Adaptive Server’s transaction log is a special heap table that stores information about data modifications in the database. The transaction log is always a heap table; each new transaction record is appended to the end of the log. The transaction log does not have any indexes.
Other chapters in this book describe ways to enhance the performance of the transaction log. The most important technique is to use the log on clause to create database to place your transaction log on a separate device from your data.
See the System Administration Guide for more information on creating databases.
Transaction log writes occur frequently. Do not let them contend with other I/O in the database, which usually happens at scattered locations on the data pages.
Place logs on separate physical devices from the data and index pages. Since the log is sequential, the disk head on the log device rarely needs to perform seeks, and you can maintain a high I/O rate to the log.
Besides recovery, these kinds of operations require reading the transaction log:
Any data modification that is performed in deferred mode.
Triggers that contain references to the inserted and deleted tables. These tables are built from transaction log records when the tables are queried.
Transaction rollbacks.
In most cases, the transaction log pages for these kinds of queries are still available in the data cache when Adaptive Server needs to read them, and disk I/O is not required.
