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Freedom251 › Blog › Apache Iceberg

One Iceberg MCP Server, Seven Catalogs: What It Takes to Reach Each One

By Freedom251 Team · · 3 min read

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One Python MCP server can reach multiple Apache Iceberg REST catalogs, but the shared server code is only part of the setup. Each catalog has its own endpoint and authentication path, and reading table files may also require storage credentials and Python adapters. In a September 2026 test, author xbill exercised six catalog environments; Databricks Unity Catalog was listed but not tested. The author’s report describes a bounded test, not a compatibility guarantee for every deployment.

What the Iceberg MCP server does

The project exposes four read-only tools: iceberg_list_tables lists tables, iceberg_describe_table returns table details, iceberg_count_rows reports a count, and iceberg_scan_table reads sample data and reports scan results. Configuration selects the catalog while the server implementation is reused. The code and test assets are available in the project repository.

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This is one author-built project. Its behavior should not be taken to mean every MCP server or every Iceberg catalog uses the same settings.

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Which catalog paths were exercised?

The report names seven catalog paths. Six were exercised: local Apache Polaris plus managed Google BigLake, Microsoft OneLake, AWS Glue, Amazon S3 Tables, and Snowflake Horizon. Databricks Unity Catalog was not run because the author’s trial account had ended.

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Catalog Reported authentication and configuration Scan and storage details Test status
Apache Polaris OAuth 2.0 client ID and secret Local file storage in the described setup Tested locally; catalog version 1.7.0
Google BigLake gcloud login/token and a project header in the described setup gs:// file access Tested
Microsoft OneLake Azure CLI login adlfs adapter and abfss:// access Tested
AWS Glue AWS login with SigV4; botocore[crt] was noted for this login path s3:// access Tested in us-east-1
Amazon S3 Tables AWS login with SigV4 s3fs and botocore[crt]; catalog-issued storage credentials Tested
Snowflake Horizon Snowflake key-pair JWT Catalog-issued storage credentials described Tested
Databricks Unity Catalog No successful setup reported Not established Not run

These are configurations from the reported test, not permanent or universal vendor requirements. Check the relevant service’s current documentation before applying them to a live environment.

Why metadata access is not the same as scanning

In the reported run, listing, describing, and counting read catalog metadata and worked with PyIceberg alone. A scan goes further: it reads the table’s data files from object storage. That means a successful catalog connection does not, by itself, prove that the client has the right storage credentials or file-system adapter.

  • For the tested OneLake scan path, the report identifies adlfs and abfss:// access.
  • For the tested S3 Tables scan path, it identifies s3fs, botocore[crt], and catalog-issued storage credentials.
  • The AWS Glue setup also noted botocore[crt] for its AWS login path.
  • For BigLake, the described scan path used gs:// access.

The author observed that S3 Tables used a vended-credentials request header, while Horizon returned storage credentials without that request. Those details describe the tested configurations; they should not be assumed for all accounts or future service behavior.

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What the September 2026 test establishes—and what it does not

Author xbill reports that all four tools returned without error across the six exercised catalog environments. The sweep consisted of one run per catalog on September 18 and 19, 2026 UTC. It used iceberg_mcp.py 1.0.0, PyIceberg 0.12.0, PyArrow 25.0.1, Python 3.14.7, and the listed storage and authentication packages. The local Polaris catalog was version 1.7.0; the AWS test ran in us-east-1. Managed catalog versions were not reported.

That is evidence that this project’s four tools worked in those particular runs. It is not a repeated benchmark, a comparison of catalog speed, or a guarantee that another account, region, version, permission set, or dataset will behave the same way.

Why the reported OneLake timings should not be treated as a benchmark

The article gives conflicting timing pairs for scanning three OneLake rows: its narrative reports 858.5 seconds with DefaultAzureCredential and 3.4 seconds with AzureCliCredential, while its summary reports 553.1 seconds and 0.6 seconds, respectively. Because those figures conflict within the same report, neither pair can be treated as definitive here.

The report also provides individual call timings but says they show scale only. The catalogs used different tables and row counts, so those calls are not a like-for-like performance comparison.

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How to choose a path for your use case

  • If you only need catalog metadata: the tested project’s list, describe, and count tools used PyIceberg without reading table files. Still configure the catalog endpoint and its authentication.
  • If you need sample data or scans: plan for the object store as well as the catalog. Confirm that credentials can reach the underlying files and install the required adapter for the tested storage path.
  • If you are evaluating a catalog not exercised here: treat the project configuration as a starting point, not proof of compatibility. Unity Catalog, in particular, was not tested in this report.
  • If performance matters: run repeated tests on comparable tables in your own region and account. The report’s one-call-per-catalog observations do not support a speed ranking.

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Apache Icebergcloud storagedata catalogsMCPPyIceberg

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