1Z0-052 · Question #27
What can you achieve by implementing reverse key index?
The correct answer is C. Prevent contention on the highest leaf block when using sequences to generate keys. A reverse key index reverses the byte order of each indexed column value, distributing sequential inserts (such as those from a sequence) across multiple leaf blocks to eliminate hot-block contention.
Question
What can you achieve by implementing reverse key index?
Options
- AReverse the bytes of each column indexed including the row ID
- BStore a bitmap for each key value instead of a list of row IDs in the leaf node
- CPrevent contention on the highest leaf block when using sequences to generate keys
- DRemove repeated key values from the index to fit more index entries in a given amount of disk space
How the community answered
(21 responses)- A10% (2)
- C86% (18)
- D5% (1)
Why each option
A reverse key index reverses the byte order of each indexed column value, distributing sequential inserts (such as those from a sequence) across multiple leaf blocks to eliminate hot-block contention.
A reverse key index reverses the bytes of the indexed column values only; the row ID (ROWID) is stored as-is and is not reversed.
Storing a bitmap per key value instead of a list of row IDs describes a bitmap index, not a reverse key index.
When a sequence generates monotonically increasing key values, all new index entries cluster at the rightmost leaf block, creating a hot block under concurrent inserts. A reverse key index reverses the bytes of each column value before storing it, spreading the entries across many different leaf blocks and eliminating this contention - though it makes range scans unsupported.
Suppressing repeated key values to save space describes index key compression (the COMPRESS keyword), not a reverse key index.
Concept tested: Oracle reverse key index contention prevention
Source: https://docs.oracle.com/en/database/oracle/oracle-database/19/admin/managing-indexes.html
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