timsaucer commented on code in PR #161:
URL: https://github.com/apache/datafusion-site/pull/161#discussion_r2976294986
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content/blog/2026-03-20-writing-table-providers.md:
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+---
+layout: post
+title: Writing Custom Table Providers in Apache DataFusion
+date: 2026-03-20
+author: Tim Saucer (rerun.io)
+categories: [tutorial]
+---
+<!--
+{% comment %}
+Licensed to the Apache Software Foundation (ASF) under one or more
+contributor license agreements. See the NOTICE file distributed with
+this work for additional information regarding copyright ownership.
+The ASF licenses this file to you under the Apache License, Version 2.0
+(the "License"); you may not use this file except in compliance with
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+
+http://www.apache.org/licenses/LICENSE-2.0
+
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+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+{% endcomment %}
+-->
+
+[TOC]
+
+One of DataFusion's greatest strengths is its extensibility. If your data lives
+in a custom format, behind an API, or in a system that DataFusion does not
+natively support, you can teach DataFusion to read it by implementing a
+**custom table provider**. This post walks through the three layers you need to
+understand and explains where your work should actually happen.
+
+## The Three Layers
+
+---
+
+When DataFusion executes a query against a table, three abstractions
collaborate
+to produce results:
+
+1. **[`TableProvider`]** -- Describes the table (schema, capabilities) and
+ produces an execution plan when queried.
+2. **[`ExecutionPlan`]** -- Describes *how* to compute the result:
partitioning,
+ ordering, and child plan relationships.
+3. **[`SendableRecordBatchStream`]** -- The async stream that *actually does
the
+ work*, yielding `RecordBatch`es one at a time.
+
+Think of these as a funnel: `TableProvider::scan()` is called once during
+planning to create an `ExecutionPlan`, then `ExecutionPlan::execute()` is
called
+once per partition to create a stream, and those streams are where rows are
+actually produced during execution.
Review Comment:
Added a section about the planning stages.
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