Function Scan

Description

Scans table-function results from a FROM clause.

Core node tag

T_FunctionScan

Structured EXPLAIN Node Type

Function Scan

Inputs

One or more table functions

Output

Function result tuples

Executor initializer

ExecInitFunctionScan

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: Function Scan.

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: none extracted from this node implementation.

Executor implementation notes

nodeFunctionscan.c Support routines for scanning RangeFunctions (functions in rangetable).

Fast path for the trivial case: the function return type and scan result type are the same, so we fetch the function result straight into the scan result slot. No need to update ordinality or rowcounts either.

If first time through, read all tuples from function and put them in a tuplestore. Subsequent calls just fetch tuples from tuplestore.

paranoia - cope if the function, which may have constructed the tuplestore itself, didn't leave it pointing at the start. This call is fast, so the overhead shouldn't be an issue.

Increment or decrement ordinal counter before checking for end-of-data, so that we can move off either end of the result by 1 (and no more than 1) without losing correct count. See PortalRunSelect for why we can assume that we won't be called repeatedly in the end-of-data state.

EXPLAIN identity in core source

case T_FunctionScan:
			pname = sname = "Function Scan";
			break;

Related entries

• EXPLAIN
• Using EXPLAIN
• Parallel plans

Documentation and source

• src/backend/commands/explain.c:1465
• src/backend/executor/execProcnode.c:254
• src/backend/executor/nodeFunctionscan.c
• src/include/nodes/plannodes.h

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

• Bitmap Heap ScanBitmapHeapScan
• CTE ScanCteScan
• Index Only ScanIndexOnlyScan
• Index ScanIndexScan
• Named Tuplestore ScanNamedTuplestoreScan
• Sample ScanSampleScan
• Seq ScanSeqScan
• Subquery ScanSubqueryScan
• Table Function ScanTableFuncScan
• Tid Range ScanTidRangeScan
• Tid ScanTidScan
• Values ScanValuesScan