How to effectively stay in-sync when using dfuse streaming API

Question

I'm using dfuse streaming API to built a EOS based application. I want to keep an in-sync view of all the data flowing through my smart contract.

I want to ensure that I will always be in sync so I never miss a single block. Using the dfuse streaming API, how can I achieve that?

Answer 1

Using the with_progress feature of the Websocket API, you will receive one progress message after each block was processed.

For a given stream (corresponding to a request and an associated req_id), when you received a progress for a block, you are guaranteed to have seen all the contents it contained in your query (the actions for get_action_traces, or the rows for get_table_rows).

If you keep track of that block_num and/or block_id, upon disconnection/reconnections, you can provide it back in your request, and be guaranteed never to miss a beat, even if that means you're reprocessing 1M blocks.

As of November 22nd 2018, the get_table_rows request will stream table_delta messages that include an "undo"/"redo" step. This allows your app to navigate forks and ensure absolute sync of your application with the longest chain's state.

Check the docs at https://docs.dfuse.io/ and search for with_progress for more details.