As with before-imaging, the database engine reads and writes information to the AI file in blocks. Increasing the size of AI blocks lets the engine read and write more AI data at one time. This can reduce I/O rates on disks where the AI files are located. In general, the default AI block size (8K) is sufficient for systems with low transaction rates. However, if performance monitoring indicates that AI writes are a performance bottleneck and your platform's I/O subsystem can take advantage of larger writes, increasing the AI block size might improve performance. A larger AI block size might also improve performance for roll-forward recovery processing.
To change the AI block size:
1. Use the PROSHUT command or the PROMON Shutdown a Database option to shut down the database.
2. If after-imaging is enabled, disable it by entering the following command:
rfutil db-name -C aimage end
For more specific information on this command, see the description of the RFUTIL utility AIMAGE END qualifier in RFUTIL Utility.
3. Truncate the BI file to bring the database and BI files up to date and eliminate any need for database recovery. To do this, enter the following command:
Typically, if you change the AI block size, you should also change the BI block size. If you have not already, you might want to use this command to do so. For more information on the BI block size, see Increasingthe BI block size.
4. Change the AI block size by entering the following command:
rfutil db-name -C aimage truncate -aiblocksize size[ -a aifilename]
For size, specify the size of the AI read and write block in kilobytes. The minimum value allowed is the size of the database block. Valid values are 0, 1, 2, 4, 8, and 16. If you specify 0, RFUTIL uses the default size (8K) for your operating system platform.
5. Perform a full backup of the database.
Note: You must perform this step because backups and AI files created before you change the AI block size are no longer valid with the new AI block size. For detailed backup instructions, see BackingUp a Database.
6. Enable after-imaging by entering the following command:
rfutil db-name -C aimage begin { buffered | unbuffered } -a ai-name
For more specific information on this command, see RFUTIL Utility.
