# Pipelines and transactions ```json metadata { "schema_version": 2, "title": "Pipelines and transactions", "description": "Learn how to use Redis pipelines and transactions", "categories": ["docs","develop","stack","oss","rs","rc","oss","kubernetes","clients"], "tableOfContents": {"sections":[{"id":"execute-a-pipeline","title":"Execute a pipeline"},{"id":"execute-a-transaction","title":"Execute a transaction"},{"id":"watch-keys-for-changes","title":"Watch keys for changes"}]} , "codeExamples": [{"codetabsId":"pipe_trans_tutorial-stepbasic_pipe","description":"Foundational: Batch multiple Lettuce commands and flush them to the server together","difficulty":"beginner","id":"basic_pipe","languages":[{"clientId":"lettuce","clientName":"Lettuce","id":"Lettuce-Sync","langId":"java","panelId":"panel_Lettuce-Sync_pipe_trans_tutorial-stepbasic_pipe"},{"clientId":"lettuce","clientName":"Lettuce","id":"Java-Async","langId":"java","panelId":"panel_Java-Async_pipe_trans_tutorial-stepbasic_pipe"},{"clientId":"lettuce","clientName":"Lettuce","id":"Java-Reactive","langId":"java","panelId":"panel_Java-Reactive_pipe_trans_tutorial-stepbasic_pipe"}]},{"codetabsId":"pipe_trans_tutorial-stepbasic_trans","description":"Foundational: Use MULTI and EXEC with Lettuce to execute multiple commands atomically","difficulty":"beginner","id":"basic_trans","languages":[{"clientId":"lettuce","clientName":"Lettuce","id":"Lettuce-Sync","langId":"java","panelId":"panel_Lettuce-Sync_pipe_trans_tutorial-stepbasic_trans"},{"clientId":"lettuce","clientName":"Lettuce","id":"Java-Async","langId":"java","panelId":"panel_Java-Async_pipe_trans_tutorial-stepbasic_trans"},{"clientId":"lettuce","clientName":"Lettuce","id":"Java-Reactive","langId":"java","panelId":"panel_Java-Reactive_pipe_trans_tutorial-stepbasic_trans"}]},{"codetabsId":"pipe_trans_tutorial-steptrans_watch","description":"Optimistic locking: Use WATCH with EXEC and check whether Lettuce discarded the transaction","difficulty":"intermediate","id":"trans_watch","languages":[{"clientId":"lettuce","clientName":"Lettuce","id":"Lettuce-Sync","langId":"java","panelId":"panel_Lettuce-Sync_pipe_trans_tutorial-steptrans_watch"},{"clientId":"lettuce","clientName":"Lettuce","id":"Java-Async","langId":"java","panelId":"panel_Java-Async_pipe_trans_tutorial-steptrans_watch"},{"clientId":"lettuce","clientName":"Lettuce","id":"Java-Reactive","langId":"java","panelId":"panel_Java-Reactive_pipe_trans_tutorial-steptrans_watch"}]}] } ``` ## Code Examples Legend The code examples below show how to perform the same operations in different programming languages and client libraries: - **Redis CLI**: Command-line interface for Redis - **C# (Synchronous)**: StackExchange.Redis synchronous client - **C# (Asynchronous)**: StackExchange.Redis asynchronous client - **Go**: go-redis client - **Java (Synchronous - Jedis)**: Jedis synchronous client - **Java (Asynchronous - Lettuce)**: Lettuce asynchronous client - **Java (Reactive - Lettuce)**: Lettuce reactive/streaming client - **JavaScript (Node.js)**: node-redis client - **PHP**: Predis client - **Python**: redis-py client - **Rust (Synchronous)**: redis-rs synchronous client - **Rust (Asynchronous)**: redis-rs asynchronous client Each code example demonstrates the same basic operation across different languages. The specific syntax and patterns vary based on the language and client library, but the underlying Redis commands and behavior remain consistent. --- Redis lets you send a sequence of commands to the server together in a batch. There are two types of batch that you can use: - **Pipelines** avoid network and processing overhead by sending several commands to the server together in a single communication. The server then sends back a single communication with all the responses. See the [Pipelining](https://redis.io/docs/latest/develop/using-commands/pipelining) page