Need assitance with high memory usage on Azure Managed Redis B150 cache

Question

We currently have 2 caches.

One for all MSFT users which is a B3 and another for all users which is B150.

Both of the caches store the same style document.  A single document size in 550 bytes.

The MSFT cache has 180K keys and its memory usage is at 250MB which is aligned with the # of keys.

They global cache B150 has 21M keys as is already at 26GB usage. For the 21M keys we would have expected around 11-15GB usage with the overhead but not 26GB. Need assistance with the memory break down and to see where the additional memory is being consumed.

INFO MEMORY# Memory used_memory:27949194144 used_memory_human:26.2G used_memory_rss:27949194144 used_memory_peak:27973816144 used_memory_peak_human:26.5G used_memory_lua:5406720 maxmemory_policy:noeviction mem_fragmentation_ratio:1 mem_allocator:jemalloc-5.3.0

Answer 1

Hi Fahad Hayat,
The missing detail was that Azure Managed Redis memory metrics are effectively calculated x2 when High Availability is enabled.

Azure Managed Redis uses a primary and replica architecture. All data stored on the primary node is replicated to the replica node, and Azure reports memory usage across both nodes. As a result, the total reported memory includes replication overhead, which explains why ~11–13 GB of actual data appears as ~26 GB usage.
References:

• High availability for Azure Cache for Redis
• Azure Managed Redis architecture