Date: Mon, 29 Sep 2008 20:25:15 -0500 (CDT)
The writes will not cross extent boundaries so if you use AUTOALLOCATE for extent management and it starts with 64K extents then that is all that will be returned in a single read. Once the extent size reaches 1M or larger then it's not an issue.
> I have always been a little humored by this parameter.
> db_file_multiblock_read_count attempts to specify a maximum value, as does
> the MBRC collected by system stats. However, that does not determine how
> many blocks are actually scooped up in a multiblock pass. One good example
> is to set event 10046 on a full table scan with waits (level 8 or 12) and
> look for db file scattered read waits, which will have the number of blocks
> read during the wait.