for more information. - **Transactions** guarantee that all the included commands will execute to completion without being interrupted by commands from other clients. See the [Transactions](https://redis.io/docs/latest/develop/using-commands/transactions) page for more information. ## Execute a pipeline With Lettuce, you pipeline commands by buffering them on the client and then flushing them to the server together. The synchronous and asynchronous APIs do this by temporarily disabling auto-flushing with `setAutoFlushCommands()` and then calling `flushCommands()`; each buffered command returns a `RedisFuture` that you can inspect after the batch is flushed. The reactive API pipelines commands by composing the corresponding `Mono` and `Flux` publishers: Foundational: Batch multiple Lettuce commands and flush them to the server together **Difficulty:** Beginner **Available in:** Java, Java (Asynchronous - Lettuce), Java (Reactive - Lettuce) ##### Java ```java // Lettuce pipelines commands by buffering them on the client while // auto-flushing is disabled. Use the asynchronous API to obtain a // `RedisFuture` for each buffered command, then read the results // after the batch has been flushed to the server. RedisAsyncCommands async = connection.async(); connection.setAutoFlushCommands(false); for (int i = 0; i < 5; i++) { async.set("seat:" + i, "#" + i); } RedisFuture seat0 = async.get("seat:0"); RedisFuture seat3 = async.get("seat:3"); RedisFuture seat4 = async.get("seat:4"); connection.flushCommands(); connection.setAutoFlushCommands(true); System.out.println(seat0.get()); // >>> #0 System.out.println(seat3.get()); // >>> #3 System.out.println(seat4.get()); // >>> #4 ``` ##### Java (Asynchronous - Lettuce) ```java // Disable auto-flushing to buffer the commands on the client, then // flush them to the server as a single batch. Each command returns // a `RedisFuture` that completes when its response arrives. connection.setAutoFlushCommands(false); for (int i = 0; i < 5; i++) { async.set("seat:" + i, "#" + i); } RedisFuture seat0 = async.get("seat:0"); RedisFuture seat3 = async.get("seat:3"); RedisFuture seat4 = async.get("seat:4"); connection.flushCommands(); connection.setAutoFlushCommands(true); System.out.println(seat0.get()); // >>> #0 System.out.println(seat3.get()); // >>> #3 System.out.println(seat4.get()); // >>> #4 ``` ##### Java (Reactive - Lettuce) ```java // Reactive commands are pipelined automatically: the writes below are // sent to the server back to back, then the reads are sent as a batch // once you subscribe (here, by calling `block()`). List seats = Flux.range(0, 5) .flatMap(i -> reactive.set("seat:" + i, "#" + i)) .thenMany(Flux.just("seat:0", "seat:3", "seat:4") .flatMapSequential(reactive::get)) .collectList() .block(); System.out.println(seats.get(0)); // >>> #0 System.out.println(seats.get(1)); // >>> #3 System.out.println(seats.get(2)); // >>> #4 ``` ## Execute a transaction Lettuce transactions use the Redis `MULTI` and `EXEC` commands. Commands issued between `multi()` and `exec()` are queued on the server and only run when `exec()` completes. The return value from `exec()` is a `TransactionResult` that contains the results in order: Foundational: Use MULTI and EXEC with Lettuce to execute multiple commands atomically **Difficulty:** Beginner **Available in:** Java, Java (Asynchronous - Lettuce), Java (Reactive - Lettuce) ##### Java ```java commands.multi(); commands.incrby("counter:1", 1); commands.incrby("counter:2", 2); commands.incrby("counter:3", 3); TransactionResult transResult = commands.exec(); System.out.println((Long) transResult.get(0)); // >>> 1 System.out.println((Long) transResult.get(1)); // >>> 2 System.out.println((Long) transResult.get(2)); // >>> 3 ``` ##### Java (Asynchronous - Lettuce) ```java // Commands issued