PostgreSQL Native Publish Subscribe

The PostgreSQL transport implements the publish-subscribe pattern. A dedicated subscription routing table, shared by all endpoints, is created to hold subscription information for each event type. When an endpoint subscribes to an event, an entry is created in the subscription routing table. When an endpoint publishes an event, the subscription routing table is queried to find all of the subscribing endpoints.

Configure subscription caching

Subscription information can be cached for a given period of time so that it does not have to be loaded every time an event is being published. The longer the cache period is, the higher the chance that new subscribers miss some events.

The default behavior is to cache subscription information for 5 seconds. This value is selected to be high enough to prevent excessive database lookups in high throughput scenarios when hundreds of messages are published each second.

If the default value is not suitable for a particular endpoint it can be changed:

var transport = new PostgreSqlTransport("connectionString")
{
    Subscriptions =
    {
        CacheInvalidationPeriod = TimeSpan.FromMinutes(1)
    }
};

In systems where events are subscribed and unsubscribed regularly, it makes sense to keep the caching period short or to disable the caching altogether:

var transport = new PostgreSqlTransport("connectionString")
{
    Subscriptions =
    {
        DisableCaching = true
    }
};

Configure subscription table

All endpoints use a single subscription table which, by default, is named SubscriptionRouting and created in the default schema of the catalog specified in the connection string. To change where this table location and/or name, use the following API:

var transport = new PostgreSqlTransport("connectionString")
{
    Subscriptions = 
    {
        SubscriptionTableName = new SubscriptionTableName(
            table: "Subscriptions", 
            schema: "OptionalSchema")
    }
};