Subscription Capacity

PubSub+ event brokers provide three levels of capacity for subscriptions: 50k, 500k, and 5M. This number represents the number of unique subscriptions that an individual event broker can keep track of, and includes all local subscriptions (of clients, queues, and topic-endpoints), as well as all remote subscriptions learned from other event brokers in the event mesh through the Multi-Node Routing (MNR) or Dynamic Message Routing (DMR) features. Unique subscriptions are subscriptions that have the same topic string, belong to the same Message VPN, and (in the case of MNR or DMR) were added to the same event broker instance. For example, if two clients connect to the same Message VPN on the same event broker, and both add the subscription a/b/c, this subscription counts as one unique subscription against the subscription limit.

Selecting your subscription capacity depends on how your PubSub+ event broker is deployed:

  • For PubSub+ software event brokers, subscription capacity depends on the configured scaling parameters. For more information, see Maximum Number of Subscriptions.

  • For PubSub+ appliances, subscription capacity is 5M for all appliance models.

  • For PubSub+ Cloud, subscription capacity depends on the service class and the corresponding service limit. For more information, see Service Class Options for Event Broker Services.

Monitoring the Subscription Usage

Solace recommends that you monitor the number of unique subscriptions for your event broker together with the Subscription Load Factor to ensure that you don't exceed the subscription limit and that you have enough resources on your event brokers available to operate correctly.

The Subscription Load Factor accounts for the number of subscriptions and the amount of internal memory resources that are consumed by these subscriptions. Because memory resource consumption depends on more than the number of subscriptions, such as subscription length and amount of repetition, the Subscription Load Factor provides a more complete indication of your subscription capacity than the number of subscriptions alone. It is exposed as the SYSTEM_ROUTING_SUBSCRIPTIONS_LOAD_FACTOR_HIGH system event with configurable thresholds. For more information about system events, see Solace PubSub+ Syslog Events. For more information about configuring thresholds, see Configuring System Event Thresholds.

Monitoring the Unique Subscription Limit

To view the current number of unique subscriptions, run the show smrp subscriptions summary command:

Monitoring the Subscription Load Factor

To view the Subscription Load Factor, expressed as a percent, run the show memory command: 

Assigning Subscription Limits To Message VPNs Or Clients

Besides assigning the system-level subscription limit as a scaling parameter, you can assign a local subscription limit to individual Message VPNs and clients (that is less than the system-level subscription limit). For more information, see Configuring Maximum Subscriptions for Message VPNs and Configuring Maximum Subscriptions for Client Profiles.

Event Mesh Considerations

If your event broker is part of an event mesh, and connected in some manner to other event brokers, the subscriptions of the other event brokers (the remote subscriptions) count against your event broker’s subscription limit. In this case, you must be aware of the following considerations:

  • If your event mesh is built using MNR, all event brokers in the event mesh learn of all subscriptions that are exported by every other event broker in the network, regardless of whether they are directly or indirectly connected by neighbor links (see Multi-Node Routing). In this case, the subscription limit of all event brokers must be the same, and must meet or exceed the combined needs of all clients and queues, no matter which event broker is hosting them.

  • If your event mesh is built using DMR, all event brokers in the same DMR cluster learn of all subscriptions that are exported by every other event broker in the same DMR cluster. In addition, if the cluster has an external link to another cluster, all subscriptions of the Message VPNs (for which there is a per-Message VPN DMR bridge configured) from the other cluster are learned (see Dynamic Message Routing). In this case, the subscription limits of all event brokers in a given DMR cluster must be the same, and must meet or exceed the combined needs of all clients and queues of all event brokers in the same DMR cluster, in addition to all clients and queues that are exposed from an adjacent DMR cluster over a DMR bridge.

  • If your event mesh includes Message VPN bridges, the subscriptions of the client and queue of the Message VPN bridge are included in the number of local subscriptions of your event broker.