SAP DB Interview Questions and Answers
Question - 91 : - How Are Locks On Joins Handled?
Answer - 91 : -
The SQL locks on joins are handled in the same way as locks on tables. There is no difference.
Question - 92 : - Is A Shared Lock Assigned To Each Data Record Of The Table During A Full Table Scan As Long As The Query Is Running?
Answer - 92 : -
In isolation level 1, a lock is temporarily used for each record and is removed before the next record.
In isolation level 3, a table shared lock is used.
Question - 93 : - When Should You Increase The Database Parameter Maxsqllocks (maxlocks)?
Answer - 93 : -
MaxSQLLocks values that are too high result in long search processes in the lock lists. Therefore, if this is possible, reduce the write transactions by using frequent commits.
You can increase MaxSQLLocks if one of the following situations frequently occur:
- There is a high number of LOCK LIST ESCALATIONS
- the number of LOCK LIST MAX USED ENTRIES equals the value of MaxSQLLocks.
- The number of LOCK LIST MAX USED ENTRIES is close to the value of MaxSQLLocks and the write transactions cannot be reduced.
Question - 94 : - What Does The Following Sql Error -1000 Mean: Too Many Lock Requests?
Answer - 94 : -
A transaction terminates because too many SQL locks were requested. The configured maximum value (MaxSQLLocks) has been reached. The system can assign no further SQL locks.
If these problems frequently occur in the system, check the value of the database parameter MaxSQLLocks.
Question - 95 : - Does The Sap Maxdb Use Consistent Reading?
Answer - 95 : -
Consistent reading has not been supported yet in the OLTP operation and OLAP operation. The lock management of SAP MaxDB will be changed in more current versions due to the MVCC implementation. Currently, we cannot specify in which SAP MaxDB version this function can be used productively.
Question - 96 : - What Is The Isolation Level?
Answer - 96 : -
The isolation level defines whether and in which way locks are implicitly requested or d.
The selected isolation level affects the degree of parallelism of concurrent transactions and the data consistency:
The lower the value of the isolation level, the higher the degree of parallelism and the lower the degree of the guaranteed consistency.
If there are concurrent accesses to the same dataset, various inconsistencies (such as dirty read, non-repeatable read, and phantom) may occur at different isolation levels.
For SAP applications (ABAP stack), the isolation level is defined in the XUSER file. The ABAP applications run at isolation level 0.
In NetWeaver (Java stack), data sources are used for the application logon. These data sources can be configured using the NetWeaver. You can freely choose the isolation level. If the data source does not specify an explicit isolation level, default isolation level 1 (read committed) is used.
Question - 97 : - What Is An Exclusive Lock?
Answer - 97 : -
If an exclusive lock on a database object is assigned to a transaction, other transactions cannot access this object.
Transactions that want to check whether exclusive locks exist or to set exclusive or shared locks collide with the existing exclusive lock of the other transaction. They cannot access the locked object.
Exclusive locks can be set on individual table lines or on the entire table.
Question - 98 : - What Is A Shared Lock?
Answer - 98 : -
Shared locks allow other transactions to perform read accesses but not to perform write accesses to the locked object. Other transactions can set further shared locks on this object, but no exclusive locks.
Shared locks can be set on individual table lines or on the entire table.
Question - 99 : - What Is A Parallel Index Build?
Answer - 99 : -
The data for the index is read in parallel by several server tasks to perform the index build as quickly as possible. Only one parallel index build can be carried out at a time - if several CREATE INDEX statements are executed at the same time, these other indexes are then processed by only one server task. This is noticeably slower than a parallel index build. Therefore, you should always ensure that indexes are only created successively.
Question - 100 : - Why May It Take A Long Time Until A Task Is Available Again After You Cancel The User Task To Cancel The Creation Of An Index?
Answer - 100 : -
If you cancel a CREATE INDEX statement, the cancel indicator is set for the user task. However, before the task can be re-released, it must clear all index lists that were created before by the server tasks for the index build.
This ensures that all of the structures that are no longer required are deleted from the system after you cancel a CREATE INDEX statement. This may take some time depending on the number and size of the index lists.