Run preliminary statement in Jmeter JDBC request

Question

I am creating a JDBC performance test using JMeter to evaluate the performance of a set of queries on a RedShift cluster.

On RedShift, ResultSet caching is enabled by default and it can be disabled on single sessions by using the statement

SET enable_result_cache_for_session=false;

As documented here.

I cannot find a way to run this statement in JMeter before running my queries. If I insert it before the actual JDBC Request, JMeter complains about expecting exactly one query.

If I create in my thread group a "Once Only Controller" which is executed before running the queries (which are in a random order controller in the same thread group), its execution doesn't seem to affect caching:

Query time varies from 30 seconds for the first run to 250ms for subsequent ones.

The same happens if I try to setup a JDBC PreProcessor for each single query.

Is there a way to run this preliminary query using jmeter? Alternatively, is there a way to globally disable caching on a Redshift cluster?

Answer 1

You can alter this parameter using Parameter groups:

https://docs.aws.amazon.com/redshift/latest/mgmt/working-with-parameter-groups.html

In JMeter <= 5.0 , it's not working as a new connection is extracted from pool on each query so the setting is not active.

I opened an enhancement request for this and we provided a fix that is now in JMeter nightly build and should be available in 5.1:

• https://bz.apache.org/bugzilla/show_bug.cgi?id=62832

Try nightly build here:

• https://jmeter.apache.org/nightly.html

EDIT 21 february 2019:

JMeter 5.1 has been released with the feature.

You configure it on JDBC Connection Configuration:

Answer 2

I faced the same problem. Here how you can configure running "cache off" query:

1. In a "test plan" window - check the "Run Thread Groups consecutively"
2. create 2 thread groups
3. in thread group 1 - add JDBC request "set enable_result_cache_for_session to off;" query type (IMPORTANT) - Update statement (others didn't work for me)
4. in thread group 2 - put all other JDBC requests

TestPlan settings: Cache off jdbc request:

Answer 3

You need to do this only once per cluster, not for each query so if you set enable_result_cache_for_session to false using i.e. Query Editor it should be applied until you set it back to true

If you have to do this with JMeter I can only think of connecting to RedShift instance over SSH

You can do this using JMeter SSH Command Sampler (you will need to install it using JMeter Plugins Manager) and set the parameter via relevant SSH command.