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тАО09-12-2006 04:01 AM
тАО09-12-2006 04:01 AM
On one our HPUX server,The application team recommends me to change the kernel paramter maxdsiz value to -1 ie it will disable all the limits that allow the system to allocate the memory as it wants.
currently this parameter is set to 2GB and this value is the system maximum allowed for that kernel parameter.
So I would like to know that by changing this parameter to -1 will be useful as the parameter is already set to maximum system value that can be provided ie 2GB.
Rgds,
Ricky
Solved! Go to Solution.
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тАО09-12-2006 04:14 AM
тАО09-12-2006 04:14 AM
Re: Kernel Parameter Change
If this is, in fact, a 64_bit process then you can set maxdsiz_64bit much, much larger. The prudent approach would be to ask the application developers what is the maximum anticipated dynamic memory allocation and set maxdsiz accordingly.
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тАО09-12-2006 04:15 AM
тАО09-12-2006 04:15 AM
Re: Kernel Parameter Change
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тАО09-12-2006 04:54 AM
тАО09-12-2006 04:54 AM
SolutionNow with (a lot of) patches for 11.00 and later, you can change an EXEC_MAGIC executable to add quadrant 3 (up to 2700 megs) and (in 11.11 or later) quadrant 4 (up to 3700 megs). If you are running 11.23, there is a new 32bit executable model (calledd mpas) that you can use in place of all the EXEC_MAGIC, q3p and q4p options. Still, the limit will be about 3700 megs.
Depending on the version of HP-UX you have and the (lack of) patches for SAM, you should be able to set maxdsize to about 3800 megs. If not, try building the kernel manually and setting maxdsiz to 3800 megs. NOTE: maxdsiz_64 *must* be larger than maxdsiz (unless you are running a 32bit version of HP-UX).
Now *ALL* of these limitations totally disappear if you write your applications as 64bit programs. In that case, you would then set maxdsiz_64 to a large value (20Gb? 200Gb?) and let your programmers go wild with malloc calls to grab all that RAM (and swap space).
NOTE: your application programmers need to read the memory mapping details about 32bit programs to get the details needed. I have attached a simple program that can be compiled 5 different ways to demonstrate the maximum memory that can be obtained. Thye comments show the compiler and chatr options.
Bill Hassell, sysadmin
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тАО09-12-2006 05:14 AM
тАО09-12-2006 05:14 AM
Re: Kernel Parameter Change
Your application team are not systems administrators. They need to estimate their memory requirements and let you set your system up appropriately.
Here is a tuning document that actually contains some relavency on the topic:
http://www2.itrc.hp.com/service/cki/search.do?searchString=UPERFKBAN00000726&docType=Security&docType=Patch&docType=EngineerNotes&docType=BugReports&docType=Hardware&docType=ReferenceMaterials&docType=ThirdParty&hpweb_printable=true&searchCrit=allwords&search.x=28&admit=-1335382922+1157656691296+28353475&mode=id&category=c0&search.y=8
The link is problematic today, please be patient with it.
Summary: Don't do it!
SEP
Owner of ISN Corporation
http://isnamerica.com
http://hpuxconsulting.com
Sponsor: http://hpux.ws
Twitter: http://twitter.com/hpuxlinux
Founder http://newdatacloud.com
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тАО09-12-2006 08:29 PM
тАО09-12-2006 08:29 PM
Re: Kernel Parameter Change
Another paramter just recommended for the change is the o_sync_is_o_dsync which has the current value of "0" which is the default and they recommend me to change this value for "1" and I read there is a risk added by changing it to "1"
"Setting o_sync_is_o_dsync to 1 allows the system to convert any open() or fcntl() calls containing an O_SYNC flag into the same call but using the O_DSYNC flag instead. This means that the function returns to the calling process before the file attributes are updated on the disk, thus introducing the risk that this information might not be on the disk if a system failure occurs."
I didnt understand much about the description So can anyone explain me the exact risk involved in changing this parameter "o_sync_is_o_dsync" to 1?and please let me know If I can go ahead with it?
Rgds,
Ricky