Foreign Scan

ForeignScan

Delegates a foreign scan or supported direct modification to the foreign-data wrapper.

Reading PostgreSQL 18.6.

Description

Delegates a foreign scan or supported direct modification to the foreign-data wrapper.

Core node tag: T_ForeignScan
Structured EXPLAIN Node Type: Foreign Scan
Inputs: Foreign-data wrapper plan and callbacks
Output: Provider-defined scan or RETURNING tuples
Executor initializer: ExecInitForeignScan
Memory mechanism: unclassified

EXPLAIN names and attributes

Structured formats use the Node Type above. Text-format spellings can also include operation, strategy, join type, scan direction or aggregation-stage attributes.

Text names recorded by this source: Foreign Scan, Foreign Insert, Foreign Update, Foreign Delete.

Parallel-aware and parallel-safe are different plan properties. A node running inside a parallel worker is not necessarily a parallel-aware node.

Memory and temporary storage

This extraction does not assign a universal memory limit or spill policy to this node. Inspect the same-build implementation and its expressions or provider.

Parallel execution and instrumentation

The source callbacks below can coordinate execution or collect worker instrumentation. Their presence is not a blanket claim that this node supports a shared parallel scan or shared state.

Callbacks in this build: ExecForeignScanEstimate, ExecForeignScanInitializeDSM, ExecForeignScanInitializeWorker, ExecForeignScanReInitializeDSM.

Executor implementation notes

nodeForeignscan.c Routines to support scans of foreign tables

ExecForeignScan scans a foreign table. ExecInitForeignScan creates and initializes state info. ExecReScanForeignScan rescans the foreign relation. ExecEndForeignScan releases any resources allocated.

direct modifications cannot be re-evaluated, so shouldn't get here during EvalPlanQual processing

Insert valid value into tableoid, the only actually-useful system column.

ForeignRecheck -- access method routine to recheck a tuple in EvalPlanQual

EXPLAIN identity in core source

case T_ForeignScan:
			sname = "Foreign Scan";
			switch (((ForeignScan *) plan)->operation)
			{
				case CMD_SELECT:
					pname = "Foreign Scan";
					operation = "Select";
					break;
				case CMD_INSERT:
					pname = "Foreign Insert";
					operation = "Insert";
					break;
				case CMD_UPDATE:
					pname = "Foreign Update";
					operation = "Update";
					break;
				case CMD_DELETE:
					pname = "Foreign Delete";
					operation = "Delete";
					break;
				default:
					pname = "???";
					break;
			}
			break;

EXPLAIN labels in this source build

Text-format label	Structured node identity
Foreign Scan	Foreign Scan
Foreign Insert	Foreign Scan
Foreign Update	Foreign Scan
Foreign Delete	Foreign Scan

Related entries

Documentation and source

Source build

Version: 18.6
Build: PostgreSQL 18.6 source archive
Source fingerprint: 555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f

Compare versions

PostgreSQL 17 → 18: unchanged.

Compares recorded interfaces and attributes. Source fingerprints and build metadata are excluded; an absent sample is not proof of the introduction or removal release.

Related entries

Custom ScanCustomScan

Export JSON · Back to Plan Nodes · Recorded in PostgreSQL 10 through 20; the first sample is not necessarily its introduction.