Storage indexes are unique to the Exadata Database Machine and their primary goal is to reduce the amount of I/O required to service I/O requests for Exadata Smart Scan. Put the following steps in order:
1. The Exadata cell services software conducts I/O requests on I MO storage regions.
2. cellsrv checks the high and low values, and determines the storage region does not contain any values meeting the predicate.
3. The database is started.
4. Physical I/O to the region is bypassed if the query selection falls outside the high/low storage index storage.
5. A query is issued against the MYOBJ_CTRL table that has a predicate OBJECT_ID=1500.
6. A subsequent query is Issued against the MYOBJ_CTRL table that has a predicate OBJECT_ID=2234.
7. MYOBJ_STATE’S region index is populated with high and low values for the OBJECT_ID column during the I/O request.
A. 3. 7, 5, 2, 1, 6, and 4
B. 3, 7, 1, 5, 6, 2, and 4
C. 3, 6, 1. 7, 2, 5 and 4
D. 3, 5, 1, 7, 6, 2. and 4
Correct Answer: D
Explanation/Reference:
3. The database is started.
5. A query is issued against the MYOBJ_CTRL table that has a predicate OBJECT_ID=1500.
1. The Exadata cell services software conducts I/O requests on I MO storage regions.
7. MYOBJ_STATE’S region index is populated with high and low values for the OBJECT_ID column during the I/O request.
6. A subsequent query is Issued against the MYOBJ_CTRL table that has a predicate OBJECT_ID=2234.
2. cellsrv checks the high and low values, and determines the storage region does not contain any values meeting the predicate.
4. Physical I/O to the region is bypassed if the query selection falls outside the high/low storage index storage.
Note: Example:
Step 1 (step 5 in answer): The first time that each cell’s cell services software issued an I/O request to access extents from the D14.MYOBJ_UNCOMP table, Exadata populated a region index for each storage index with the high and low values found for the OBJECT_ID column, based on the WHERE OBJECT_ID BETWEEN 100 AND 200 query predicate.
Step 2 (step 6 in answer) : Subsequent queries against this table generated an iDB message instructing Exadata’s cell services software to read the same sets of extents as the first query, but in this case the region indexes would have been populated based on the I/Os read from the first query.
Step 3: (step 2 in answer) Prior to issuing a physical disk read, cellsrv checks the high and low values stored in the region index and if it determines that a storage region does not contain any values meeting the query predicate, bypasses the physical I/O to the region.
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