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A good place to look is V$SQLFN_METADATA.
The “OFFLOADABLE” column is relatively self-explanatory. Here are some general rules off cell offload eligibility:
The IO savings for offload processing is proportional to the aggregate function used in some cases.
I’ll provide examples below:
The above is offload-able, yielding a dramatic savings in IO.
Eligible for offload due to column filtering, not-so-dramatic savings.
Even though we manually selected all columns had had no predicate, Exadata marks this offload eligible. I believe this is due to row reduction caused by “select count(1)” wrapper around it but let’s test this theory:
This looks to have had the same effect. Let’s try this using PL/SQL so we can actually do a “SELECT *” without having to worry about wading through a ton of output:
In this example, the SQL was marked offload-eligible but in fact only a very small amount was offloaded. This is contrary to Oracle documentation (and not necessarily a bad thing), but perhaps due to the fact that SOE.ORDERS is partitioned. Let’s try the same test on a 150 million row non-partitioned table:
And we see the same result – interesting.
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