Heroku Connect is a service offered by Heroku which performs 2-way data synchronization between Salesforce and a Heroku Postgres database.
When we first built Heroku Connect, we decided to use polling to determine when data had changed on either side. Polling isn't pretty, but its simple and reliable, and those are "top line" features for Heroku Connect. But polling incurs two significant costs: high latency and wasted resources. The more you poll the more you waste API calls and database queries checking when there are no data changes. But if you lengthen your polling interval then you grow the latency for the data synchronization.