Is it advisable to use DBCC SHRINK on SAP systems?
After compressing a SAP database many customers find they have a lot of freespace inside the datafiles. However DBCC SHRINKFILE has a very undesirable side effect. SQL Server Page size is fixed at 8KB (unlike Oracle and DB2 where the Page or “Block” size can be changed). A group of 8 x 8KB Pages is arranged into one SQL Extent that is 64K in size. In the example below multiple pages have been written into three Extents. Each letter represents one 8K Page ——– ——– ——– |ABC EF H| |I KLMN P| |QRSTUV X| All pages (and therefore all three extents) belong to the same table. DBCC Shrink will start from the last page in the last extent and work backwards from right to left. Therefore the third extent will be copied to some freespace and the new extent will look like: XVUTSRQ_ with one last empty page in the new extent (the _ means empty) The original pages QRSTUV would have been both physically ordered and logically ordered. After the DBCC Shrink the physical and the logical orde
