1. Feature Guide
  2. DSR Features and Functions
  3. Routing and Transaction Related Parameters in the DSR
  4. Congestion Control
  5. Egress Throttle Group (ETG) Limiting
  6. Example: DSR Connects to a Single Server Node with Multiple Connections

2.6.15.6.1 Example: DSR Connects to a Single Server Node with Multiple Connections

DSR typically connects to a single server node with more than 1 connection for redundancy (and sometimes for capacity). DSR per-connection egress throttling functionality may result in underutilization of a server node’s capacity when a subset of the DSR connections to the server node fail and the remaining connections are capable of carrying the full capacity of the server node. For example, consider the scenario depicted in the figure below where:

  • Constraint 1: Server 1 has a total capacity of X TPS.
  • Constraint 2: Server 1 can process as much as 50% of its total capacity on a single connection.
  • DSR throttles each connection to Server 1 to X/3 (addresses constraint 1 only).

Figure 2-21 DSR Per-Connection Egress Throttling


DSR Per-Connection Egress Throttling

In the above example, the per-connection egress throttling is used to limit the aggregate egress traffic rate to Server 1 (constraint 1). As a result, each of the 3 connections to Server 1 must be throttled at 1/3 of Server 1’s capacity to prevent DSR from offering a load greater than X when all 3 connections are in-service. However, if one of the connections to Server 1 fails DSR will restrict egress traffic to 2/3 of Server 1’s capacity even though the remaining two connections are be capable of carrying the entire capacity of Server 1.

The ability for DSR to throttle the aggregate egress traffic across all 3 DSR connections to Server 1 while also throttling the egress traffic on individual connections to Server 1 reduces the limitations described above. This is shown in the figure above where:

  • Constraint 1: Server 1 has a total capacity of X TPS.
  • Constraint 2: Server 1 can process as much as 50% of its total capacity on a single connection.
  • DSR throttles the aggregate egress traffic over all connections to Server 1 to X (addresses constraint 1).
  • DSR throttles each connection to Server 1 to X/2 (addresses constraint 2).

Figure 2-22 DSR Aggregate and Per-Connection Egress Throttling


DSR Aggregate and Per-Connection Egress Throttling

In the figure above, use of aggregate egress traffic rate limiting to address constraint 1 allows the per-connection egress throttling limits to be relaxed as it is being used appropriately to address the connection constraint (constraint 2).

The DSR can aggregate and distribute information about the ETG across all DA-MPs for use in routing decisions.

During Request routing, if the DSR selects a peer/connection that is a member of an ETG and determines that either the rate or pending transaction cumulative limit for that ETG has already been reached, then the DSR does not route to that peer/connection and continues to search for an acceptable peer/connection via standard DSR routing operations.

DSR utilizes the existing user-configurable response behavior in the Routing Option Set for Requests that are throttled and cannot be routed via other connections.

DSR uses standard alarming capabilities against the ETG to alert the user when limits are exceeded.