How should I set maxmemory-reserved and maxfragmentmemory-reserved in the Redis Cache?

ZP@Gyrus 20

Hi. I'm dealing with a web app that is having issues with it's Redis Cache, so my company's IT team is wanting me to inquire as to whether increasing the maxmemory-reserved and the maxfragmentationmemory-reserved settings under our Redis Cache Advanced settings would help. In other words, how would we determine the best settings to set here? Max Memory Advanced Settings

Mallaiah Sangi 85 Reputation points Microsoft Vendor

2025-02-25T21:24:20.0533333+00:00

Hi @ZP@Gyrus

Thanks for the Question and using Microsoft Q&A

As per my understanding, setting up maxmemory-reserved and maxfragmentmemory-reserved in the Redis Cache for better performance.

Memory policies:

Use the Maxmemory policy, maxmemory-reserved, and maxfragmentationmemory-reserved settings from Advanced settings from the Resource menu on the left to configure the memory policies for the cache. When you create a cache, the values maxmemory-reserved and maxfragmentationmemory-reserved default to 10% of maxmemory, which is the cache size.

find the below link for better understanding of Memory configuration.

https://learn.microsoft.com/en-us/azure/azure-cache-for-redis/cache-configure?tabs=access-keys

maxmemory-reserved setting configures the amount of memory in MB per instance in a cluster that is reserved for noncache operations, such as replication during failover. Setting this value allows you to have a more consistent Redis server experience when your load varies. This value should be set higher for workloads that write large amounts of data. When memory is reserved for such operations, it's unavailable for storage of cached data. The minimum and maximum values on the slider are 10% and 60%, shown in megabytes. You must set the value in that range.

maxfragmentationmemory-reserved setting configures the amount of memory in MB per instance in a cluster that is reserved to accommodate for memory fragmentation. When you set this value, the Redis server experience is more consistent when the cache is full or close to full and the fragmentation ratio is high. When memory is reserved for such operations, it's unavailable for storage of cached data. The minimum and maximum values on the slider are 10% and 60%, shown in megabytes. You must set the value in that range.

When choosing a new memory reservation value (maxmemory-reserved or maxfragmentationmemory-reserved), consider how this change might affect a cache that is already running with large amounts of data in it. For instance, if you have a 53-GB cache with 49 GB of data, then change the reservation value to 8 GB, this change drops the max available memory for the system down to 45 GB. If either your current used_memory or your used_memory_rss values are higher than the new limit of 45 GB, then the system has to evict data until both used_memory and used_memory_rss are below 45 GB. Eviction can increase server load and memory fragmentation. For more information on cache metrics such as used_memory and used_memory_rss.

I hope this information helps. Please do let us know if you have any further queries.
Mallaiah Sangi 85 Reputation points Microsoft Vendor

2025-02-26T21:27:16.03+00:00

Hi @ZP@Gyrus

We haven’t heard from you on the last response and was just checking back to see if you have a resolution yet. In case if you have any resolution please do share that same with the community as it can be helpful to others. Otherwise, will respond with more details and we will try to help.
ZP@Gyrus 20 Reputation points

2025-02-26T21:31:30.1466667+00:00

Thanks for your response, Mallaih.

I appreciate the follow-up. I'm still checking this out and will be sure to update the thread when I'm done.
Mallaiah Sangi 85 Reputation points Microsoft Vendor

2025-02-27T21:52:26.23+00:00

Hi ZP@Gyrus

We haven’t heard from you on the last response and was just checking back to see if you have a resolution yet. In case if you have any resolution please do share that same with the community as it can be helpful to others. Otherwise, will respond with more details and we will try to help

1 answer

ZP@Gyrus 20 Reputation points

2025-02-28T16:38:21.45+00:00

Hi Mallaiah,

Thanks for waiting, I'm still learning about how the Redis Cache works so please pardon me taking a little extra time to review this. If I am understanding this correctly, then having higher maxmemory-reserved means better performance for large data writes, but less storage capacity. Higher maxfragmentationmemory-reserved means better consistency when the cache is full, but less storage space, correct?

If I may ask your opinion, if we're having large response sizes and have inconsistent application behavior, would we want to raise these settings up for better performance or instead focus on conserving storage space?
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