RE: db_file_multiblock_read_count causing full scans to take longer?

What version? What is your mbrc system stat?

Yes, the higher dbfmbrc should generally improve the speed of full scans, that is assuming that it actually makes a difference in the number of required I/O operations. Often the effective multiblock read size isn't even close to your dbfmbrc setting due to some blocks already being cached, extent boundaries, etc. Are you sure you have the exact same plan for this query before and after the increase in dbfmbrc? Can you share the plans, executions statistics and wait event summary (9i+) from tkprof with both dbfmbrc settings? Be sure to run the trace with WAITS and statistics_level=all.

Regards,
Brandon

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