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bug: LANGFUSE_MAX_EVENT_SIZE_BYTES is parsed but never enforced for score events

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Seit 09.10.2026.

  • #1970 von @moneebullah25 — offen

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Beschreibung

bug feat-scores sdk-python
Describe the bug

MAX_EVENT_SIZE_BYTES = int(os.environ.get("LANGFUSE_MAX_EVENT_SIZE_BYTES", 1_000_000)) (score_ingestion_consumer.py#L18) is not referenced anywhere else in the repo (grep -rn MAX_EVENT_SIZE langfuse only finds the definition). The env var was added in #1103 ("make max event and batch size configurable"), but it currently has no effect: an oversized score event is posted as-is instead of being dropped or truncated.

Secondary point: in _next() the running total is compared to MAX_BATCH_SIZE_BYTES only after the event has already been appended (score_ingestion_consumer.py#L83-L108), so a batch can exceed the batch limit by up to one event (and since single events are not capped, by an arbitrary amount).

Expected: events above LANGFUSE_MAX_EVENT_SIZE_BYTES are dropped (with a logged error) or truncated, and the batch limit is checked before appending.

Actual: a 10 MB score comment is sent in a single request. Whether the server then rejects it and how that is surfaced depends on the 4xx handling; today a rejected batch is dropped without a log line (see #1874, which is about that part). Users who set the env var, as in langfuse/langfuse#7027, get no client-side effect from it.

Severity is low to medium: it only affects unusually large score payloads, but the env var suggests protection that is not there.

Steps to reproduce
import httpx
from queue import Queue
from langfuse._utils.request import LangfuseClient
from langfuse._task_manager.score_ingestion_consumer import ScoreIngestionConsumer, MAX_EVENT_SIZE_BYTES, MAX_BATCH_SIZE_BYTES
sizes = []
def h(req): sizes.append(len(req.content)); return httpx.Response(200, json={})
cl = LangfuseClient("pk", "sk", "http://x", "1", 5, httpx.Client(transport=httpx.MockTransport(h)))
q = Queue(); c = ScoreIngestionConsumer(ingestion_queue=q, identifier=0, client=cl, public_key="pk", flush_at=15)
q.put({"id": "big", "type": "score-create", "body": {"comment": "x" * 10_000_000}})
c.upload()
print("MAX_EVENT", MAX_EVENT_SIZE_BYTES, "MAX_BATCH", MAX_BATCH_SIZE_BYTES, "posted bytes", sizes)

Observed output:

MAX_EVENT 1000000 MAX_BATCH 2500000 posted bytes [10000173]
Langfuse Cloud or self-hosted?

Either; the behaviour is client side only.

If self-hosted, what version are you running?

n/a

SDK and integration versions

langfuse 4.17.0 (main @ bf11ec121479145923ff27b32ec2ad1d06fd2d51), Python 3.14.0.

Additional information

Possible direction: after computing item_size in _next(), if item_size > MAX_EVENT_SIZE_BYTES: logger.error(...); self._ingestion_queue.task_done(); continue, and check total_size + item_size > MAX_BATCH_SIZE_BYTES before appending, carrying the event into the next batch. Alternatively remove the constant and the env var if client-side enforcement is not wanted.

Minor and separate: int(os.environ[...]) at import time makes import langfuse raise on a malformed value (this was also noted in the review of #1103).

Related: #1874 (4xx batch drops are not logged), langfuse/langfuse#7027 (413 from the server with LANGFUSE_MAX_EVENT_SIZE_BYTES set).

Are you interested in contributing a fix for this bug?

Yes

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