Managing Free Space with Thresholds

When you create or alter a database, you allocate a finite amount of space for its data and log segments. As you create objects and insert data, the amount of free space in the database decreases.

• Monitoring Free Space with the Last-Chance Threshold
  All databases, including master, have a last-chance threshold, which is an estimate of the number of free log pages that are required to back up the transaction log. As you allocate more space to the log segment, SAP ASE automatically adjusts the last-chance threshold.
• Rollback Records and the Last-Chance Threshold
  Rollback records are logged whenever a transaction is rolled back. Servers save enough space to log a rollback record for every update belonging to an open transaction.
• Last-Chance Threshold and User Log Caches for Shared Log and Data Segments
  Every database in an SAP ASE has a last-chance threshold, and all databases allow transactions to be buffered in a user log cache.
• Add Space to the Master Database’s Transaction Log
  When the last-chance threshold on the master database is reached, you can use alter database to add space to the master database’s transaction log.
• Automatically Aborting or Suspending Processes
  By design, the last-chance threshold allows enough free log space to record a dump transaction command. There may not be enough room to record additional user transactions against the database.
• Waking Suspended Processes
  When dump transaction frees sufficient log space, suspended processes automatically awaken and complete.
• Adding, Changing, and Deleting Thresholds
  The database owner or system administrator can create additional thresholds to monitor free space on any segment in the database.
• Creating a Free-Space Threshold for the Log Segment
  When the last-chance threshold is crossed, all transactions are aborted or suspended until sufficient log space is freed.
• Creating Additional Thresholds on Data and Log Segments
  Create free-space thresholds on data segments as well as on log segments.
• Creating Threshold Procedures
  SAP does not supply threshold procedures; create them yourself to ensure that they are tailored to your site’s needs.
• Disabling Free-Space Accounting for Data Segments
  Use the no free space acctg option to sp_dboption to disable free-space accounting on data segments. You cannot disable free-space accounting on the log segment.