Martins Blog

Trying to explain complex things in simple terms

Viewing Runtime Load Balancing Events

Posted by Martin Bach on January 20, 2011

Yesterday I have run a benchmark on a 2 node RAC cluster (ProLiant BL685c G6 with 4 Six-Core AMD Opteron 8431) and 32G RAM each. It’s running Oracle Grid Infrastructure 11.2.0.2 as well as an Oracle 11.2.0.2 database on Oracle Enterprise Linux 5.5 64bit and device-mapper-multipath.

I was testing how the system would react under load but also wanted to see if the Runtime Load Balancing was working. The easiest way to check this is to view the AQ events that are generated for a service if AQ HA notifications is set to true. They can either be dequeued from the database as described in chapter 11 of Pro Oracle Database 11g RAC on Linux or alternatively queried from the database. The latter is the quicker method and this article will focus on it.

Before you can make use of Runtime Load Balancing you need to set at least 2 properties in your service:

  • Connection Load Balancing Goal (either SHORT or LONG)
  • Runtime Load Balancing Goal (SERVICE_TIME or THROUGHPUT)

.Net applications require AQ HA notifications to be set to true as these can’t directly make use of Fast Application Notification (FAN) events as said in the introduction. My JDBC application is fully capable of using the FAN events, however as you will see later I am using the AQ notifications anyway to view the events.

Connected as the owner of the Oracle binaries, I created a new service to make use of both instances:

$ srvctl add service -d TEST -s TESTSRV -r TEST1,TEST2 -P BASIC  \
> -l PRIMARY -y MANUAL -q true -x false -j short -B SERVICE_TIME \
> -e SESSION -m BASIC -z 0 -w 0

The service TESTSRV for database TEST has TEST1 and TEST2 as preferred instances, and the service should be started (manually) when the database is in the primary role. AQ Notifications are enabled, and I chose the connection load balancing goal to be “short” (usually ok with web applications and connection pooling) and a runtime load balancing goal of service time (should also be appropriate for many short transactions typical for a web environment). The remaining paramters define Transparent Application Failover. Please refer to the output of “srvctl add service -h” for more information about the command line parameters.

The result of this endavour can be viewed with srvctl config service:

$ srvctl config service -d TEST -s TESTSRV
Service name: TESTSRV
Service is enabled
Server pool: TEST_TESTSRV
Cardinality: 2
Disconnect: false
Service role: PRIMARY
Management policy: MANUAL
DTP transaction: false
AQ HA notifications: true
Failover type: SESSION
Failover method: BASIC
TAF failover retries: 0
TAF failover delay: 0
Connection Load Balancing Goal: SHORT
Runtime Load Balancing Goal: SERVICE_TIME
TAF policy specification: BASIC
Edition:
Preferred instances: TEST1,TEST2
Available instances:

So to begin with I created the order entry schema (SOE) in preparation of a swingbench run. (I know that Swingbench’s Order Entry is probably not the best benchmark out there but my client knows and likes it). Once about 10G of data were generated I started a swingbench run with 300 users, and reasonably low think time (min transaction time 20ms and max of 60ms). The connect string was //scan1.example.com:1800/TESTSRV

A query against gv$session showed an even balance of sessions, which was good:

select count(inst_id), inst_id
 from gv$session
where username = 'SOE'
group by inst_id

However, whatever I did I couldn’t get the Runtime Load Balancing in sys.sys$service_metrics_tab to chanage. They always looked like this (column user_data):

{instance=TEST1 percent=50 flag=UNKNOWN aff=TRUE}{instance=TEST2 percent=50 flag=UNKNOWN aff=TRUE} }

That sort of made sense as none of the nodes broke into a sweat-the system was > 50% idle with a load average of about 12. So that wouldn’t cut it. Instead of trying to experiment with the Swingbench parameters, I decided to revert back to the silly CPU burner: a while loop which generates random numbers. I wasn’t interested in I/O at this stage, and created this minimal script:

$ cat dothis.sql
declare
 n number;
begin
 while (true) loop
 n:= dbms_random.random();
 end loop;
end;
/

A simple for loop can be used to start the load test:

$ for i in $(seq 30); do
> sqlplus soe/soe@scan1.example.com:1800/TESTSRV @dothis &
done

