High Number of Child Cursors for Queries using due to HASH_MATCH_FAILED
(Doc ID 2210515.1)
Last updated on APRIL 09, 2021
Applies to:Oracle Database - Enterprise Edition - Version 188.8.131.52 and later
Oracle Database Cloud Schema Service - Version N/A and later
Gen 1 Exadata Cloud at Customer (Oracle Exadata Database Cloud Machine) - Version N/A and later
Oracle Database Exadata Express Cloud Service - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Information in this document applies to any platform.
- High version counts for many queries with HASH_MATCH_FAILED:
By definition, HASH_MATCH_FAILED means that no existing child cursors have the unsafe literal bind hash values required by the current cursor.
In such cases the query executed contains TIMESTAMP column. The TIMESTAMP column is marked as a none data literals so we are generating different hash for each none data literals each time function "Search Child List" is called and that's why the different child is created due to hash-mismatch(HASH_MATCH_FAILED=YES).
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