between `multi()` and `exec()` are queued on the // server. Their futures only complete when `exec()` runs. async.multi(); RedisFuture counter1 = async.incrby("counter:1", 1); RedisFuture counter2 = async.incrby("counter:2", 2); RedisFuture counter3 = async.incrby("counter:3", 3); RedisFuture execResult = async.exec(); execResult.get(); System.out.println(counter1.get()); // >>> 1 System.out.println(counter2.get()); // >>> 2 System.out.println(counter3.get()); // >>> 3 ``` ##### Java (Reactive - Lettuce) ```java // Queue the commands between `multi()` and `exec()`. Subscribing to // each one inside the `multi()` callback sends it to the server, where // it is held until `exec()` runs the transaction. TransactionResult transResult = reactive.multi() .flatMap(ok -> { reactive.incrby("counter:1", 1).subscribe(); reactive.incrby("counter:2", 2).subscribe(); reactive.incrby("counter:3", 3).subscribe(); return reactive.exec(); }) .block(); System.out.println((Long) transResult.get(0)); // >>> 1 System.out.println((Long) transResult.get(1)); // >>> 2 System.out.println((Long) transResult.get(2)); // >>> 3 ``` ## Watch keys for changes Redis supports *optimistic locking* to avoid inconsistent updates to keys that several clients may modify at the same time. The basic idea is to watch for changes to any keys that you use in a transaction while you are preparing the update. If the watched keys do change, Redis discards the transaction and you must retry using the latest value from Redis. See [Transactions](https://redis.io/docs/latest/develop/using-commands/transactions) for more information about optimistic locking. The example below watches a key, reads its current value, queues an update inside `MULTI`, and then checks `TransactionResult.wasDiscarded()` after `EXEC`: Optimistic locking: Use WATCH with EXEC and check whether Lettuce discarded the transaction **Difficulty:** Intermediate **Available in:** Java, Java (Asynchronous - Lettuce), Java (Reactive - Lettuce) ##### Java ```java commands.set("shellpath", "/usr/syscmds/"); // Watch the key for changes while we prepare the update. commands.watch("shellpath"); String currentPath = commands.get("shellpath"); String newPath = currentPath + ":/usr/mycmds/"; commands.multi(); commands.set("shellpath", newPath); TransactionResult watchedResult = commands.exec(); // `exec()` returns an empty result that reports `wasDiscarded()` if // the watched key changed before the transaction ran. if (!watchedResult.wasDiscarded()) { System.out.println(commands.get("shellpath")); // >>> /usr/syscmds/:/usr/mycmds/ } ``` ##### Java (Asynchronous - Lettuce) ```java async.set("shellpath", "/usr/syscmds/").get(); // Watch the key for changes while we prepare the update. async.watch("shellpath").get(); String currentPath = async.get("shellpath").get(); String newPath = currentPath + ":/usr/mycmds/"; async.multi().get(); async.set("shellpath", newPath); TransactionResult watchedResult = async.exec().get(); // `exec()` reports `wasDiscarded()` if the watched key changed // before the transaction ran. if (!watchedResult.wasDiscarded()) { System.out.println(async.get("shellpath").get()); // >>> /usr/syscmds/:/usr/mycmds/ } ``` ##### Java (Reactive - Lettuce) ```java reactive.set("shellpath", "/usr/syscmds/").block(); // Watch the key, read its current value, then queue the update in a // transaction. `exec()` reports `wasDiscarded()` if the watched key // changed before the transaction ran. TransactionResult watchedResult = reactive.watch("shellpath") .then(reactive.get("shellpath")) .flatMap(currentPath -> reactive.multi() .flatMap(ok -> { reactive.set("shellpath", currentPath + ":/usr/mycmds/").subscribe(); return reactive.exec(); })) .block(); if (!watchedResult.wasDiscarded()) { System.out.println(reactive.get("shellpath").block()); // >>> /usr/syscmds/:/usr/mycmds/ } ```