Init parameterOptimizer & SQL

OPTIMIZER_MODE

What it controls

Whether the optimizer aims for total throughput or fast first rows.

Know this before you change it

Leave it at ALL_ROWS and use FIRST_ROWS(n) hints where needed.

Default: ALL_ROWS

Check and change it

1-- Current value on every instance2SELECT inst_id, name, value, isdefault, ismodified3FROM gv$parameter4WHERE name = 'optimizer_mode';5 6-- Value stored in the spfile7SELECT sid, value FROM v$spparameter WHERE name = 'optimizer_mode' AND isspecified = 'TRUE';8 9-- Dynamic: takes effect now and is kept after a restart10ALTER SYSTEM SET optimizer_mode = ALL_ROWS SCOPE = BOTH SID = '*';11 12-- Or for your own session only13ALTER SESSION SET optimizer_mode = ALL_ROWS;14 15-- Remove it from the spfile to go back to the default at the next restart16ALTER SYSTEM RESET optimizer_mode SCOPE = SPFILE SID = '*';

Open in the parameter referenceOracle's reference

More in Optimizer & SQL

• OPTIMIZER_FEATURES_ENABLEMakes the optimizer behave like an earlier release.
• OPTIMIZER_ADAPTIVE_STATISTICSAdaptive statistics features such as SQL plan directives and dynamic statistics (12.2 and later).
• OPTIMIZER_ADAPTIVE_PLANSLets the optimizer switch join methods during the first execution (12.2 and later).
• CURSOR_SHARINGWhether Oracle replaces literals with bind variables before parsing.
• STATISTICS_LEVELHow much performance data Oracle collects.
• DB_FILE_MULTIBLOCK_READ_COUNTBlocks read in one I/O during full scans.
• PARALLEL_MAX_SERVERSThe most parallel execution processes per instance.
• PARALLEL_DEGREE_POLICYWhether Oracle chooses the degree of parallelism itself.
• RESULT_CACHE_MAX_SIZEMemory for the server result cache.