max_index_keys

Definition PG 18 manual

Reports the maximum number of index keys. It is determined by the value of INDEX_MAX_KEYS when building the server. The default value is 32 keys.

How it works

Shows the maximum number of index keys. It is read-only and cannot be changed with SET or configuration-file edits.

It exposes the INDEX_MAX_KEYS build limit on index attributes, including key and INCLUDE columns where applicable.

Interpret it with max_function_args, max_identifier_length, block_size. Applications and operations tooling may read max_index_keys for capability or environment detection, but cannot SET it; cross-cluster comparisons must account for build, initdb, and current-database differences.

Operational considerations

Trying to change read-only max_index_keys with SET or a configuration file.

Assuming every cluster, database, or vendor build reports the same value.

Ignoring the value in file-format or feature-compatibility checks.

Treating reported metadata as a performance target instead of an environment fact.

Workload guidance

OLAP: Not tunable. Use max_index_keys to verify format, build, or resource assumptions on analytical nodes and keep every read/write candidate compatible.

OLTP: Not tunable. Record max_index_keys as a deployment/capability fact; if it is unexpected, fix the binary, initdb, or database-creation process rather than trying SET.

SMALL: Not tunable. Preserve it in inventory and incident reports; do not custom-build or rebuild merely to change it without a demonstrated compatibility need.