Re: DB Cache Hit Rate Question
Can anybody tell me where I can locate a copy of the TSM 3.7 Technical Ref Redbook. I assume it is a seperate entity to the Admin Guide and Admin Reference. Thanks Farren Minns John Wiley Sons Ltd Please respond to ADSM: Dist Stor Manager [EMAIL PROTECTED] Sent by: ADSM: Dist Stor Manager [EMAIL PROTECTED] To: [EMAIL PROTECTED] cc: Subject: Re: DB Cache Hit Rate Question I'm a little confused about the cache hit ratio information. If I run expiration on a database, surely the TSM server has to trawl through the entire thing on disk as it does not already reside in the buffer. So how would I expect to see hit ratios of 99% or higher. I won't go into details here as I'm more interested in the process of how the database and cache work than out particular performance problems. But, as we do very little in the way of restores, surely the amount of time that a requested database file is present in the cache must be very low, so a cache hit ratio of 96-98% would make sense. Farren - If you have not yet delved into the TSM Technical Guide redbooks, you will find them excellent reading, particularly as they serve as a record of the evolution of the product. The TSM 3.7 Technical Guide in particular talks about the buffer pool size and use of Expiration as a self-tuning measure. Richard Sims, BU (home shoveling today)
Re: DB Cache Hit Rate Question
Hi Farren! Is this the manual you are looking for? http://publib-b.boulder.ibm.com/Redbooks.nsf/9445fa5b416f6e32852569ae006bb65 f/ede73841f6c641108525676a00536b23?OpenDocument Kindest regards, Eric van Loon KLM Royal Dutch Airlines -Original Message- From: Farren Minns [mailto:[EMAIL PROTECTED]] Sent: Wednesday, February 19, 2003 11:15 To: [EMAIL PROTECTED] Subject: Re: DB Cache Hit Rate Question Can anybody tell me where I can locate a copy of the TSM 3.7 Technical Ref Redbook. I assume it is a seperate entity to the Admin Guide and Admin Reference. Thanks Farren Minns John Wiley Sons Ltd Please respond to ADSM: Dist Stor Manager [EMAIL PROTECTED] Sent by: ADSM: Dist Stor Manager [EMAIL PROTECTED] To: [EMAIL PROTECTED] cc: Subject: Re: DB Cache Hit Rate Question I'm a little confused about the cache hit ratio information. If I run expiration on a database, surely the TSM server has to trawl through the entire thing on disk as it does not already reside in the buffer. So how would I expect to see hit ratios of 99% or higher. I won't go into details here as I'm more interested in the process of how the database and cache work than out particular performance problems. But, as we do very little in the way of restores, surely the amount of time that a requested database file is present in the cache must be very low, so a cache hit ratio of 96-98% would make sense. Farren - If you have not yet delved into the TSM Technical Guide redbooks, you will find them excellent reading, particularly as they serve as a record of the evolution of the product. The TSM 3.7 Technical Guide in particular talks about the buffer pool size and use of Expiration as a self-tuning measure. Richard Sims, BU (home shoveling today) ** For information, services and offers, please visit our web site: http://www.klm.com. This e-mail and any attachment may contain confidential and privileged material intended for the addressee only. If you are not the addressee, you are notified that no part of the e-mail or any attachment may be disclosed, copied or distributed, and that any other action related to this e-mail or attachment is strictly prohibited, and may be unlawful. If you have received this e-mail by error, please notify the sender immediately by return e-mail, and delete this message. Koninklijke Luchtvaart Maatschappij NV (KLM), its subsidiaries and/or its employees shall not be liable for the incorrect or incomplete transmission of this e-mail or any attachments, nor responsible for any delay in receipt. **
Re: DB Cache Hit Rate Question
Can anybody tell me where I can locate a copy of the TSM 3.7 Technical Ref Redbook. I assume it is a seperate entity to the Admin Guide and Admin Reference. Farren - Yes... All redbooks are separate from the main manuals. The redbooks are at http://www.redbooks.ibm.com . There, you would search on technical guide. For basic questions, see http://people.bu.edu/rbs/ADSM.QuickFacts . Here is an extract from that area of interest: Redbooks and Redpieces of note (at www.redbooks.ibm.com): Getting Started with Tivoli Storage Manager: Implementation Guide (SG24-5416) (Includes performance tuning info) http://www.redbooks.ibm.com/abstracts/sg245416.html http://www.redbooks.ibm.com/redbooks/SG245416.html http://www.redbooks.ibm.com/pubs/pdfs/redbooks/sg245416.pdf Tivoli Storage Management Concepts (SG24-4877) http://www.redbooks.ibm.com/abstracts/sg244877.html http://www.redbooks.ibm.com/redbooks/SG244877.html http://www.redbooks.ibm.com/pubs/pdfs/redbooks/sg244877.pdf Tivoli Storage Management Reporting http://www.redbooks.ibm.com/abstracts/sg246109.html ADSM Version 3 Technical Guide http://www.redbooks.ibm.com/abstracts/sg242236.html http://www.redbooks.ibm.com/redbooks/SG242236.html http://www.redbooks.ibm.com/pubs/pdfs/redbooks/sg242236.pdf Tivoli Storage Manager Version 3.7.3 4.1 Technical Guide http://www.redbooks.ibm.com/abstracts/sg246110.html http://www.redbooks.ibm.com/redbooks/SG246110.html http://www.redbooks.ibm.com/pubs/pdfs/redbooks/sg246110.pdf Tivoli Storage Manager Version 4.2 Technical Guide http://www.redbooks.ibm.com/abstracts/sg246277.html http://www.redbooks.ibm.com/redbooks/SG246277.html http://www.redbooks.ibm.com/pubs/pdfs/redbooks/sg246277.pdf Tivoli Storage Manager Version 5.1: Technical Guide (SG24-6554) http://www.redbooks.ibm.com/abstracts/sg246554.html http://www.redbooks.ibm.com/redbooks/SG246554.html http://www.redbooks.ibm.com/pubs/pdfs/redbooks/sg246554.pdf Richard Sims, BU