This created an even load on both nodes. I then started another 20 sessions on node1 against TEST1 to trigger the change in behaviour. And fair enough, the top few lines of “top” revealed the difference. The output for node 1 was as follows:


top - 10:59:30 up 1 day, 21:16,  6 users,  load average: 42.44, 20.23, 10.07
Tasks: 593 total,  48 running, 545 sleeping,   0 stopped,   0 zombie
Cpu(s): 99.9%us,  0.1%sy,  0.0%ni,  0.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:  32960688k total, 11978912k used, 20981776k free,   441260k buffers
Swap: 16777208k total,        0k used, 16777208k free,  8078336k cached

Whereas node 2 was relatively idle.

top - 10:59:22 up 5 days, 17:45,  4 users,  load average: 15.80, 10.53, 5.74
Tasks: 631 total,  16 running, 605 sleeping,  10 stopped,   0 zombie
Cpu(s): 58.8%us,  0.6%sy,  0.0%ni, 40.6%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:  32960688k total, 11770080k used, 21190608k free,   376672k buffers
Swap: 16777208k total,        0k used, 16777208k free,  7599496k cached

Would that imbalance finally make a difference? It did, as the user_data column (truncated here for better readability) reveals:

</pre>
SQL> select user_data
 2  from sys.sys$service_metrics_tab
 3  order by enq_time desc;

{instance=TEST1 percent=4 flag=GOOD aff=TRUE}{instance=TEST2 percent=96 flag=GOOD aff=TRUE} } timestamp=2011-01-20 11:01:16')
 {instance=TEST1 percent=6 flag=GOOD aff=TRUE}{instance=TEST2 percent=94 flag=GOOD aff=TRUE} } timestamp=2011-01-20 11:00:46')
 {instance=TEST1 percent=10 flag=GOOD aff=TRUE}{instance=TEST2 percent=90 flag=GOOD aff=TRUE} } timestamp=2011-01-20 11:00:16')
 {instance=TEST1 percent=18 flag=GOOD aff=TRUE}{instance=TEST2 percent=82 flag=GOOD aff=TRUE} } timestamp=2011-01-20 10:59:46')
 {instance=TEST1 percent=28 flag=GOOD aff=TRUE}{instance=TEST2 percent=72 flag=GOOD aff=TRUE} } timestamp=2011-01-20 10:59:16')
 {instance=TEST1 percent=35 flag=GOOD aff=TRUE}{instance=TEST2 percent=65 flag=GOOD aff=TRUE} } timestamp=2011-01-20 10:58:46')
 {instance=TEST1 percent=40 flag=GOOD aff=TRUE}{instance=TEST2 percent=60 flag=GOOD aff=TRUE} } timestamp=2011-01-20 10:58:16')
 {instance=TEST1 percent=43 flag=GOOD aff=TRUE}{instance=TEST2 percent=57 flag=GOOD aff=TRUE} } timestamp=2011-01-20 10:57:46')
 {instance=TEST1 percent=44 flag=GOOD aff=TRUE}{instance=TEST2 percent=56 flag=GOOD aff=TRUE} } timestamp=2011-01-20 10:57:16')
 {instance=TEST1 percent=48 flag=GOOD aff=TRUE}{instance=TEST2 percent=52 flag=GOOD aff=TRUE} } timestamp=2011-01-20 10:56:46')
 {instance=TEST1 percent=49 flag=GOOD aff=TRUE}{instance=TEST2 percent=51 flag=GOOD aff=TRUE} } timestamp=2011-01-20 10:56:16')
 {instance=TEST1 percent=50 flag=GOOD aff=TRUE}{instance=TEST2 percent=50 flag=GOOD aff=TRUE} } timestamp=2011-01-20 10:55:46')
 {instance=TEST1 percent=50 flag=GOOD aff=TRUE}{instance=TEST2 percent=50 flag=GOOD aff=TRUE} } timestamp=2011-01-20 10:55:16')
 {instance=TEST1 percent=50 flag=UNKNOWN aff=TRUE}{instance=TEST2 percent=50 flag=UNKNOWN aff=TRUE} } timestamp=2011-01-20 10:54:46')
 {instance=TEST1 percent=50 flag=UNKNOWN aff=TRUE}{instance=TEST2 percent=50 flag=UNKNOWN aff=TRUE} } timestamp=2011-01-20 10:54:16')

Where it was initially even at 50-50 it soon became imbalanced, and TEST2 would be preferred after a few minutes in the test.  So everything was working as expected, I just didn’t manage to put enough load on the system intially.

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