transform_null_equals

transform_null_equals — Treats “expr=NULL” as “expr IS NULL”. Observed in PG9.0–19 Beta 3; its last measured boot default is off in PG19 Beta 3, with user context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA.

Note

Fact — official short description: “Treats “expr=NULL” as “expr IS NULL”.”

Identity

Type , Valuebool: Upstream pg_settings type
Context , Valueuser: Settable by an ordinary user
Unit , Value—: Raw unit
Range , Value—: Raw limits in the last observed version
Enum values , Value—: — for non-enum types
Category , ValueVersion and Platform Compatibility / Other Platforms and Clients: Upstream classification
Latest boot value , Valueoff: off

Lifecycle

Fact	Value
First observed	PG9.0 (research boundary)
Present in	PG9.0–19 Beta 3
Removed in	No
Introduction commit	Not asserted: predates the PG9.0 research boundary
Commit date	—
Discussion	—

Default history

Measured PG9.0–19 Beta 3 boot defaults
Versions	Raw `boot_val`	Unit	Human value
PG9.0–19 Beta 3	`off`	—	off

How it works

Treats “expr=NULL” as “expr IS NULL”. It can be changed at session scope, so different sessions may observe different behavior.

The parser rewrites expr = NULL to expr IS NULL for broken legacy clients. SQL’s normal three-valued semantics make equality with NULL yield unknown, so enabling this can hide application defects and does not rewrite other NULL comparisons.

Monitor and change transform_null_equals together with array_nulls, backslash_quote, escape_string_warning. Validate on the relevant server role and real workload, then use its user context to choose session change, reload, or restart; a historical boot default is not the current effective value.

Tuning advice

Tip

Advice. These are workload-specific starting points and must be validated with measurements.

Workload	Guidance
OLTP	Keep the modern default and repair legacy clients/SQL that depend on transform_null_equals. Test migration at session scope first; do not make a compatibility switch permanent cluster policy.
OLAP	Regression-test ETL, generated SQL, and old drivers, where parsing/quoting assumptions hide. Performance is rarely a reason to change this switch.
Small nodes	Keep the default without a legacy requirement. If temporarily enabled, record owner, affected connections, and a removal date.

Pigsty

Values use the fixed 8-vCPU, 32-GiB, 100-GiB SSD fixture and render the current Pigsty templates for PG19 Beta 3; this does not assert current Pigsty support for that historical or beta release.

Template	Effective value	Versus upstream boot	Source expression
OLTP	Unmodified	—	—
OLAP	Unmodified	—	—
CRIT	Unmodified	—	—
TINY	Unmodified	—	—

Caution

Advice — pending human review. Fact from the current Pigsty template projection: OLTP: PG9.0–19 Beta 3 unmodified; OLAP: PG9.0–19 Beta 3 unmodified; CRIT: PG9.0–19 Beta 3 unmodified; TINY: PG9.0–19 Beta 3 unmodified. No Pigsty-specific rationale is inferred from an absent override.

Common pitfalls

Keeping a compatibility switch permanently instead of fixing the client.
Testing in one session and deploying globally to unrelated applications.
Confusing parsing compatibility with data or security compatibility.
Forgetting to remove an override after the upgrade migration is complete.

array_nulls · backslash_quote · escape_string_warning · standard_conforming_strings · quote_all_identifiers · allow_alter_system