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Monitoring and Testing I/O

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1 Monitoring and Testing I/O
Using Perfmon, Oracle tools and IOMeter for monitoring and load testing the I/O Subsystem

2 Objectives At the end of this module the student will understand the following tasks and concepts. Monitoring the I/O Subsystem using Perfmon Monitoring the I/O Subsystem using Oracle Tools Load Testing the I/O Subsystem using TTCP

3 Oracle and I/O I/O performance is crucial to Oracle Performance
Data buffers are sensitive to read I/O latency Log buffers are sensitive to write I/O latency Any slowdown in I/O performance can cause a significant performance loss for Oracle. Although Oracle uses Buffer Cache very effectively, all data must at some point be read into memory, andall transactions must be written out to the redo log files..

4 Oracle I/O Problems Performance Degradation
Index lookup 10 I/Os 10 x 6 ms = 60 ms (not bad) 10 x 100 ms = 1 sec (noticeable) Table Scan 30,000 I/Os 30,000 x 6 ms = 90 sec (not bad for a Table Scan) 30,000 x 100 ms = 3,000 sec = 50 minutes You are getting phone calls and s

5 Monitoring I/O Performance Perfmon
General Tips Set the sample rate up 1 sec is too fast Not accurate on all counters Not enough time to see all the counters Way to fast for saving the data Heizenburg Uncertainty Principle Use both graph and report as appropriate Save data if possible

6 Monitoring I/O Performance Perfmon
Logical Disk Counters Lists the Physical Disks by Drive Letter Good for monitoring file I/O Physical Disk Counters Lists the Physical Disks by Physical Disk Good for monitoring the LUNs or Volumes

7 Monitoring I/O Performance Perfmon
Latencies IOPS (I/Os Per Second) Throughput I/O sizes

8 Monitoring I/O Performance Perfmon
Latencies Avg. Disk sec/Read Provides Read Latency Statistics Avg. Disk sec/Write Provides Write Latency Statistics

9 Monitoring I/O Performance Latency

10 Monitoring I/O Performance Perfmon
IOPS Disk Reads/sec Disk Transfers/sec Useful for total volume IOPS (remember RAID overhead) Disk Writes/sec

11 Monitoring I/O Performance IOPS

12 Monitoring I/O Performance Perfmon
Throughput Disk Bytes/sec Total Throughput Disk Read Bytes/sec Disk Write Bytes/sec

13 Monitoring I/O Performance Throughput

14 Monitoring I/O Performance Perfmon
I/O sizes Avg. Disk Bytes/Read Avg. Disk Bytes/Write These counters provide information that allows you to get a little bit of an idea of what Oracle is doing. When Oracle is doing index lookups or random reads and writes the standard block size of 8 KB will be used and you will see an 8 KB Avg. Disk Bytes/Read and an 8 KB Avg. Disk Bytes/Write. When Oracle is doing table scans the block size will be much larger. The maximum size is determined by the maximum I/O size allowable by the OS. In addition, the Oracle log writes are variable based on how much data is in the log buffer when the log writer thread is ready to write it out.

15 Monitoring I/O Performance I/O Sizes

16 Monitoring I/O Performance Perfmon
Miscellaneous Current Disk Queue Length The current disk queue length could give you an indication that there are performance problems with the I/O subsystem. With SAN storage the disk queue length should not be over 1 or 2. If this number is very high you should investigate further. This is not as good of an indication of a slowdown as the latency counters.

17 Monitoring I/O Performance Oracle Tools
OEM Performance Page Instance Disk I/O Instance Throughput

18 Monitoring I/O Performance Oracle Tools
Oracle Counters for Windows Performance Monitor Add Oracle Data Files counter physreads/sec Physwrites/se Choose data files to monitor Shows I/O for database files

19 Monitoring I/O Performance Oracle Tools
STATSPACK Reports Tablespace IO Stats Data File IO Stats Tablespace IO Stats for DB: DSSA Instance: dssa4 Snaps: 1 -2 ->ordered by IOs (Reads + Writes) desc Tablespace Av Av Av Av Buffer Av Buf Reads Reads/s Rd(ms) Blks/Rd Writes Writes/s Waits Wt(ms) UNDOTBS4 , USERS , TEMP TOOLS , SYSTEM File IO Stats for DB: DSSA Instance: dssa4 Snaps: 1 -2 ->ordered by Tablespace, File Tablespace Filename SYSTEM /u11/dssa/system01.dbf TEMP /u11/dssa/temp01.dbf TOOLS /u11/dssa/tools01.dbf , UNDOTBS /u11/dssa/undotbs04.dbf , USERS /u11/dssa/users01.dbf ,

20 Load Testing I/O Used to determine I/O problems in a controlled and scientific manner Used to identify the upper limits of the storage subsystem Used to prove or disprove hypothesis or theories

21 Load Testing I/O IOMeter
IOMeter is a public domain utility Available at Generates I/O based on your specifications Provides accurate results Is repeatable

22 Load Testing I/O IOMeter
Made up of two major components GUI Used for configuration and results Dynamo Used to generate the load

23 Load Testing I/O IOMeter
Configuring IOMeter Disk Targets Network Targets Access Specifications Results Display Test Setup

24 Load Testing I/O Disk Targets
Maximum Disk Size For random I/Os this must be sufficiently large # of Outstanding I/Os Defines concurrency of I/Os If set to one there will only be one I/O issued at a time and IOPS = 1 / latency The maximum disk size should be sufficiently large to cause seeking on the disk drives. In some cases, this must be very large. A maximum disk size that is too small will skew your results. The number of outstanding I/Os must be sufficiently high to simulate Oracle asynchronous I/O. If you leave it at the default of 1, only one I/O will be outstanding at time, thus resulting in no queueing.

25 Load Testing I/O Network Targets
Used for network I/O testing

26 Load Testing I/O Access Specifications
Specifies the type of I/O Block Size Read/Write ratio Sequential/Random Ratio Create new spec for Oracle

27 Load Testing I/O Test Setup
Used to set up automated tests Run time Ramp up Number of workers Etc.

28 Load Testing I/O Results Display
View the performance during the test IOPS Throughput Latency CPU Utilization

29 Review What type of I/O problem causes the biggest problem with Oracle Data Files ? Name some Perfmon counters to monitor for I/O? What counter does the Oracle Counters for Windows Performance Monitor add to Perfmon that measures Oracle I/O? What are the two components of IOMeter?

30 Summary Monitoring the I/O Subsystem using Perfmon
Monitoring the I/O Subsystem using Oracle Tools Load Testing the I/O Subsystem using TTCP

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