Workflow Variable Size Management#

Dify enforces two complementary size controls on workflow variables: a hard creation-time limit that rejects oversized variables during variable construction, and a runtime truncation system that structure-preservingly shrinks variables before they are stored or streamed to clients.

Two Distinct Size Controls#

1. MAX_VARIABLE_SIZE — Creation-time hard limit#

MAX_VARIABLE_SIZE (default 200 KB, set in WorkflowConfig) is checked in variable_factory._build_variable_from_mapping(). If a newly constructed variable's .size exceeds the limit, a VariableError is raised immediately. This prevents oversized variables from ever entering the workflow graph.

# api/configs/feature/__init__.py — WorkflowConfig
MAX_VARIABLE_SIZE: PositiveInt = Field(default=200 * 1024, ...) # 200 KiB

2. WORKFLOW_VARIABLE_TRUNCATION_* — Runtime truncation limits#

A separate config class WorkflowVariableTruncationConfig controls the runtime truncation pipeline:

All three values are loaded from environment variables and feed the VariableTruncator.default() factory method.

VariableTruncator — Structure-preserving truncation#

api/services/variable_truncator.py implements the core truncation logic. The main class, VariableTruncator, supports two entry points:

• truncate(segment) — Truncates a single Segment. Strings are capped at _string_length_limit; arrays and objects are recursively trimmed to fit _max_size_bytes. If the result still exceeds the max, the value is serialized to a JSON string and hard-truncated as a last resort.
• truncate_variable_mapping(v) — Truncates a key-value mapping (e.g., inputs, process_data, outputs of a WorkflowNodeExecution record) by distributing the remaining byte budget across entries proportionally.

Size accounting avoids repeated JSON serialization via calculate_json_size(), which recursively estimates the serialized JSON byte count from the in-memory value.

Per-type truncation strategies#

Object truncation keeps all keys when possible, dropping from the end only when the budget is exhausted. The maximum recursion depth is capped at 100 to prevent stack overflow.

DummyVariableTruncator — Service API no-op#

DummyVariableTruncator implements BaseTruncator but passes all values through unchanged. It is injected in WorkflowResponseConverter.__init__() when invoke_from == InvokeFrom.SERVICE_API, preserving backward-compatible full-fidelity responses for Service API callers.

Call Sites#

Key files#

• api/services/variable_truncator.py — VariableTruncator, DummyVariableTruncator, BaseTruncator
• api/configs/feature/__init__.py — WorkflowConfig.MAX_VARIABLE_SIZE, WorkflowVariableTruncationConfig
• api/factories/variable_factory.py — Creation-time size check at line 118–119
• api/core/app/apps/common/workflow_response_converter.py — Truncator selection (real vs. no-op)