM also offered a Query-Patroller tool before IBM introduced the Workload Manager (WLM). This was a different solution than WLM. I think Query Patroller was also available in V9.7. It has since been replaced by WLM.

Answer 2

In principle there are two ways to achieve what you need, depending on whether you have the control over the application or the database.
From application end one can use SQL_ATTR_QUERY_TIMEOUT keyword with CLI/ODBC or setQueryTimeout with JDBC (there should be an equivalent for other interfaces). I will attach CLI example at the end.
If you have only control over database then one could consider creating a threshold with ACTIVITYTOTALTIME that would automatically interrupt long running queries.
If you are concerned with Db2 CLP client, then interrupting execution with ctrl+c will propagate interrupt to the database, i.e. you should no longer see statement as executing inside the database. If you however break it more "forcefully" e.g. run kill against db2bp process associated with the shell, statement will continue executing for some time, but it will be eventually interrupted (one will see AgentBreathingPoint Warning in db2diag.log, when Db2 engine periodically checks whether client is still around and it happens to be gone).
Db2 CLI example:
I will use
db2cli executable - CLI to run Db2 CLI commands
"bad query" that is expected to run for a long time:
select t1.*, t2.* from sysibm.syscolumns t1, sysibm.syscolumns t2, sysibm.syscolumns t3, sysibm.syscolumns t4, sysibm.syscolumns t5 order by t5.name desc, t4.name asc fetch first 10 rows only
set the timeout to 10 seconds
code:
SQLAllocEnv 1
SQLAllocConnect 1 1
SQLConnect 1 SAMPLE sql_nts db2v115 sql_nts **** sql_nts
SQLAllocStmt 1 1
SQLSetStmtAttr 1 SQL_ATTR_QUERY_TIMEOUT 10
SQLPrepare 1 "select t1.*, t2.* from sysibm.syscolumns t1, sysibm.syscolumns t2, sysibm.syscolumns t3, sysibm.syscolumns t4, sysibm.syscolumns t5 order by t5.name desc, t4.name asc fetch first 10 rows only" sql_nts
SQLExecute 1
SQLFetch 1
SQLError 1 1 1
it is SQLFetch 1 that will fail, full output including SQLCODEs below:
$ db2cli
IBM DATABASE 2 Interactive CLI Sample Program
(C) COPYRIGHT International Business Machines Corp. 1993,1996
All Rights Reserved
Licensed Materials - Property of IBM
US Government Users Restricted Rights - Use, duplication or
disclosure restricted by GSA ADP Schedule Contract with IBM Corp.
> SQLAllocEnv 1
SQLAllocConnect 1 1
SQLConnect 1 SAMPLE sql_nts db2v115 sql_nts *** sql_nts
SQLAllocStmt 1 1
SQLSetStmtAttr 1 SQL_ATTR_QUERY_TIMEOUT 10
SQLAllocEnv: rc = 0 (SQL_SUCCESS)
CLI henv = 1, Test Driver henv = 1
> SQLAllocConnect: rc = 0 (SQL_SUCCESS)
CLI hdbc = 1, Test Driver hdbc = 1
> SQLConnect: rc = 0 (SQL_SUCCESS)
> SQLAllocStmt: rc = 0 (SQL_SUCCESS)
CLI hstmt = 1, Test Driver hstmt = 1
> SQLSetStmtAttr: rc = 0 (SQL_SUCCESS)
> SQLPrepare 1 "select t1.*, t2.* from sysibm.syscolumns t1, sysibm.syscolumns t2, sysibm.syscolumns t3, sysibm.syscolumns t4, sysibm.syscolumns t5 order by t5.name desc, t4.name asc fetch first 10 rows only" sql_nts
SQLPrepare: rc = 0 (SQL_SUCCESS)
> SQLExecute 1
SQLExecute: rc = 0 (SQL_SUCCESS)
> SQLFetch 1
SQLFetch: rc = -1 (SQL_ERROR)
> SQLError 1 1 1
SQLError: rc = 0 (SQL_SUCCESS)
SQLError: SQLState : S1008
fNativeError : -952
szErrorMsg : [IBM][CLI Driver][DB2/6000] SQL0952N Processing was cancelled due to an interrupt. SQLSTATE=57014
cbErrorMsg : 100

Answer 3

ODBC/CLI: QueryTimeout
JDBC: The commandTimeout property.
Common IBM Data Server Driver for JDBC and SQLJ properties for all supported database products
if I kill the process that performs the select query in Unix then the query should also be aborted
Yes.

Answer 4

create a threshold on ACTIVITYTOTALTIME or UOWTOTALTIME and set action on stop execution
https://www.ibm.com/support/knowledgecenter/en/SSEPGG_9.7.0/com.ibm.db2.luw.sql.ref.doc/doc/r0050563.html