FIXED TABLE FIXED INDEX
FIXED TABLE (FIXED INDEX) shows indexed access to one of the internal dynamic performance views known as X$ tables
Detailed Description​
FIXED TABLE (FIXED INDEX) shows indexed access to one of the dynamic performance tables known as X$ tables. These are in-memory structures rather than normal SQL tables and are maintained by the Oracle server. Direct access to the X$ tables is strongly advised against. They will however, show up in explain plans. Their contents are usually exposed through the V$... and GV$... set of views.
Performance of these objects can suffer if the optimizer is not aware of the actual statistics for them, on versions older than 12c use the DBMS_STATS.GATHER_FIXED_OBJECTS_STATS procedure to update them.
Although newer versions include fixed tables in the scheduled statistics jobs, it is recommended by Oracle that fixed object statistics are gathered whilst a representative workload is being run.
Additional Links​
- Oracle Tuning Guide - Gathering Statistics for Fixed Objects
- Oracle Magazine - How to read an execution plan
- Oracle Tuning Guide - Explaining and Displaying Execution Plans
- Oracle Tuning Guide - Comparing Execution Plans Tutorial
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