Hello,
A few days ago we migrated a DB from 11.2 to 12c (both binaries
on same server, a SuperCluster). We had a query performing fairly good
in the 11g version (around 2 seconds), but after migration to 12c the
response time was very slow (between 25 and 30 seconds) for several days.
In the latter case a select for this statement SQL_ID on IO_CELL_OFFLOAD_ELIGIBLE_BYTES
and IO_CELL_OFFLOAD_RETURNED_BYTES in V$SQL kept showing 0 (zero) and
~ select (1 - (io_interconnect_bytes/NULLIF(physical_read_bytes,0)))*100 "SAVING%"
~ from v$sql [...]
null or negative values.
A few hours later i ran this SELECT again - and now it's blazing fast (result is immediately
returned). In the meantime we did... nothing. Modified nothing, we were simply busy with other
things.
Any idea what had our cells to change their behaviour so dramatically ? (now the "SAVING%" ratio
shown above -that, *if I'm not mistaken*, I took from a Tanel Poder's paper- keeps showing a 99....%
value)
Thanks.
Regards,
Seb