> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/apache/iceberg/llms.txt
> Use this file to discover all available pages before exploring further.

# ComputePartitionStats Action

> API reference for the ComputePartitionStats action that computes and writes partition statistics

# ComputePartitionStats

The `ComputePartitionStats` action computes and writes partition statistics for an Iceberg table. This action helps optimize query planning by providing metadata about partition-level data characteristics.

## Interface

```java theme={null}
public interface ComputePartitionStats extends Action<ComputePartitionStats, ComputePartitionStats.Result>
```

## Overview

Partition statistics provide valuable metadata that query engines can use to optimize execution plans. The action:

* Computes statistics for partitions in a table snapshot
* Writes statistics to a dedicated statistics file
* Uses the current snapshot by default
* Can target a specific snapshot if needed

## Methods

### snapshot

Choose a specific table snapshot to compute partition statistics.

```java theme={null}
ComputePartitionStats snapshot(long snapshotId)
```

**Parameters:**

* `snapshotId` - The ID of the snapshot for which stats need to be computed

**Returns:** `this` for method chaining

**Example:**

```java theme={null}
action.snapshot(1234567890L);
```

<Note>
  If not specified, the action uses the current snapshot of the table.
</Note>

## Result

The `Result` interface provides information about the computed statistics.

### Methods

```java theme={null}
interface Result {
  PartitionStatisticsFile statisticsFile();
}
```

#### statisticsFile

Returns the statistics file that was written, or `null` if no statistics were collected.

**Returns:** `PartitionStatisticsFile` or `null`

## Usage Examples

### Compute Stats for Current Snapshot

```java theme={null}
// Compute partition statistics for the current snapshot
ComputePartitionStats.Result result = actions
  .computePartitionStats(table)
  .execute();

PartitionStatisticsFile statsFile = result.statisticsFile();
if (statsFile != null) {
  System.out.println("Statistics file: " + statsFile.path());
  System.out.println("Snapshot ID: " + statsFile.snapshotId());
}
```

### Compute Stats for Specific Snapshot

```java theme={null}
// Compute partition statistics for a specific snapshot
long targetSnapshotId = table.currentSnapshot().parentId();

ComputePartitionStats.Result result = actions
  .computePartitionStats(table)
  .snapshot(targetSnapshotId)
  .execute();

if (result.statisticsFile() != null) {
  System.out.println("Computed stats for snapshot: " + targetSnapshotId);
}
```

### Check Statistics File Details

```java theme={null}
// Compute stats and examine the results
ComputePartitionStats.Result result = actions
  .computePartitionStats(table)
  .execute();

PartitionStatisticsFile statsFile = result.statisticsFile();
if (statsFile != null) {
  System.out.println("Statistics Details:");
  System.out.println("  Path: " + statsFile.path());
  System.out.println("  Snapshot: " + statsFile.snapshotId());
  System.out.println("  Size: " + statsFile.fileSizeInBytes() + " bytes");
} else {
  System.out.println("No statistics were collected");
}
```

## Best Practices

1. **Compute after significant data changes**: Run this action after major writes or rewrites to keep statistics current

2. **Use with query optimization**: Ensure your query engine is configured to use partition statistics

3. **Monitor statistics freshness**: Outdated statistics may lead to suboptimal query plans

4. **Consider snapshot selection**: For historical analysis, compute stats on specific snapshots

<Note>
  Partition statistics are most beneficial for partitioned tables with selective query patterns.
</Note>

## Related

* [ComputeTableStats](/api/actions/compute-table-stats) - Compute table-level statistics
* [ExpireSnapshots](/api/actions/expire-snapshots) - Manage old snapshots
* [RewriteDataFiles](/api/actions/rewrite-data-files) - Optimize data file layout