Manage Transactions and Versioning

Transaction processing ensures that logically related groups commands execute as a unit. SAP Sybase IQ uses transaction processing to allow many users to read from the database while it is being updated. Transactions are fundamental to maintaining the accuracy of your data, and to data recovery in the event of system failure.

A crucial aspect of transaction processing is its ability to isolate users from the effect of other users' transactions. The SAP Sybase IQ approach to transaction processing, called snapshot versioning, supports the highest level of isolation recognized by ISO. Snapshot versioning provides each database user with a snapshot of the database. Any changes that you make to the database are not seen by other database users until you commit your transaction.

• Transactions
  Each transaction is a sequence of logically related commands that accomplish one task and transform the database from one consistent state into another.
• Transaction Blocking
  When you set the BLOCKING option to on, any transaction attempting to obtain a write lock that conflicts with an existing write lock held by another transaction waits until the conflicting lock is released, or until the BLOCKING_TIMEOUT threshold is reached. By default, BLOCKING is off.
• Versions
  The database server binds the snapshot version when a transaction is created, after the transaction has obtained the necessary write locks on the table or the table row. Table-level versioning enables single-writer access and table-level locking. Row-level versioning (RLV) enables concurrent writer access and row-level locking for RLV-enabled tables.
• Investigating Lock Contention Effects on Performance
  Some load or query performance issues result from lock contention. If your kernel system time is greater than 10%, you may be experiencing lock contention.
• Checkpoints, Savepoints, and Transaction Rollback
  Besides permitting concurrency, snapshot versioning transaction processing plays an important role in data recovery.
• Cursors in Transactions
  Return the results of a SELECT in the form of a data type called a cursor.
• Remote Transactions
  Transaction management involving remote servers uses a two-phase commit protocol.