Perf: SessionContainer.ResolvePartitionLocalSessionTokenForGateway triggers repeated JSON deserialization on PartitionKeyRange.Parents per request

[kirankumarkolli]

Parent issue: #5747

Problem

SessionContainer.ResolvePartitionLocalSessionTokenForGateway() (src/SessionContainer.cs:158-163) accesses PartitionKeyRange.Parents in a loop first checking if Parents != null, then iterating Parents.Count and accessing Parents[parentIndex]. Each access to .Parents triggers JToken.ToObject<Collection<string>>(), deserializing the entire collection from JSON on every access.

Hot path assessment: HOT

Called per-request when using Session consistency (the default consistency level). The method resolves session tokens for gateway-mode requests. With partition splits producing parent chains, this loop can execute multiple times per request.

Suggested fix

Cache request.RequestContext.ResolvedPartitionKeyRange.Parents in a local IReadOnlyList<string> variable before the null check and loop.

Lines

• SessionContainer.cs:158 request.RequestContext.ResolvedPartitionKeyRange.Parents != null
• SessionContainer.cs:161 request.RequestContext.ResolvedPartitionKeyRange.Parents.Count
• SessionContainer.cs:163 request.RequestContext.ResolvedPartitionKeyRange.Parents[parentIndex]

Constraint

PartitionKeyRange is in compiled NuGet (Microsoft.Azure.Cosmos.Direct) fix must be at the call site.