PostgreSQL raises 39P02 when a set-returning function violates the internal execution protocol, usually due to faulty C extensions or mis-declared SQL functions.
PostgreSQL Error 39P02 – srf_protocol_violated appears when a set-returning function breaks the engine’s call/return contract. The fault almost always lives in a custom C or SQL function. Recompile or rewrite the function to obey the SRF API, then retry the query.
PostgreSQL Error 39P02
PostgreSQL throws error code 39P02 with the condition name srf_protocol_violated when a set-returning function (SRF) does not follow the execution protocol expected by the PostgreSQL executor.
The engine expects every SRF to report its state with SRF_RETURN_NEXT and SRF_RETURN_DONE in a strict sequence.
If a function returns tuples after signaling it is finished, or forgets to report completion, PostgreSQL halts the query and emits 39P02.
The error commonly surfaces while calling user-defined functions written in C, PL/pgSQL, or SQL that were declared RETURNS SETOF.
Extension code compiled for an older PostgreSQL version is a frequent trigger.
Production sightings often involve table-valued functions used in FROM clauses, lateral joins, or nested inside JSON processing pipelines.
An SRF returns SRF_RETURN_NEXT after it already returned SRF_RETURN_DONE.
A function fails to return SRF_RETURN_DONE at all, causing the executor to detect an infinite stream.
ABI mismatch between the PostgreSQL server version and the compiled extension code breaks the call conventions.
Incorrect SQL wrapper declares RETURNS SETOF while the underlying C function returns a scalar type.
Locate the exact function named in the server log.
Review its C or PL/pgSQL source for correct SRF protocol usage.
For C functions, ensure the callback returns SRF_RETURN_DONE once, and does not enter again.
Recompile against the server’s pg_config headers.
If the function is pure SQL, remove the SETOF modifier or rewrite using RETURNS TABLE with a proper RETURN NEXT/RETURN QUERY pattern.
Old PostGIS or TimescaleDB binaries on a new PostgreSQL major release: upgrade the extension packages and run ALTER EXTENSION UPDATE.
Hand-written C SRF: add a has_done flag in the FuncCallContext and guard subsequent calls.
PL/pgSQL function with misplaced RETURN NEXT after RETURN: reorder the statements so RETURN NEXT appears before the final RETURN.
Recompile all C extensions whenever PostgreSQL is upgraded to a new major version.
Use regression tests that call each SRF in set-returning and scalar contexts to catch protocol issues early.
Prefer SQL or PL/pgSQL functions unless C speed is critical; higher-level languages handle protocol details automatically.
42883 undefined_function - Raised when a called function name is not found.
Verify function existence and signature.
42703 undefined_column - Appears when an SRF references a column that does not exist in the calling query.
XX000 internal_error - Generic internal failure that may mask SRF misuse; check server logs for 39P02 hints.
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Almost always. Core PostgreSQL rarely triggers it by itself. The culprit is usually a custom or third-party function.
Yes, if RETURN NEXT and RETURN statements are mis-ordered or missing. The language’s runtime enforces the same SRF protocol.
Not necessarily. After any major upgrade, recompile or upgrade all extensions to versions built for the new server ABI.
Galaxy’s AI copilot surfaces function definitions instantly, flags outdated binaries, and lets teams endorse the corrected version, preventing future protocol violations.
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