Redis Caching & Messaging (Pub/Sub, Streams) · レッスン

Redis Streams とは？

強力で永続的なメッセージキューとしての Redis Streams のアーキテクチャとメリットを理解します。

レッスン 1/411 ステップ

「Redis Streams とは？」はCoddyKit上の無料Redis Caching & Messaging (Pub/Sub, Streams)レッスンです。これはレッスン1/4です。下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。これはRedis Caching & Messaging (Pub/Sub, Streams)学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 Redis Caching & Messaging (Pub/Sub, Streams)コースには全4レッスンが含まれています。

このレッスンの一部はまだ翻訳されておらず、英語で表示されています。

What are Redis Streams?

Welcome! In this lesson, we'll dive into Redis Streams, a powerful data structure for managing real-time event data.

Think of a stream as an append-only log of messages, similar to a traditional message queue or a Kafka topic, but built right into Redis.

Streams are ideal for building event-driven architectures, processing sensor data, or tracking user activity.

Streams vs. Pub/Sub

Redis already has Pub/Sub, so why Streams?

Persistence: Stream messages are stored and not lost if consumers are offline. Pub/Sub messages are fire-and-forget.
Consumer Groups: Streams support consumer groups for cooperative message processing, allowing multiple applications to read the same stream without duplicating work.
Message History: You can read messages from any point in the stream's history.

Streams offer durability and advanced consumption patterns that Pub/Sub doesn't.

Stream Architecture: Entries & IDs

A Redis Stream is an ordered sequence of entries. Each entry is composed of:

A unique Stream ID: This is a timestamp-based ID (e.g., 1678886400000-0) that ensures messages are strictly ordered.
One or more field-value pairs: These are the actual data for the message, similar to a small Redis Hash.

Think of it as a log where each line has a unique timestamp and some key-value data.

Adding Entries with XADD

Producers add new entries to a stream using the XADD command. Redis automatically generates a unique ID for each new entry, or you can provide one.

The * wildcard tells Redis to generate a new, unique ID for the entry.

Try running this example:

public class Main {
  public static void main(String[] args) {
    System.out.println("Simulating Redis XADD command:");
    String streamName = "sensor_data";
    
    // XADD sensor_data * temp 25 hum 60
    System.out.println("redisClient.xadd(");
    System.out.println("  \"" + streamName + "\", \"*\",");
    System.out.println("  \"temp\", \"25\", \"hum\", \"60\"");
    System.out.println(");");
    System.out.println("\nOutput (example ID): 1678886400000-0");
  }
}

Understanding Stream IDs

Stream IDs have two parts: <milliseconds-timestamp>-<sequence-number>.

The timestamp is the time the entry was added (in Unix milliseconds).
The sequence number is incremented if multiple entries are added within the same millisecond.

This structure guarantees that IDs are always increasing, providing a natural order for messages. You can use 0-0 to refer to the very beginning of a stream.

Reading from a Stream with XREAD

Consumers use the XREAD command to retrieve entries from one or more streams. You specify the stream name and the ID from which to start reading.

XREAD allows you to fetch a batch of messages, making it efficient for consumers.

Try running this example:

public class Main {
  public static void main(String[] args) {
    System.out.println("Simulating Redis XREAD command:");
    String streamName = "sensor_data";
    String startId = "0-0"; // Read from the beginning
    
    // XREAD STREAMS sensor_data 0-0
    System.out.println("List<Map<String, String>> entries =");
    System.out.println("  redisClient.xread("STREAMS",");
    System.out.println("  \"" + streamName + "\", \"" + startId + "\"");
    System.out.println(");");
    
    System.out.println("\nExample Output:");
    System.out.println("ID: 1678886400000-0, {temp=25, hum=60}");
    System.out.println("ID: 1678886400001-0, {temp=26, hum=61}");
  }
}

Blocking Reads for Real-time

To read new messages as they arrive, you can use the BLOCK option with XREAD. This makes the command wait for new data if no new entries are available.

You can also specify a timeout for the blocking operation. This is crucial for building real-time applications that react instantly to events.

Example: XREAD BLOCK 0 STREAMS mystream $ ($ means 'last ID in stream').

Stream Persistence & History

Unlike Pub/Sub, Redis Streams are persistent. Messages added to a stream remain there until explicitly removed or trimmed.

This allows new consumers to read the entire history of events from the beginning, or catch up from a specific point if they were temporarily offline.

This persistence is a key feature for reliable event logging and replay capabilities.

Ordered & Immutable Entries

Redis Streams guarantee that entries are always added in the order they are received and assigned strictly incrementing IDs.

Once an entry is added to a stream, it cannot be modified. This immutability is fundamental for maintaining an accurate, auditable log of events.

These properties make Streams excellent for event sourcing and ensuring data consistency.

Check Your Understanding

Which of the following are key benefits or characteristics of Redis Streams?

対話的なレッスンで答える

Recap: What are Redis Streams?

In this lesson, we learned that Redis Streams are a powerful, persistent, append-only log data structure.

They offer persistence, ordered delivery, and support for consumer groups, differentiating them from Pub/Sub.
We explored how to add entries with XADD and read them with XREAD.
Streams are ideal for event sourcing, real-time data processing, and building reliable message queues.

Next, we'll dive deeper into Stream commands and features!

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よくある質問

「Redis Streams とは？」レッスンは無料ですか？

はい。「Redis Streams とは？」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、Redis Caching & Messaging (Pub/Sub, Streams)コースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 Redis Caching & Messaging (Pub/Sub, Streams)コースには全4レッスンが含まれています。

「Redis Streams とは？」で何を学びますか？

強力で永続的なメッセージキューとしての Redis Streams のアーキテクチャとメリットを理解します。ブラウザで直接実行するハンズオンコードでRedis Caching & Messaging (Pub/Sub, Streams)を演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。

Redis Caching & Messaging (Pub/Sub, Streams)を始めるのに経験は必要ですか？

事前経験は必要ありません。CoddyKitのRedis Caching & Messaging (Pub/Sub, Streams)は初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。これはレッスン1/4です。

「Redis Streams とは？」レッスンにはどのくらい時間がかかりますか？

ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。

このRedis Caching & Messaging (Pub/Sub, Streams)レッスンでコードを書いて実行できますか？

はい。すべてのRedis Caching & Messaging (Pub/Sub, Streams)レッスンに組み込みコードエディタが含まれているため、ブラウザでリアルコードを書いて実行し、即座のAIフィードバックを取得できます。ローカル設定は不要です。

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