shared_memory_size_in_huge_pages

Definition PG 18 manual

Reports the number of huge pages that are needed for the main shared memory area based on the specified huge_page_size. If huge pages are not supported, this will be -1.

This setting is supported only on Linux. It is always set to -1 on other platforms. For more details about using huge pages on Linux, see Section 18.4.5.

How it works

Shows the number of huge pages needed for the main shared memory area. It is read-only and cannot be changed with SET or configuration-file edits.

It estimates how many huge pages the main shared-memory segment needs and returns -1 when the platform cannot provide the estimate.

Interpret it with shared_memory_size, huge_pages, huge_pages_status. Applications and operations tooling may read shared_memory_size_in_huge_pages 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 shared_memory_size_in_huge_pages 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 shared_memory_size_in_huge_pages to verify format, build, or resource assumptions on analytical nodes and keep every read/write candidate compatible.

OLTP: Not tunable. Record shared_memory_size_in_huge_pages 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.