RS: new Flex docs #2871
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| --- | ||
| Title: Flex databases | ||
| alwaysopen: false | ||
| categories: | ||
| - docs | ||
| - operate | ||
| - rs | ||
| - rc | ||
| description: Extend Redis databases with flash storage for large-scale, cost-efficient deployments. | ||
| hideListLinks: true | ||
| linktitle: Flex databases | ||
| weight: 38 | ||
| --- | ||
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| Flex extends your database capacity by combining RAM and flash (SSD) storage. This tiered architecture keeps frequently accessed (hot) data in RAM for sub-millisecond latency while storing less active (warm) data on flash to reduce costs and increase capacity. Flex frees RAM for hot data, leads to a higher RAM hit rate, and allows bigger datasets per node. | ||
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| Flex databases work with your existing Redis applications and the Redis API without modification. | ||
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| ## How Flex works | ||
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| ### Automatic data tiering | ||
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| Flex moves data between RAM and flash based on access patterns: | ||
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| - Frequently accessed data stays in high-speed RAM. | ||
| - Less active data moves to cost-efficient flash storage. | ||
| - Data accessed from flash promotes back to RAM automatically. | ||
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| Redis uses an [LRU (least recently used)]({{< relref "/develop/reference/eviction#apx-lru" >}}) eviction policy to manage data placement. When memory pressure increases, Flex identifies cold objects, transfers them to flash, and frees RAM for new or frequently accessed keys. | ||
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| This process requires no application changes. Your existing Redis commands work across both storage tiers. | ||
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| ### Storage engine | ||
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| Flex uses [Speedb](https://docs.speedb.io), a high-performance key-value storage engine optimized for flash drives: | ||
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| - Redis handles all data operations in memory. | ||
| - Speedb manages the flash storage layer. | ||
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| This design delivers predictable latency and throughput as datasets grow beyond RAM limits. | ||
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| ## Compatibility | ||
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| Flex is compatible with the Redis API and supports all Redis data types, including JSON and probabilistic data structures (Bloom filters, Count-Min Sketch, Top-K). | ||
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| The following features are not yet supported with Flex: | ||
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| - Redis Search | ||
| - Time series | ||
| - Active-Active | ||
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| ## When to use Flex | ||
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| Use Flex when you need to: | ||
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| - Run Redis at terabyte scale while maintaining high throughput and sub-10 ms latency | ||
| - Power real-time feature stores for machine learning applications | ||
| - Operate large distributed caches with elastic scaling and consistent performance under heavy load | ||
| - Reduce infrastructure costs by combining high-speed RAM with cost-efficient flash storage | ||
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| {{<note>}} | ||
| Flex does not replace long-term data persistence. For workloads that require durability and recovery across restarts or failures, use Redis persistence features like [AOF (Append-Only File)]({{< relref "/operate/oss_and_stack/management/persistence#append-only-file" >}}), [RDB snapshots]({{< relref "/operate/oss_and_stack/management/persistence#snapshotting" >}}), or both. For more information, see [Database persistence]({{< relref "/operate/rs/databases/configure/database-persistence" >}}). | ||
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There was a problem hiding this comment. I suggest adding a dedicated "What Flex isn't" section with the wording similar to the doc: https://docs.google.com/document/d/1PuFejCooJpy_gs0MoM5Pf9MLS46x6gcNUmzYfPjIHik/edit?disco=AAABz_t08H0&tab=t.0
Collaborator
Author
There was a problem hiding this comment. This info is already included in a note in https://redis.io/docs/staging/DOC-6284/operate/rs/flex/#when-to-use-flex:
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| {{</note>}} | ||
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| ## Flex and Auto Tiering | ||
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| Flex replaces [Auto Tiering]({{< relref "/operate/rs/7.22/databases/auto-tiering" >}}) (formerly known as Redis on Flash). Redis Software selects the implementation based on your Redis version: | ||
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| | Redis database version | Flex | Auto Tiering | | ||
| |------------------------|------|--------------| | ||
| | 8.0 and later | <span title="Supported">✅</span> | <span title="Not supported">❌</span> | | ||
| | 7.4 | <span title="Supported">✅</span> | <span title="Supported">✅</span>| | ||
| | 7.2 and earlier | <span title="Not supported">❌</span> | <span title="Supported">✅</span> | | ||
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| For Redis Software version 7.22.2-22 or earlier, see [Auto Tiering]({{< relref "/operate/rs/7.22/databases/auto-tiering" >}}). | ||
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| ### Differences between Flex and Auto Tiering | ||
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| - Key and value offloading | ||
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There was a problem hiding this comment. Add a short explanation on why it matters: |
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| - Auto Tiering offloads only values to flash while keys remain in RAM. | ||
| - Flex offloads both keys and values, which increases dataset density per node and reduces RAM consumption. This change frees RAM for hot data, leads to a higher RAM hit rate, and allows bigger datasets per node. | ||
| - RAM population strategy | ||
| - Auto Tiering fills all available RAM before offloading data to flash. This maximizes hot-data performance but can cause non-linear performance changes at high utilization. | ||
| - Flex uses utilization-aware RAM population. When database utilization is below 50%, Flex uses up to 50% of configured RAM for hot data. Above 50% utilization, Flex uses both RAM and flash proportionally, following the configured RAM-to-flash ratio. This provides a stable performance curve, consistent RAM hit-rate, and predictable throughput and latency. | ||
| - Storage engine | ||
| - Auto Tiering uses either RocksDB or Speedb as the storage engine. | ||
| - Flex uses Speedb only. | ||
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| ## Next steps | ||
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| - [Plan your deployment]({{< relref "/operate/rs/flex/plan" >}}): Review hardware requirements, sizing guidelines, and limitations. | ||
| - [Get started]({{< relref "/operate/rs/flex/get-started" >}}): Configure Flex on your cluster. | ||
| - [Scale your deployment]({{< relref "/operate/rs/flex/scale" >}}): Learn scaling strategies and best practices. | ||
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"Flex frees RAM for hot data, higher RAM hit‑rate, bigger datasets per node”
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Added