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Don Burleson Blog 







Using _db_file_noncontig_mblock_read_count

Oracle Database Tips by Donald BurlesonApril 16, 2015


Tuning multi-block reads was quite challenging before the 10gr2 automatic setting for multi-block reads (sequential pre-fetch for full-table scans).  See Automatically tuned multi-block reads in 10g.  However, Oracle still has some hidden parameters that influence the  multi-block read mechanism, including the undocumented _db_file_noncontig_mblock_read_count initialization parameter, which is related to db_file_multiblock_read_count.

Starting in Oracle 8.1.5, the _db_file_noncontig_mblock_read_count parameter controls the  maximum number of blocks to be prefetched in one batch. If set to 1, prefetching should be disabled.  Also, see these notes on the latest consensus on multiple blocksizes.

Never use this undocumented parameter without the expressed consent of Oracle technical support, and see my related notes on tuning multi-block disk reads:


If you like Oracle tuning, you might enjoy my book "Oracle Tuning: The Definitive Reference", with 950 pages of tuning tips and scripts. 

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.



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