Waits on this event indicate the statement is performing a full table scan or an index range scan. This is often reduced by adding an index or making the index more efficient. Solutions Tune the SQL statement so that it uses an index rather than a full table scan if warranted. If the table is small, a full table scan could be more efficient that using an index so test the differences. Use the Ignite Objects tab to determine the most costly full table scan if there are more than one table in the query. Increase the buffer cache so that more blocks are already in memory rather having to be read from disk. The query will still need to read the same number of blocks so tuning is the first recommendation, but if you cannot tune the statement, a query reading blocks from memory is much faster than from disk. Slow disks could be causing Oracle to spend time reading the data into the buffer cache. Review the 'DB Multi Block Disk Read Time' metric in Ignite to determine disk speeds from Oracle's perspective. If the time to read data is above 30ms, that could indicate slow disks. Update table and index statistics if they are stale so that Oracle understands the benfits of existing indexes.
本文转自maclean_007 51CTO博客，原文链接:http://blog.51cto.com/maclean/1277908
