prestodb/presto · error · PrestoException

GENERIC_USER_ERROR

GENERIC_USER_ERROR

Error message

Remote functions are not enabled

What it means

Remote (server-side external) functions are gated behind a session/config flag. PlanRemoteProjections detects remote-function calls in a projection; if any exist but the remote-functions feature is disabled, it throws GENERIC_USER_ERROR telling the user to enable the feature.

Source

Thrown at presto-main-base/src/main/java/com/facebook/presto/sql/planner/iterative/rule/PlanRemoteProjections.java:95

    public Pattern<ProjectNode> getPattern()
    {
        return PATTERN;
    }

    @Override
    public Result apply(ProjectNode node, Captures captures, Rule.Context context)
    {
        if (!node.getLocality().equals(UNKNOWN)) {
            // Already planned
            return Result.empty();
        }
        // Fast check for remote functions
        if (node.getAssignments().getExpressions().stream().noneMatch(expression -> expression.accept(new ExternalCallExpressionChecker(functionAndTypeManager), null))) {
            // No remote function
            return Result.ofPlanNode(new ProjectNode(node.getSourceLocation(), node.getId(), node.getSource(), node.getAssignments(), LOCAL));
        }
        if (!isRemoteFunctionsEnabled(context.getSession())) {
            throw new PrestoException(GENERIC_USER_ERROR, "Remote functions are not enabled");
        }
        List<ProjectionContext> projectionContexts = planRemoteAssignments(node.getAssignments(), context.getVariableAllocator());
        checkState(!projectionContexts.isEmpty(), "Expect non-empty projectionContexts");
        PlanNode rewritten = node.getSource();
        for (ProjectionContext projectionContext : projectionContexts) {
            rewritten = new ProjectNode(node.getSourceLocation(), context.getIdAllocator().getNextId(), rewritten, Assignments.builder().putAll(projectionContext.getProjections()).build(), projectionContext.remote ? REMOTE : LOCAL);
        }
        return Result.ofPlanNode(rewritten);
    }

    @VisibleForTesting
    public List<ProjectionContext> planRemoteAssignments(Assignments assignments, VariableAllocator variableAllocator)
    {
        ImmutableList.Builder<List<ProjectionContext>> assignmentProjections = ImmutableList.builder();
        for (Map.Entry<VariableReferenceExpression, RowExpression> entry : assignments.getMap().entrySet()) {
            List<ProjectionContext> rewritten = entry.getValue().accept(new Visitor(functionAndTypeManager, variableAllocator), null);
            if (rewritten.isEmpty()) {
                assignmentProjections.add(ImmutableList.of(new ProjectionContext(ImmutableMap.of(entry.getKey(), entry.getValue()), false)));

View on GitHub (pinned to 55bb57d202)

Solutions

1. Enable it: SET SESSION remote_functions_enabled = true
2. Set remote-functions-enabled=true in the coordinator config.properties
3. Remove or replace the remote function with a local UDF if the feature cannot be enabled

Example fix

// before
SELECT remote_model_classify(text) FROM messages; -- flag off
// after
SET SESSION remote_functions_enabled = true;
SELECT remote_model_classify(text) FROM messages;

SHOW SESSION LIKE 'remote_functions_enabled';

null

try {
    return query(sql);
} catch (PrestoException e) {
    if (e.getErrorCode() == GENERIC_USER_ERROR.toErrorCode() && e.getMessage().contains("Remote functions")) {
        setSessionProperty("remote_functions_enabled", "true");
        return retryQuery(sql);
    }
    throw e;
}

When it happens

Trigger: A query projection references an external/remote function (matched by ExternalCallExpressionChecker) while 'remote-functions-enabled' is false in the session or config.

Common situations: Calling remote functions on a cluster without the flag enabled; config migrated from a cluster where remote functions were on; testing AI/remote UDFs without enabling the feature.

Related errors

• NOT_SUPPORTED
• Output column (%s) definition not found in input selections:

AI-assisted analysis of prestodb/presto@55bb57d202 (2026-09-04). Data as JSON: /api/errors/618f1a64b7b2d9bb. Report an issue: GitHub.