URGENT: Delta writes to S3 fail after workspace migrated to Premium

DBU100725 — Tue, 07 Oct 2025 13:27:05 GMT

Delta writes to S3 fail after workspace migrated to Premium (401 “Credential was not sent or unsupported type”)

Summary

After our Databricks workspace migrated from Standard to Premium, all Delta writes to S3 started failing with:

com.databricks.s3commit.DeltaCommitRejectException: ... 401: Credential was not sent or was of an unsupported type for this API.

The same code ran for years on Standard. Reads from Delta work, and read/write as CSV/Parquet/TXT still work. The failure occurs only during the Delta commit phase.

Environment

Cloud: AWS
Workspace tier: Premium (recently migrated from Standard)
Compute: classic (non-serverless) all-purpose/job clusters
Auth to S3: static S3A keys set in notebook at runtime
Buckets involved: s3://<bucket-name>/... (Delta target), s3://<bucket-name>/... (staging)
We also have an IAM Role (cluster role) with S3 permissions (see “IAM details”)

Exact error (top of stack)

DeltaCommitRejectException: rejected by server 26 times, most recent error: 401: Credential was not sent or was of an unsupported type for this API.

    at com.databricks.s3commit.DeltaCommitClient.commitWithRetry...

    at com.databricks.tahoe.store.EnhancedS3AFileSystem.putIfAbsent...

    ...

Minimal repro

from pyspark.sql.functions import lit

# Static keys (legacy)
sc._jsc.hadoopConfiguration().set('fs.s3a.awsAccessKeyId',   config['AWS_ACCESS_KEY'])
sc._jsc.hadoopConfiguration().set('fs.s3a.awsSecretAccessKey', config['AWS_SECRET_KEY'])

# (no session token)

# Simple delta write
(spark.range(1).withColumn("date", lit("1970-01-01"))
 .write.format("delta")
 .mode("overwrite").partitionBy("date")
 .save("s3://<bucket-name>/path/ops/_tmp_delta_write_check"))

# Result: fails with 401 during Delta commit

Control tests

- spark.read.format("delta").load("s3://<bucket-name>/path/...") → works
- .write.mode("overwrite").parquet("s3a://<bucket-name>/path/staging/...") → works
- .write.csv(...) / .write.text(...) → work

What changed

Only the workspace tier (Standard → Premium). Code, buckets, and IAM remained the same.

IAM details (high level)

- Cluster role has S3 permissions (Get/Put/Delete on object prefixes; ListBucket on buckets).

- CSV/Parquet I/O proves general S3 access is OK.

- Happy to share a redacted IAM policy if needed.

Spark/cluster config (relevant bits)

- We set static keys in the first cell via fs.s3a.awsAccessKeyId/SecretAccessKey.

- We have seth the IAM Cluster/Instance profile for the workspace

Re: URGENT: Delta writes to S3 fail after workspace migrated to Premium

DBU100725 — Tue, 07 Oct 2025 15:05:41 GMT

The update/append to delta on s3 fails with both Databrciks Runtime 13.3 and 15.4.

Re: URGENT: Delta writes to S3 fail after workspace migrated to Premium

dkushari — Tue, 21 Oct 2025 18:52:47 GMT

Hi @DBU100725 - Are you using a No isolation shared cluster? Can you check if this was turned ON in your account?

topic URGENT: Delta writes to S3 fail after workspace migrated to Premium in Data Engineering

URGENT: Delta writes to S3 fail after workspace migrated to Premium

Delta writes to S3 fail after workspace migrated to Premium (401 “Credential was not sent or unsupported type”)

Summary

Environment

Exact error (top of stack)

Minimal repro

Control tests

What changed

IAM details (high level)

Spark/cluster config (relevant bits)

Re: URGENT: Delta writes to S3 fail after workspace migrated to Premium

Re: URGENT: Delta writes to S3 fail after workspace migrated to Premium