Solved

AIX (DSCR) and oracle prefetching

Posted on 2014-01-22
6
1,270 Views
Last Modified: 2014-01-22
what is AIX (DSCR) prefetching and how it works with Oracle?
our prod DB is showing:
dscrctl -q
Current DSCR settings:
        Data Streams Version  = V2.06
        number_of_streams     = 12
        platform_default_pd   = 0x4 (DPFD_MEDIUM)
       os_default_pd         = 0x0 (DPFD_DEFAULT)

what does this mean?
0
Comment
Question by:it-rex
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 3
  • 3
6 Comments
 
LVL 68

Accepted Solution

by:
woolmilkporc earned 500 total points
ID: 39801187
Hi,

DSCR is hardware memory prefetch. It sometimes can improve the performance of applications, if they reference memory sequentially.

Oracle does not often perform sequential memory access, in fact Oracle's memory access is said to be "irregular", so aggressive prefetching can have an adverse effect on performance because the prefetched lines might not be referenced. Your setting is not very aggressive, though.

I must admit that I'm not a true Oracle tuning specialist, so be careful with the following.

If you're currently experiencing bad performance you could run this command

dscrctl -b -n -s 1

which will turn off memory prefetching (-b = persist across reboots, -n = apply changes immediately, -s 1 = set the dscr value to 1, which is DFPD_NONE).
Please watch the DB very thoroughly for the effect of this setting, and should you see a decrease in performance turn prefetching on again with

dscrctl -b -n -s 0

which will go back to your defaults.

wmp
0
 
LVL 11

Author Comment

by:it-rex
ID: 39801230
so what is the difference between
 os_default_pd         = 0x0 (DPFD_DEFAULT)
and the default of
 os_default_pd         = 0x5 (DPFD_DEFAULT)

?
0
 
LVL 11

Author Comment

by:it-rex
ID: 39801242
Sir..
Also i'm posting few AIX specific Q's and I really like to see your input about them..
0
Independent Software Vendors: We Want Your Opinion

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

 
LVL 68

Expert Comment

by:woolmilkporc
ID: 39801328
0x0 sets os_default to platform_default, which is 0x4 DPFD_MEDIUM fot the machine shown in your question.

0x5 is not DPFD_DEFAULT, and also not platform_default, at least not on the machine you showed in your Q. There are machines whose platform_default is 0x5, but DFPD_DEFAULT is always 0x0!
0x5 is DFPD_DEEP, which is more aggressive than DPFD_MEDIUM
0
 
LVL 11

Author Comment

by:it-rex
ID: 39801351
so what do you suggest here?
0
 
LVL 68

Expert Comment

by:woolmilkporc
ID: 39801371
Leave it at 0x0 (the default which is DFPD_MEDIUM in your case) or turn it off according to my first comment - please read it again - in full!
0

Featured Post

Enroll in June's Course of the Month

June's Course of the Month is now available! Every 10 seconds, a consumer gets hit with ransomware. Refresh your knowledge of ransomware best practices by enrolling in this month's complimentary course for Premium Members, Team Accounts, and Qualified Experts.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Hello fellow BSD lovers, I've created a patch process for patching openjdk6 for BSD (FreeBSD specifically), although I tried to keep all BSD versions in mind when creating my patch. Welcome to OpenJDK6 on BSD First let me start with a little …
In tuning file systems on the Solaris Operating System, changing some parameters of a file system usually destroys the data on it. For instance, changing the cache segment block size in the volume of a T3 requires that you delete the existing volu…
Learn several ways to interact with files and get file information from the bash shell. ls lists the contents of a directory: Using the -a flag displays hidden files: Using the -l flag formats the output in a long list: The file command gives us mor…
Learn how to find files with the shell using the find and locate commands. Use locate to find a needle in a haystack.: With locate, check if the file still exists.: Use find to get the actual location of the file.:

696 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question