Live Cache 7.9 : Data cache Usage 100% even when system not used

[Farid]

Hello,

We are running SAP SCM 7.03/Oracle 11.2 plugged to a Livecache system (MaxDB 7 .9), the hardware is HP-UX ia64.

I am quite new to MaxDB technology.

We have received several complaints over the past weeks, over MaxDB performances.

It turns out that one of the main issue we had was Data cache Usage 100%

So I have increased the value of CacheMemorySize parameter several times, from 32000 to 64000 to 128000

But after a while, the datacache usage hits 100 %, even when there are no users connected, no datalaods from SCM, absolutely no activity,

And the datache usage remains at 100%

Now the current value is : 256000, but I am afraid that it is only a matter of time, before it hist again 100% for no apparent reasons.

I have checked SAP notes database to try to find any guidance, recommendation on the optimal size

of CacheMemorySize , there are several FAQ, several notes detailing database parameters, but I could not find

anything about CacheMemorySize recommended settings

Any help in understanding why the data cache usage remains at 100% even when there is no activity would be really helpful.

Also any recommendation on CacheMemorySize setting would be really appreciated.

Thank you

Best regards

Raoul

[Former Member · Accepted solution]

Hello Raoul,         

liveCache version 7.9 loads the OMS data impictely after restart into the data cache . So you'll see in the DB-Analyzer expert analysis -> Data Cache Usage file that the Data cache is immediately filled up. The column DC_usage tells you the percentage value of the datacache filling level. If all data is filled into the DC and the Usage in percent is lower than 100% - all OMS data can be loaded into the Cache and you have additional free space for SQL data.

The reload mechanism stops when:

1. all OMS data is loaded into the cache

2. the Filling level of 100% is reached

To find out the correct size of the Data Cache you should use the Db-Analyzer data. here the DB-Analyzer tells you if in normal processing the DC hitrate gets lower than 99%. Then a performacne analysis should be started.

There are no commen recommendations for the size of the Datacache. It depends on the SCM applications and the amount of data which has to be processed in the liveCache.

Regards, Christiane

[Former Member]

Hi,

please check notes

Note 1173395 - FAQ: SAP MaxDB and liveCache configuration

Note 1139904 - FAQ: SAP MaxDB/liveCache database parameters

the old name for CacheMemorySize was cache_size.

"When using the SAP liveCache technology, it should be possible to hold all data that is to be processed in the IO buffer cache."

That means, you should have a CacheMemorySize of the size of your (filled) LiveCache database.

So if your LiveCache database is filled with 10 Gb of data, your CacheMemorySize should be 10 GB, at least, too.

Best regards

Christian