Merge pull request #2146 from redis/DOC-5120

Add resharding section to memory-limit documentation

Author: mich-elle-luna

content/operate/rs/databases/memory-performance/memory-limit.md

@@ -79,6 +79,32 @@ Databases should return to their configured memory limits after data is removed
 
 If you observe this behavior, consider [monitoring]({{< relref "/operate/rs/monitoring/" >}}) memory usage and controlling the traffic load on the application side.
 
+## Resharding duration factors
+
+Resharding enables you to increase database capacity by adding shards and utilizing more cluster memory. Understanding resharding duration helps you plan maintenance operations and minimize database risk.
+
+### Resharding overview
+
+Resharding follows a three-stage process for each new shard:
+
+1. **Shard creation**: Creates a new shard and performs partial synchronization based on assigned hash slots
+2. **Key trimming**: Removes keys from the original shard according to new hash slot assignments
+3. **Defragmentation**: Executes failovers to optimize new shard performance
+
+When resharding multiple shards (for example, expanding from 4 to 8 shards), this process runs serially for each new shard. The operation completes only after all stages finish for every shard.
+
+{{< note >}}
+Resharding is an atomic operation that cannot be interrupted. Database corruption can occur if the process fails or stops unexpectedly. Minimizing resharding time reduces this risk.
+{{< /note >}}
+
+### Resharding duration factors
+
+Resharding duration increases linearly with the number of keys in your database. Key length and network traffic affect resharding duration:
+
+Key length directly affects resharding duration. Longer keys (2000 KB) require more time to process due to increased hash calculation overhead per key compared to short keys (10 bytes). 
+
+Network traffic has a measurable but limited effect on resharding duration. Since resharding operations typically don't reach CPU limits, the impact on both resharding time and ongoing traffic remains minimal.
+
 ## Memory metrics
 
 The Cluster Manager UI provides metrics that can help you evaluate your memory use.