When the database server processes a transaction, it can lock one or more table rows. The locks maintain the reliability of information stored in the database by preventing concurrent access by other transactions. They also improve the accuracy of result queries by identifying information that is in the process of being updated.
The database server places these locks automatically and needs no explicit instruction. It holds all the locks acquired by a transaction until the transaction is completed. The transaction that has access to the row is said to hold the lock. Depending on the type of lock, other transactions may have limited access to the locked row, or none at all.
Performance can be compromised if a row or rows are frequently accessed by several users simultaneously. If you suspect locking problems, consider using the sa_locks procedure to obtain information about locks in the database.
If lock issues are identified, information about the connection processes involved can be found using the AppInfo connection property.
Discuter à propos de cette page dans DocCommentXchange.
|Copyright © 2013, SAP AG ou société affiliée SAP - SAP Sybase SQL Anywhere 16.0|