How memory handling in SAP is performed by Qlikview SAPSQLConnector

From version 5.4 there is an input parameter to the SQL connector called BufferPercentage. The default value is 10 (%) if not defined in the connection string:

CUSTOM CONNECT TO Provider=QvSAPConnector.dll;ASHOST=X.X.X.X;SYSNR=XX;CLIENT=XXX;KeepCasing=1;NullDate=1;XUserId=XXX;
XPassword=XXX;BufferPercentage=2";
 
The shared memory buffer used in SAP is called Export/Import. It has a total allocated size ALLOC_SIZE, but since SAP uses some memory itself there is another size called AVAIL_SIZE that is the actual maximum size possible to use, which is less than ALLOC_SIZE. A third value which can be calculated and changes all the time is FREE_SIZE (the current free size of the buffer).
 
If someone tries to use more space than is available in the Export/Import buffer, SAP automatically overwrites the oldest part of the buffer. The intention when using buffer memory is to use memory and then clean up the used memory when ready. The SQL connector works that way. But not all programs does a cleanup, which means that there will be space used which can be overwritten without problems. The risk of using big chunks of the buffer is to overwrite something that is used by another program.
 
In release 5.3 we used 10 % of the value in ALLOC_SIZE.
 
From release 5.4 we took the value in parameter BufferPercentage and tried to use that percentage of AVAIL_SIZE. But we also made a calculation of FREE_SIZE and reduced the % used space if there was not enough free memory.
 
From Release 5.60 SR1 we take the value in parameter BufferPercentage and tries to use that percentage of the calculated FREE_SIZE. However if the resulting space is less than 2 % of AVAIL_SIZE, then we actually use 2 % of AVAIL_SIZE space. In this case we will overwrite some old and not used space.