Spotlight on DB2 6.10 - User Guide

Synchronous Index Reads

Reads that retrieve index pages from the database into buffer pools as part of query processing. Synchronous index reads occur when a query requires an index page that is not already in the buffer pool. The system must read these pages from disk into the buffer pool before execution of the query can continue.

Compare synchronous index reads with asynchronous index reads, in which prefetchers read index pages from the database into the buffer pool before these pages are actually needed by the query. These reads are asynchronous because they are performed outside of actual query processing. Asynchronous reads do not block query processing while index pages are retrieved.