[Why this post: GATHER_SYSTEM_STATS does not gather MREADTIM information from Direct Path Reads]
Oracle can be tuned in a lot of parts and places. One of these is when Oracle is going to choose between reading an index or doing a full table scan.
In this blog I’m not going into depth about all this, but one of the ‘parameters’ here is setting the MREADTIM system statistic to a ‘real life’ value. This value will tell Oracle how fast reading multiple blocks from disk is with all the overhead in between. How many multiple blocks is, is defined by the multi block read count (MBRC) setting. Together with SREADTIM, IOSEEKTIM and MBRC this will have influence in the execution path Oracle will choose.