![]() ![]() Before Redis 7.0.1 PUBLISH, SPUBLISH and PFCOUNT were not considered write commands in scripts.Read-only scripts and read-only script commands were introduced in Redis 7.0 Many clients also better support routing the read-only script commands to replicas for applications that want to use replicas for read scaling.They can be used to configure an ACL user to only be able to execute read-only scripts.In addition to the benefits provided by all read-only scripts, the read-only script commands have the following advantages: Currently PUBLISH, SPUBLISH and PFCOUNT are also considered write commands in scripts, because they could attempt to propagate commands to replicas and AOF file.They cannot execute any command that may modify the data set.They are not blocked during write pauses, such as those that occur during coordinated failovers.They never fail with OOM error when redis is over the memory limit.They can always be killed by the SCRIPT KILL command.They can always be executed on replicas.Read-only scripts can be executed either by adding the no-writes flag to the script or by executing the script with one of the read-only script command variants: EVAL_RO, EVALSHA_RO, or FCALL_RO. Read-only scriptsĪ read-only script is a script that only executes commands that don't modify any keys within Redis. However, if you intend to use a slow script in your application, be aware that all other clients are blocked and can't execute any command while it is running. It is not hard to create fast scripts because scripting's overhead is very low. Note that the potential downside of this blocking approach is that executing slow scripts is not a good idea. The blocking semantics of an executed script apply to all connected clients at all times. These semantics mean that all of the script's effects either have yet to happen or had already happened. The script's execution blocks all server activities during its entire time, similarly to the semantics of transactions. When running a script or a function, Redis guarantees its atomic execution. Please refer to the following pages for more information: In this case, loading a function to the database becomes an administrative deployment task (such as loading a Redis module, for example), which separates the script from the application. To use functions, they need to be loaded first, and then they are available for use by all connected clients. Secondly, added in v7.0, Redis Functions are essentially scripts that are first-class database elements.Īs such, functions decouple scripting from application logic and enable independent development, testing, and deployment of scripts. That is because scripts are only cached by the server and are volatile.Īs your application grows, this approach can become harder to develop and maintain. However, using them means that the scripted logic is a part of your application (not an extension of the Redis server).Įvery applicative instance that runs a script must have the script's source code readily available for loading at any time. Redis provides two means for running scripts.įirstly, and ever since Redis 2.6.0, the EVAL command enables running server-side scripts.Įval scripts provide a quick and straightforward way to have Redis run your scripts ad-hoc. Please refer to the Redis Lua API Reference page for complete documentation. Presently, Redis supports a single scripting engine, the Lua 5.1 interpreter. User scripts are executed in Redis by an embedded, sandboxed scripting engine. Such APIs can encapsulate business logic and maintain a data model across multiple keys and different data structures. In our case, scripts enable processing the data where it lives, a.k.a data locality.įurthermore, the responsible embedding of programmatic workflows in the Redis server can help in reducing network traffic and improving overall performance.ĭevelopers can use this capability for implementing robust, application-specific APIs. We refer to such pieces of logic as scripts. The term programmability in Redis means having the ability to execute arbitrary user-defined logic by the server. In many cases, these commands provide all the functionality that a developer requires for managing application data in Redis. ![]() Most the commands specialize at manipulating core data types in different ways. The language that Redis speaks consists of its commands. Redis is, by definition, a "domain-specific language for abstract data types". In Redis 6.2 and below, you use Lua scripting with the EVAL command to program the server. In Redis 7 and beyond, you can use Redis Functions to manage and run your scripts. Redis provides a programming interface that lets you execute custom scripts on the server itself. Extending Redis with Lua and Redis Functions ![]()
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