You are evaluating the performance of a SQL statement that accesses a very large table.
You run this query:
interconnect bytes returned by smart scan” statistic.
A.
There is a transaction, which committed after the query began, that has modified some of the table blocks,
causing some “cell single block physical reads” to be requested by the database instance, resulting in
additional I/O.
B.
There are chained rows in the table, causing some “single block physical reads” to be requested by the
database instance, resulting in additional I/O.
C.
The table is a hash clustered table, causing “cell multiblock physical reads” to be requested by the database
instance, resulting in additional I/O.
D.
The table is list partitioned, causing “cell list of blocks physical reads” to be requested by the database
instance, resulting in additional I/O.
E.
There is a local index on a list partitioned table on the column used in the WHERE clause, causing “cell list
of blocks physical reads” to be requested by the database instance, resulting in additional I/O.
Explanation:
C: Scan on a clustered table can prevent a Smart Scan from occur.
D: Scan on an index-organized table can prevent a Smart Scan from occur.
Note: The Cell physical IO interconnect bytes returned by smart scan metric shows how many bytes of I/O were returned by a smart scan to the database server.
References: https://uhesse.com/2011/01/19/exadata-part-i-smart-scan/