We are using the official OPAL postgres data fetcher (link). When the opal client is being spun up, it will fetch the data from the postgres instance it is connected to. We are concerned that during that spin up phase if any updates to the data source happens how is it handled.

Once connected the OPAL-client will start tracking data update events that you send and handle them. It does so from the start even before getting the first base data - and will process the events in order (So you don’t need to track them specifically). To your sub question -

Does the client fetches the update messages from opal server and re runs them after it builds the initial state?

the client doesn’t re-run, but more correctly spins tasks to update as events come, and processes them once possible. Usually loading the client is pretty fast, so we haven’t encountered issues here. In general this is not a pure OPAL problem but a general multiprocess read/write sync challenge If it is an issue for you , I can suggest a few options: • Create a clone source where clients get their base data set, instead of working directly with the rapidly changing data source (this can be another OPA+OPAL instance for example - kinda like a master node) • Temporarily lock access to the DB for writing until the client is ready (reader/writer lock pattern) CC: @Filip (add these to the new FAQ, please)