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db file scattered read

Short Description

Similar to db file sequential read, except that the session is reading multiple data blocks.

Detailed Description​

Simplification: this is a Multi-block Read. Yes it's confusing - we know but in this case the multiple disk blocks are read and scattered into memory concurrently. This method is used in full table scans and full fast index scans and is generally a faster way of reading data than a db file sequential read . The number of blocks read at one time is controlled by the parameter db_file_multiblock_read_count

How to reduce this wait​

It is normal to see these waits in your system. Tuning is carried out in two ways:

  1. Tuning your SQL queries to use the most efficient access path.

  2. Tuning the db_file_multiblock_read_count parameter to minimise the number of IO operations.

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