Re: DB Cache Hit Rate Question
OK, all the info I have received has been of great help and indeed the Technical Reference guide is very informative. But what I still don't understand is this. I'm running expiration on the db at the moment and the cache hit it average at 98.5%. Not 99%, but not too bad. But the rest of the time, i.e. when running backups etc, it drops to as low as 95%. Should the cache hit rate consistently be above 98%? This is the answer I cannot find. Many thanks again to all who have provided help with this. Farren Minns - John Wiley Sons Please respond to ADSM: Dist Stor Manager [EMAIL PROTECTED] Sent by: ADSM: Dist Stor Manager [EMAIL PROTECTED] To: [EMAIL PROTECTED] cc: Subject: Re: DB Cache Hit Rate Question Farren, I'm not sure exactly how the TSM database internals work, but typically a database cache is populated with cache prefetch. This isn't _exactly_ correct, but it'll do conceptually. The db goes to read one row (check a file for expiration). That one db row request loads one or more blocks/pages of db into the cache. Those blocks contain many other rows, so most of the next few thousand file checks get cache hits in the prefetched cached blocks. Hope this helps. Alex Paschal Freightliner, LLC (503) 745-6850 phone/vmail -Original Message- From: Farren Minns [mailto:[EMAIL PROTECTED]] Sent: Tuesday, February 18, 2003 8:25 AM To: [EMAIL PROTECTED] Subject: DB Cache Hit Rate Question Good afternoon all TSMers. I'm a little confused about the cache hit ratio information. If I run expiration on a database, surely the TSM server has to trawl through the entire thing on disk as it does not already reside in the buffer. So how would I expect to see hit ratios of 99% or higher. I won't go into details here as I'm more interested in the process of how the database and cache work than out particular performance problems. But, as we do very little in the way of restores, surely the amount of time that a requested database file is present in the cache must be very low, so a cache hit ratio of 96-98% would make sense. Please forgive my ignorance here as I'm not a expert in this field at all. Many thanks in advance All the best Farren Minns John Wiley Sons Ltd
Re: DB Cache Hit Rate Question
...Should the cache hit rate consistently be above 98%? ... In a single word: No. The 99%+ is the fairy tale objective. You'll find numerous postings in the List archives advising of the real world behavior of caches which, as you've seen with Backups, cause the number to drop, as one should expect with a large number of such unique accesses. The best we can do is dedicate as much *real* memory as feasible to maximize the number during steady-state operations. Don't get over-absorbed in Cache Hit Ratio: It's just one factor among the many that a systems person has to address to maximize server throughput. Your time needs to go into a lot of other issues as well. Richard Sims, BU
Re: DB Cache Hit Rate Question
I'm a little confused about the cache hit ratio information. If I run expiration on a database, surely the TSM server has to trawl through the entire thing on disk as it does not already reside in the buffer. So how would I expect to see hit ratios of 99% or higher. I won't go into details here as I'm more interested in the process of how the database and cache work than out particular performance problems. But, as we do very little in the way of restores, surely the amount of time that a requested database file is present in the cache must be very low, so a cache hit ratio of 96-98% would make sense. Farren - If you have not yet delved into the TSM Technical Guide redbooks, you will find them excellent reading, particularly as they serve as a record of the evolution of the product. The TSM 3.7 Technical Guide in particular talks about the buffer pool size and use of Expiration as a self-tuning measure. Richard Sims, BU (home shoveling today)
Re: DB Cache Hit Rate Question
Farren, I'm not sure exactly how the TSM database internals work, but typically a database cache is populated with cache prefetch. This isn't _exactly_ correct, but it'll do conceptually. The db goes to read one row (check a file for expiration). That one db row request loads one or more blocks/pages of db into the cache. Those blocks contain many other rows, so most of the next few thousand file checks get cache hits in the prefetched cached blocks. Hope this helps. Alex Paschal Freightliner, LLC (503) 745-6850 phone/vmail -Original Message- From: Farren Minns [mailto:[EMAIL PROTECTED]] Sent: Tuesday, February 18, 2003 8:25 AM To: [EMAIL PROTECTED] Subject: DB Cache Hit Rate Question Good afternoon all TSMers. I'm a little confused about the cache hit ratio information. If I run expiration on a database, surely the TSM server has to trawl through the entire thing on disk as it does not already reside in the buffer. So how would I expect to see hit ratios of 99% or higher. I won't go into details here as I'm more interested in the process of how the database and cache work than out particular performance problems. But, as we do very little in the way of restores, surely the amount of time that a requested database file is present in the cache must be very low, so a cache hit ratio of 96-98% would make sense. Please forgive my ignorance here as I'm not a expert in this field at all. Many thanks in advance All the best Farren Minns John Wiley Sons Ltd
