Query is Slow, Explain Plan Shows "MERGE JOIN CARTESIAN" Operation Which is Taking Most of the Time
(Doc ID 2032840.1)
Last updated on DECEMBER 14, 2020
Applies to:Oracle Database - Enterprise Edition - Version 10.2.0.5 and later
Oracle Database Cloud Schema Service - Version N/A and later
Oracle Database Exadata Cloud Machine - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Oracle Database Exadata Express Cloud Service - Version N/A and later
Information in this document applies to any platform.
- Query performs slowly: this can manifest in a number of different ways dependent on the environment and the amount of data involved (e.g. high memory and temporary table usage, high CPU etc. )
- Execution plan shows that a MERGE JOIN CARTESIAN operation is involved:
- All the objects in the query are joined to one of the other objects - there are no missing joins
- The MERGE JOIN CARTESIAN operation is taking most of the time in the query or sparks off slow activity in the following steps.
- The row counts for the MERGE JOIN CARTESIAN operation bear no relationship with reality. For example, the E-Rows for the MERGE JOIN CARTESIAN operation are inaccurate compared to the real number of rows that these steps involve.
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