Memory Distribution for SAP, Windows 2003 and SQl 2005
We are running on 64bit Server Windows 2003 Enterprise Edition, SQL 2005, ECC 6.0 ABAP only.
Physical memory size = 32GB.
Current PHY_MEM setting = 19GB
SQL is allocalted fixed 13 GB.
Swap or Virtucal memory - 60GB.
I am not sure, if Zero memory management allows Windows Operating system to gain mamory automatically ? or should I correct some settings in SAP Memory or SQL memory to allow OS to gain some physical memory ?
Markus Doehr replied
b. With Respect to SQL Memory allocation, as mentioned earlier, we have allocated some fixed 12.9GB. and ST04 report shows, Data cache used up to 7.6GB, Proc Cache used 2.6 GB and log size allocated it self 5.8 GB. We are getting occational alerts that DB buffer hit ratio has fallen below 80%, dows this mean, data cache is over writing itself when it used up its maximum ?
Yes - exactly.
DB buffer hit ratio 100 % means: All the requested data was in the cache. If more data is read, the pages, that have not been accessed for a long time, are displaced by others. The best performance is reached, if your data cache hit ration doesn´t go down to more than 95 %. If it does, then your cache/buffer is too small or someone executed a HUGE report displacing all the "valid" data and hence slowing down the system.
c. Regarding the flat memory model configuration, the following discussion says there is no real advantage and the note says it uses more memory and less CPU power. We have 16 CPUs, so we we really find any advantage ? I know you are just suggesting and not reccomonding, I am keen on your comments.
That is an interesting statement.
The absolute CPU power is not significant in that area, it´s the number of "CPU cycles" that are used during context switches are, which are done by one CPU at a time no matter how many of them you have. If you switch to flat memory model, you will see a decrease of kernel time in the task manager graph (the "red" part if you switch it on).
However, since your system doesn´t seem to be a very very high loaded system and is not virtualized you can use the traditional/default memory model.