[IQUG] Memory sizing in IQ

Mumy, Mark mark.mumy at sap.com
Wed May 1 07:25:03 MST 2013


What is it that you are asking to "fix"?  I am not sure I understand what the question is.


Mark Mumy, Technical Director, Enterprise Systems Group, SAP
M +1 347-820-2136 | E mark.mumy at sap.com<mailto:mark.mumy at sap.com>

Conference tel: 18663127353,,7090196396#

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From: iqug-bounces at iqug.org [mailto:iqug-bounces at iqug.org] On Behalf Of Rey
Sent: Wednesday, May 01, 2013 9:20 AM
To: iqug at iqug.org; Louie, David
Subject: Re: [IQUG] Memory sizing in IQ

This is bad, I saw something weird at my system. Our temp store is 2-3 times bigger than temp cache.
Is it hardware sizing guide should mention this with more test benchmarks?

I doubt we will upgrade to IQ 16 shortly, can SAP fix this at IQ 154 level?

On 4/30/2013 12:41 PM, Louie, David wrote:
Check to see if your IQ temp cache is close to your IQ temp store size.    We had our IQ temp cache over allocated at 450 GB when our IQ temp store was only 100 GB.  We were advised by Mark Mumy that IQ temp cache is written to both IQ temp store and IQ temp cache at the same time ( he indicates this behavior may change in 16).  We've reduced our IQ temp cache to 150 GB which is closer to our 100 GB of IQ temp store and allocated that RAM back to main cache.  As expected we have seen a tremendous reduction in IO since increasing the main cache.


From: iqug-bounces at iqug.org<mailto:iqug-bounces at iqug.org> [mailto:iqug-bounces at iqug.org] On Behalf Of Macalalad, Jun
Sent: Tuesday, April 30, 2013 9:51 AM
To: Ron Watkins; 'Toni Berry'; 'IQ Users Group'
Subject: Re: [IQUG] Memory sizing in IQ

Does this mean that IQ needs to be by itself in a host server - without Informatica/Business Objects with SQL Server repository? Else it will starve others of resources hence require restart (of IQ or the host) more often?  Sorry if I am painting a grim picture --- resource-wise ...


From: iqug-bounces at iqug.org<mailto:iqug-bounces at iqug.org> [mailto:iqug-bounces at iqug.org] On Behalf Of Ron Watkins
Sent: Tuesday, 30 April 2013 9:17 PM
To: 'Toni Berry'; 'IQ Users Group'
Subject: Re: [IQUG] Memory sizing in IQ

There is never any problem with over allocating cache. I believe the sizing guide is based on an cost-benefit model.

You should see some performance benefit, although I cannot say how much that will be exactly.
In theory, you could allocate as much cache as the size of your data, in which case once the data was initially pulled into cache it would stay there and IQ would effectively have its entire store in cache.
I believe the sizing guide is based on an cost-benefit model.

As for the utilization, main cache will start at 0% and grow as data is pulled in from disk. Since data is never removed unless the space is needed for another object, it will grow to 100% and stay there. That is normal. The rule for main cache is to remove data only when the pages are needed by another object. I believe it uses an algorithm called Least-Recently-Used, so when IQ replaces pages in cache with other objects, it will choose the least recently used object to remove. There is no reason to forcibly remove data from cache in normal operations, so that is why it will stay at 100% untill a restart occurs.

Temp cache is different in that an object there only exists as long as the connection is making use of that object. When the connection goes away, the space associated with that connection is dropped, thus freeing up TEMP cache. This is why you should see TEMP cache fluctuate whereas MAIN cache stays at 100%.

From: iqug-bounces at iqug.org<mailto:iqug-bounces at iqug.org> [mailto:iqug-bounces at iqug.org] On Behalf Of Toni Berry
Sent: Tuesday, April 30, 2013 1:03 AM
To: IQ Users Group
Subject: [IQUG] Memory sizing in IQ

Hi All,

In the Sybase IQ 15 sizing Guide white paper, the general memory guideline is 4-8GB per core.  As we have a 4-core configuration we allocate 22GB to Sybase IQ, so this configuration meets the general guideline of sizing between 16-32GB.

The server that host our Sybase IQ instance will gain more RAM, so I'm looking at allocating Sybase IQ around 32GB RAM.
I have the opportunity to raise the allocation to 48GB for Sybase IQ  (Say a split of IQ main cache 30GB, IQ Temp Cache 18GB).

My question is there any significant performance gains allocating more memory than what is in the general guideline?

With our 22GB allocation, IQ Main cache (12GB) is always 100% utilised, whereas IQ Temporary Cache (10GB) varies depending on activity though rarely at 100%

Regards,   Toni.
Toni Berry
Apps Support Team Leader - Data Warehouse
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