db file sequential read

This event signifies that the user process is reading a buffer into the SGA buffer cache and is waiting for a physical I/O call to return. A sequential read is a single-block read.

Single block I/Os are usually the result of using indexes. Rarely, full table scan calls could get truncated to a single block call due to extent boundaries, or buffers already present in the buffer cache. These waits would also show up as 'db file sequential read'.

For further information on db file sequential read you can check the following V$SESSION_WAIT parameter columns:

P1 - The absolute file number
P2 - The block being read
P3 - The number of blocks (should be 1)

The dbtuna Wait State report will display a profile of Oracle wait events over time, and will allow you to quickly spot excessive waits.

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