enq: TX - index contention
Enqueue wait. Index transaction.
Additional Information
An enqueue is a wait for a resource held by another.
enq: TX - index contention is typically seen when splitting index blocks.
Jonathan Lewis says “If your transaction is updating columns which appear in indexes then it will be deleting and re-inserting index entries, and either action could require a leaf block split to take place. Under certain circumstances the split can take a "long" time and other sessions that want to insert into the splitting leaf block will report this enqueue wait.”
How to reduce this wait
Look for inserts or updates of an indexed column based on a increasing sequence. This activity causes index blocks to be split. Consider a reverse index to reduce the impact.
Additional Links
Oracle Docs - Oracle Enqueue Names
Oracle Community - what causes enq: TX - index contention?
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