synchronize_seqscans

synchronize_seqscans — Enables synchronized sequential scans. Observed in PG9.0–19 Beta 3; its last measured boot default is on 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: “Enables synchronized sequential scans.”

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 / Previous PostgreSQL Versions: Upstream classification
Latest boot value , Valueon: on

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	`on`	—	on

How it works

Enables synchronized sequential scans. It can be changed at session scope, so different sessions may observe different behavior.

Concurrent sequential scans of the same large relation may join a shared scan position, improving cache reuse while returning rows in a less predictable physical order. SQL without ORDER BY has no ordering guarantee regardless of this switch.

Monitor and change synchronize_seqscans together with default_with_oids, lo_compat_privileges, operator_precedence_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	Normally keep it on so concurrent large-table scans can share cache footprint. Queries that require deterministic order must use ORDER BY; disabling this setting is not an ordering contract.
OLAP	Analytical concurrency is the most likely beneficiary. Experiment at session scope only when repeatable benchmarks show the shared scan position harms locality.
Small nodes	Keep the default. When data fits in cache or concurrent scans are rare, this setting usually needs no attention and is not a bottleneck.

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.

default_with_oids · lo_compat_privileges · operator_precedence_warning · standard_conforming_strings · array_nulls · backslash_quote