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Document dynamic concurrency limits #128753

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14 changes: 12 additions & 2 deletions articles/azure-functions/functions-concurrency.md
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Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,7 @@ ms.custom:
- build-2024
- ignite-2024
- build-2025
ms.date: 09/02/2025
ms.date: 09/02/2026
ms.author: cachai
# customer intent: As a developer, I want to become familiar with concurrency in Azure Functions so that I know when to use which concurrency model and can optimize concurrency settings.
---
Expand Down Expand Up @@ -105,12 +105,22 @@ You can turn on dynamic concurrency in your function app by adding the following
"version": "2.0",
"concurrency": {
"dynamicConcurrencyEnabled": true,
"maximumFunctionConcurrency": 500,
"cpuThreshold": 0.80,
"snapshotPersistenceEnabled": true
}
}
```

When `snapshotPersistenceEnabled` is `true`, which is the default value, the learned concurrency values are periodically persisted to storage. New instances start from those values instead of starting from a level of one and having to redo the learning.
The following settings control how dynamic concurrency behaves:

| Setting | Default | Description |
| --- | --- | --- |
| `maximumFunctionConcurrency` | 500 | Sets an upper limit for the concurrency that the host can learn for each function on an instance. Use a positive integer, or set the value to `-1` to remove the limit. This setting is a ceiling; it doesn't force a function to run at the configured concurrency. |
| `cpuThreshold` | 0.80 | Sets the CPU usage level at which the host's CPU health throttle can activate. Use a value greater than 0 and less than 1. For example, `0.75` represents 75 percent CPU usage. Lower values cause the host to reduce concurrency at a lower CPU usage level. |
| `snapshotPersistenceEnabled` | true | Controls whether the host periodically saves learned concurrency values to storage. New instances can start from saved values instead of starting from a concurrency of one and relearning the workload. |

The host applies `maximumFunctionConcurrency` and `cpuThreshold` only when `dynamicConcurrencyEnabled` is `true`.

### Concurrency manager

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8 changes: 7 additions & 1 deletion articles/azure-functions/functions-host-json.md
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Expand Up @@ -2,7 +2,7 @@
title: host.json reference for Azure Functions 2.x
description: Describes the various available settings for the Azure Functions host that can be set in the host.json file for the Functions v4 runtime.
ms.topic: reference
ms.date: 05/16/2024
ms.date: 09/02/2026
---

# host.json reference for Azure Functions 2.x and later
Expand Down Expand Up @@ -38,6 +38,8 @@ The following sample *host.json* file for version 2.x+ has all possible options
},
"concurrency": {
"dynamicConcurrencyEnabled": true,
"maximumFunctionConcurrency": 500,
"cpuThreshold": 0.80,
"snapshotPersistenceEnabled": true
},
"extensions": {
Expand Down Expand Up @@ -289,6 +291,8 @@ Enables dynamic concurrency for specific bindings in your function app. For more
{
"concurrency": {
"dynamicConcurrencyEnabled": true,
"maximumFunctionConcurrency": 500,
"cpuThreshold": 0.80,
"snapshotPersistenceEnabled": true
}
}
Expand All @@ -297,6 +301,8 @@ Enables dynamic concurrency for specific bindings in your function app. For more
|Property | Default | Description |
| --------- | --------- | --------- |
| dynamicConcurrencyEnabled | false | Enables dynamic concurrency behaviors for all triggers supported by this feature, which is off by default. |
| maximumFunctionConcurrency | 500 | Sets an upper limit for the concurrency that the host can learn for each function on an instance. The value must be a positive integer, or `-1` to remove the limit. This setting applies only when `dynamicConcurrencyEnabled` is `true`. |
| cpuThreshold | 0.80 | Sets the CPU usage level at which the host's CPU health throttle can activate. The value must be greater than 0 and less than 1. This setting applies only when `dynamicConcurrencyEnabled` is `true`. |
| snapshotPersistenceEnabled | true | Learned concurrency values are periodically persisted to storage so new instances start from those values instead of starting from 1 and having to redo the learning. |

## eventHub
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