MySQL skipped range optimization because its internal range optimizer exceeded memory or slot capacity.
ER_CAPACITY_EXCEEDED_IN_RANGE_OPTIMIZER means MySQL skipped range optimization after exhausting internal memory or range slots. Trim OR conditions, add supporting indexes, or raise range_optimizer_max_mem_size to restore optimized execution.
ER_CAPACITY_EXCEEDED_IN_RANGE_OPTIMIZER
Error 3171 appears when MySQL's range optimizer cannot allocate enough internal structures to evaluate all range conditions in the query.
Instead of producing efficient range scans, the optimizer falls back to less selective access paths, which can slow queries dramatically.
The range optimizer tracks every disjunctive range it must evaluate. Excessive OR predicates, IN lists, or complex BETWEEN ranges can overflow its capacity.
Low values for range_optimizer_max_mem_size or limited RAM can trigger the condition even for moderate queries.
First, simplify the WHERE clause by breaking large IN lists into temporary tables or replacing OR chains with UNION ALL.
If query rewrite is impossible, increase the session or global range_optimizer_max_mem_size to let MySQL allocate more memory for range analysis.
Reports that filter on hundreds of dynamic IDs via IN (…) often hit the limit; moving the ID list into a temp table and joining restores range scans.
ETL jobs with generated OR predicates benefit from splitting the workload and processing smaller ID batches.
Create composite indexes that cover the most selective columns so the optimizer needs fewer ranges.
Monitor queries with EXPLAIN; if you see full table scans where range scans are expected, inspect predicate complexity before the error surfaces.
ER_TOO_MANY_SELECTS signals excessive UNION depth and can co-occur with range capacity issues. Normalize the query structure to resolve both.
Hundreds of column = value conditions exceed the internal range slot limit.
Dynamic code that injects thousands of IDs into an IN clause pushes memory usage past range_optimizer_max_mem_size.
Default memory cap is too small for analytical workloads in older MySQL versions.
Without proper indexes, the optimizer must build more ranges to evaluate filters, increasing memory pressure.
Indicates that the optimizer pruned access paths due to complexity limits.
Triggers when the estimated joined rows exceed max_join_size. Both errors point to oversized queries.
Fires when a UNION contains too many SELECT statements, similar to range overflow.
Shows that a range condition is not cacheable, often arising in complex predicates.
Yes, but increase it gradually and monitor RAM usage to avoid server-wide memory pressure.
The query still returns correct results; only performance degrades because MySQL cannot use range access.
ER_CAPACITY_EXCEEDED_IN_RANGE_OPTIMIZER was introduced in MySQL 5.7.9 and exists in all later versions, including 8.0.
Galaxy's AI copilot can rewrite large OR predicates into UNION ALL or temp-table joins automatically, reducing the risk before queries hit production.
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