Explain Heroku Connect. What is the difference between polling and push modes, and what is "write mode"?

Heroku Connect provides bi-directional data synchronization between Salesforce and a Heroku PostgreSQL database. It is used to expose Salesforce data to Heroku apps without repeated API calls.

Polling mode (Salesforce → Heroku): Heroku Connect polls Salesforce using the REST API (SOQL queries with SystemModstamp filters) to detect changes. Simple but introduces latency. Suitable for non-real-time sync needs.

Streaming/Push mode: Heroku Connect uses the Salesforce Streaming API (CometD / CDC) to receive real-time change notifications, reducing latency significantly. More complex to configure but much more responsive.

Write Mode (Heroku → Salesforce): Changes made to the PostgreSQL table can be written back to Salesforce. Heroku Connect monitors rows with a trigger for changes and uses the Salesforce REST API to upsert them. System of Record determines which side wins on conflict — Salesforce or Heroku Postgres. Over-writing from Heroku without proper conflict handling can cause data loss.