Performance Scenario:
Diagnosing and resolving sudden
slow down on two node RAC

Introduction…
• Karl Arao, OCP‐DBA, RHCT
• Senior Consultant at SQL*Wizard
• RAC user for 3years
• 1st environment on VMware
• I “heart” performance
• Don’t like to guess when troubleshooting

Scenario
One Thursday…
a client called…
There was a SUDDEN
slow down
on ALL of the applications
…a big impact to the Business

And it’s running on
RAC RAC
no changes on the
RAC nodes and on the applications

Some of 10g Performance Features
• OEM Performance Page
• ADDM
• SQL Tuning advisor
• AWR (DBA_HIST_)
• ASH
• Time Model (total time for all db calls)
• Wait Class (12 wait class)
• Metrics (v$ performance metric deltas)
• Services

Setup
• Server and Storage: SunFire X4200 (2CPU,
12GB memory) with LUNs on EMC CX300
• OS: RHEL 4.3 ES
• Database and clusterware: Oracle 10.2.0.3
• Database Files, Flash Recovery Area, OCR, and
Voting disk are located on OCFS2 filesystems
• Application: Forms and Reports (6i and also
lower)

Troubleshooting Principle
Systematic/Layered approach..
Understand..
Then Fix..
Lets get it on!

1. Measured the OS stack
• Monitored the following
– cpu (vmstat, top, mpstat)
– io (iostat)
– memory (vmstat, meminfo)
– network (netstat)
– process info (top, ps)

• CPU on server1
• CPU on server2

• Datafiles on server1
• Datafiles on server2

• OCR & voting disk on server1
• OCR & voting disk on server2

• Archivelogs on server1
• Archivelogs on server2

• Flash Recovery Area on server1
• Flash Recovery Area on server2

• Memory on server1
• Memory on server2

2. Checked the DB environment
• Compared my past & current RDA of the
database
• Query on some v$views.. a query on v$session
showed that server1 has more connections
(89% of the total users)

2. Checked the DB environment
This could be because of:
1) The clients having lower versions (< Sql*Plus 8.1
or OCI8, see Note 97926.1) that may not support
TAF (FAILOVER_MODE) and Load Balancing
(LOAD_BALANCE)
OR
2) They are using TNS entries explicitly connecting
to server1

2. Checked the DB environment
• Users don’t have FAILOVER capabilities

2. Checked the DB environment
• Checked the application module usage on server1

2. Checked the DB environment
• How bout I graph it in excel? Will the data be more
meaningful?
.. YES  most of the users uses the xxxlogin.fmx module

3. Checked instance‐wide
DB performance
• Graphed the ASH data..
.. suffering from “gc cr block lost” and “gc cr multi block request” from 7am to 4pm

3. Checked instance‐wide
DB performance
• Researched on Metalink for known issues..
Found Doc ID: 563566.1 gc lost blocks
diagnostics
• Was able to pinpoint the peak period from the
graph. Then, generated ADDM and AWR
report on that peak period..

3. Checked instance‐wide
DB performance
• ADDM
Elapsed Time: 60min
DB Time: 61.83min
AAS: 1.03
Max CPU: 2

3. Checked instance‐wide
DB performance
• Should I follow these recommendations right away?
Nope  collect more facts, numbers, figures

3. Checked instance‐wide
DB performance
• AWR

3. Checked instance‐wide
DB performance
• Do we have a workload distribution problem?
Nope  even with distributed users..
We still have performance problem..

4. Checked session‐level
DB performance
• The database has too many activity, where do
I start? Where to drill down?
• gv$session_longops & gv$session_wait output
too many users, and require repetitive
monitoring
• In the spirit of Method‐R…
"WORK FIRST TO REDUCE THE BIGGEST RESPONSE TIME COMPONENT OF A
BUSINESS' MOST IMPORTANT USER ACTION“
• Went to the Accounting Department, checked
on the desktop terminals

4. Checked session‐level
DB performance
• Users PC1069 (with SID 601) and PC918 (with
SID 483) are on total hang

4. Checked session‐level
DB performance
• Checked on the
– performance/wait counters
– the current SQLs

4. Checked session‐level
DB performance
• v$session_wait (SID 601)

4. Checked session‐level
DB performance
• v$sesstat (SID 601)

4. Checked session‐level
DB performance
• v$sql, v$sql_plan, v$sql_plan_statistics (SID 601)
• Running for 98 minutes
• Just 12.14 seconds on CPU

4. Checked session‐level
DB performance
• v$sesstat (SID 483)

4. Checked session‐level
DB performance
• v$sql, v$sql_plan, v$sql_plan_statistics (SID 483)
• Running for 3 hours
• Just 2.68 seconds on CPU

4. Checked session‐level
DB performance
• Another graph of ASH

5. Drilled down on the network
interconnect
• Generated a “cat & egrep” command to look
for problems in the interconnect from the OS
Watcher “netstat” output
(from Metalink Doc ID: 563566.1 gc lost blocks diagnostics)

5. Drilled down on the network
interconnect
$ cat server1_netstat.dat | egrep ‐i "udpInOverflows|packet receive
errors|fragments dropped|reassembles failed|fragments dropped after
timeout"
34096 fragments dropped after timeout
306030 packet reassembles failed
15 packet receive errors
34096 fragments dropped after timeout
306268 packet reassembles failed
15 packet receive errors
34096 fragments dropped after timeout
306574 packet reassembles failed
… output snipped …

5. Drilled down on the network
interconnect
• Restarted the switch
STILL THERE IS A PERFORMANCE PROBLEM

5. Drilled down on the network
interconnect
• Replaced the switch
THEY GOT FAST

5. Drilled down on the network
interconnect
karao@karl:~/Desktop$ cat karlarao.dat | egrep ‐i "udpInOverflows|packet receive
errors|fragments dropped|reassembles failed|fragments dropped after timeout"
0 packet receive errors
0 packet receive errors
0 packet receive errors
0 packet receive errors
0 packet receive errors
0 packet receive errors
0 packet receive errors
0 packet receive errors
0 packet receive errors
0 packet receive errors
0 packet receive errors

5. Drilled down on the network
interconnect
• Another graph of ASH (Stacked graph)

5. Drilled down on the network
interconnect
• Another graph of ASH (3d view)

Conclusion
You don’t have to guess..
Even if it’s a RAC environment..
It just takes facts, numbers, figures
to solve a performance problem 

References and Tools
• http://karlarao.wordpress.com
• http://blog.tanelpoder.com
– http://www.tanelpoder.com/files/TPT_public.zip
– http://www.tanelpoder.com/files/PerfSheet.zip
– Neil Gunther & Tanel Poder ‐ Multidimensional Visualization of Oracle
Performance using Barry007 http://arxiv.org/pdf/0809.2532
• http://ashmasters.com
• http://www.perfvision.com
• http://www.method‐r.com
• Metalink Doc ID 97926.1 Failover Issues and Limitations [Connect‐time
failover and TAF]
• Metalink Doc ID 563566.1 gc lost blocks diagnostics
• Metalink Doc ID 301137.1 OS Watcher User Guide

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Contact me through:
karao@sqlwizard.com
0919‐267‐3389
889‐6999