> ## 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.

# Catalog Overview

> Understanding Apache Iceberg catalogs and their role in managing table metadata

## What is a Catalog?

A catalog in Apache Iceberg is a fundamental abstraction that provides:

* **Table Discovery**: Listing and locating tables within namespaces
* **Metadata Management**: Tracking table metadata and schema evolution
* **Atomic Operations**: Ensuring ACID guarantees for table commits
* **Namespace Organization**: Hierarchical organization of tables

## How Catalogs Work

Iceberg catalogs implement the `Catalog` interface, which provides core operations:

```java theme={null}
public interface Catalog {
  // Table operations
  Table createTable(TableIdentifier identifier, Schema schema, PartitionSpec spec);
  Table loadTable(TableIdentifier identifier);
  boolean dropTable(TableIdentifier identifier, boolean purge);
  void renameTable(TableIdentifier from, TableIdentifier to);
  
  // Discovery
  List<TableIdentifier> listTables(Namespace namespace);
}
```

## Available Catalog Implementations

Iceberg provides several catalog implementations for different use cases:

<CardGroup cols={2}>
  <Card title="Hive Metastore" icon="database" href="/engines/hive/overview">
    Use existing Hive metastore infrastructure
  </Card>

  <Card title="AWS Glue" icon="aws" href="/storage/aws">
    Native AWS Glue catalog integration
  </Card>

  <Card title="JDBC" icon="table" href="/catalogs/jdbc">
    Store metadata in any relational database
  </Card>

  <Card title="Nessie" icon="git-branch" href="/catalogs/nessie">
    Git-like operations with multi-table transactions
  </Card>

  <Card title="REST" icon="server" href="/api/rest/overview">
    Language-agnostic REST catalog service
  </Card>

  <Card title="Hadoop" icon="folder" href="/catalogs/custom-catalog#hadoop-configuration-access">
    File system-based catalog for development
  </Card>
</CardGroup>

## Catalog vs TableOperations

While catalogs handle table discovery and high-level operations, **TableOperations** handle the low-level metadata read/write operations:

```java theme={null}
public interface TableOperations {
  TableMetadata current();
  TableMetadata refresh();
  void commit(TableMetadata base, TableMetadata metadata);
  FileIO io();
}
```

## Choosing a Catalog

Consider these factors when selecting a catalog:

| Factor                           | Recommended Catalog       |
| -------------------------------- | ------------------------- |
| **Existing Hive infrastructure** | Hive Metastore Catalog    |
| **AWS ecosystem integration**    | Glue Catalog              |
| **High write throughput**        | Glue, DynamoDB, or Nessie |
| **Multi-table transactions**     | Nessie Catalog            |
| **Branch/tag support**           | Nessie Catalog            |
| **Relational database**          | JDBC Catalog              |
| **Cloud-agnostic**               | REST Catalog              |
| **Development/testing**          | Hadoop Catalog            |

## Namespace Management

Catalogs that implement `SupportsNamespaces` provide hierarchical organization:

```java theme={null}
// Create a namespace
catalog.createNamespace(
  Namespace.of("analytics", "sales"),
  ImmutableMap.of("owner", "data-team")
);

// List namespaces
List<Namespace> namespaces = catalog.listNamespaces();

// Load namespace metadata
Map<String, String> metadata = catalog.loadNamespaceMetadata(
  Namespace.of("analytics")
);
```

## Catalog Properties

Common catalog properties across implementations:

| Property        | Description                             |
| --------------- | --------------------------------------- |
| `warehouse`     | Root path for table data and metadata   |
| `uri`           | Connection URI for the catalog service  |
| `io-impl`       | Custom FileIO implementation class      |
| `catalog-impl`  | Custom catalog implementation class     |
| `cache-enabled` | Enable metadata caching (default: true) |

## Security Considerations

When working with encrypted tables, catalogs must:

* Store encryption key metadata securely
* Ensure key rotation is properly tracked
* Maintain audit logs for key access
* Implement proper access controls

See the [Encryption documentation](/advanced/encryption) for detailed requirements.

## Next Steps

<CardGroup cols={2}>
  <Card title="Build Custom Catalog" icon="code" href="/catalogs/custom-catalog">
    Learn how to implement your own catalog
  </Card>

  <Card title="JDBC Catalog" icon="database" href="/catalogs/jdbc">
    Use relational databases for metadata
  </Card>

  <Card title="Nessie Integration" icon="git-branch" href="/catalogs/nessie">
    Git-like versioning for your data lake
  </Card>

  <Card title="Storage Configuration" icon="hard-drive" href="/storage/fileio">
    Configure storage backends
  </Card>
</CardGroup>