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# SessionContext

`SessionContext` is the entry point into DataFusion from Java. It owns the
catalog of registered tables and the query planner.

## Lifecycle

```java
try (SessionContext ctx = new SessionContext()) {
    // register tables, build queries...
}
```

`SessionContext` is `AutoCloseable`. Closing it releases the underlying
native context. Use `try`-with-resources so the native side is freed even
on exception.

## Threading

A `SessionContext` is **not thread-safe**. Do not share one across threads
without external synchronization. The simplest pattern is one context per
thread.

## Configuration

`SessionContext.builder()` exposes a fluent builder for overriding
DataFusion defaults — batch size, target partitions, statistics
collection, information schema, memory pool size, and the spill
directory. See the
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<a href="../api/org/apache/datafusion/SessionContextBuilder.html"><code>SessionContextBuilder</code></a>
Javadoc for the full list.

```java
try (SessionContext ctx = SessionContext.builder()
        .batchSize(4096)
        .targetPartitions(8)
        .build()) {
    // ...
}
```

## Spark-compatible functions

`withSparkFunctions()` registers Apache Spark–compatible functions and
expression planners (from the
[`datafusion-spark`](https://crates.io/crates/datafusion-spark) crate) on the
context:

```java
try (SessionContext ctx = SessionContext.builder()
        .withSparkFunctions()
        .build();
     DataFrame df = ctx.sql("SELECT crc32('Spark')")) {
    // ...
}
```

When enabled, Spark-compatible functions override any DataFusion built-in of
the same name. This requires the native library to be built with the `spark`
Cargo feature, which is enabled in the default build; otherwise `build()`
throws explaining the feature is missing.