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Database Administration
Maintaining and Monitoring Your Database : Managing Performance : Server performance factors : After-image I/O : Using an after-image writer
 
Using an after-image writer
The AIW is a background process that writes AI buffers to disk soon after they are filled. If the AIW is working effectively, client and server processes rarely have to wait for a modified buffer to be written to disk.
The AI buffer pool is a circular chain of buffers. The database engine fills these buffers one at a time. The buffer that the engine fills at any time is the current output buffer. As each buffer is filled, the engine continues around the chain, and each buffer in turn becomes the current output buffer. If the next buffer to write is already modified, the engine must wait while that buffer is written to disk.
You can run only one AIW process per database at a time. You must manually start the AIW, but you can start and stop an AIW at any time without shutting down the database. See Starting Up and Shutting Down for instructions on starting and stopping an AIW.
Increasing the -aibufs startup parameter increases the number of buffers in the after-image buffer pool, which increases the availability of empty buffers to client and server processes. Set the -aibufs parameter to 1.5 times the value of the Before-image Buffers (-bibufs) parameter. (For information on setting the -bibufs parameter, see Providing more BI buffers .) Increasing -aibufs has no effect if the AIW is not running.