Buffer Pool Cache Hit ratio is too low......

[ksc]

Hello.....

I'm workin on TSM6.1.3.3 Server and the output of "q db f=d" :

Database Name: TSMDB1
Total Size of File System (MB): 409,600
Space Used by Database(MB): 171,232
Free Space Available (MB): 237,754
Total Pages: 8,752,144
Usable Pages: 8,751,600
Used Pages: 8,742,820
Free Pages: 8,780
Buffer Pool Hit Ratio: 31.5
Total Buffer Requests: 96,343,498
Sort Overflows: 0
Lock Escalation: 0
Package Cache Hit Ratio: 99.3
Last Database Reorganization: 12/19/11 13:59:21
Full Device Class Name: LTO
Incrementals Since Last Full: 0
Last Complete Backup Date/Time: 12/19/11 07:30:01


How can i increase the cache hit ratio and also what is the location of bufferpoool.....help me

 

[rore]

Hi,
You have to provide more information. It would be easy just to say add more memory, but it is better to understand what really is the problem. To start provide the OS, servers specs, is the server dedicated to TSM?, storage type/layout, and the status of your paging/swap file.

Rudy

 

[Efim]

Hi,
Buffer Pool Hit Ratio was important on TSM till 5.X. from TSM 6.X DB2 use his own memory management mechanism. So I think you must forget about it.


Efim

 

[rore]

Although it is a main performance counter on 5.x I think a value of 31.5 on 6.x requires some attention.
To refresh the concept, from TSM 6.1 Technical Guide:

Buffer Pool Hit Ratio The total hit ratio percent.The ratio of physical reads to logical reads gives the hit ratio for thebuffer pool. The lower the hit ratio, the more the data is being readfrom disk rather than the cached buffer pool which can be a more​

costly operation.


When you did the 'q db f=d', the TSM server was recently restarted?

 

[Efim]

I'll try to explain what I meant.
DB2 adjusts the value of the buffer pool size dynamically. You can't set option BUFPoolsize as you can do it in TSM 5.5. I know 2 ways to increase the Buffer Pool Hit Ratio:
- add more RAM but it is not reasonable because ksc hasn't told about slow TSM performance or high disk I/O.
- wait several days.
Efim

 

[rore]

Yes, BUFPoolsize doesn't exists in TSM 6.x.

Well, before trying to increase the buffer pool hit ratio by no matter which method, I insist let's find out is there is really a problem and what it is.

To start provide the OS, servers specs, is the server dedicated to TSM?, storage type/layout, and the status of your paging/swap file.

 

[ksc]

Firstly thanx for the reply..........

This is a dedicated TSM server.
oslevel is 5.3.0.0.
Memory Size: 15808 MB
Good Memory Size: 15808 MB
Paging Space Information
Total Paging Space: 14848MB
Percent Used: 1%
And vmstat o/p:
kthr memory page faults cpu
----- ----------- ------------------------ ------------ -----------
r b avm fre re pi po fr sr cy in sy cs us sy id wa
1 1 3039087 2455 0 0 0 237 1737 0 895 11131 7289 5 3 88 4

 

[rore]

Well, looks like there is no memory problem on the system. Again, when you did the 'q db f=d', the TSM server was recently restarted?
Is your server doing deduplication?
How many GBs/TBs you backup/archive daily?
Where is sitting the TSM DB? (SAS, FC, SCSI, 10k, 15k, raid?)?

Other than the low hit ration, apparently there is no performance problem, correct?

 

[ksc]

thnx in advance...
TSM server was not recently restarted before running that command.
Daily around 500GB of data will be backed up.
Yes,other than that there is no any issue,but how this bufferpool hit ratio affects the performance?
TSM DB is on FC

 

[rore]

So no apparently issue, nor performance problem. At this point I would call IBM support and ask them if you really have to worry about the low hit ratio. Then, you can maybe share what they said about it in TSM v6.x.

Rudy

 

[ksc]

Thanx alot Rudy....
I would be highly thankful if u call IBM support and get backup to me.

 

[rore]

Sure, send me a PM to coordinate how I should charge you :redface:.