MySQL CDC to BigQuery: what periodic syncs miss, and how binlog avoids it
erathos.com
erathos.com
It seems like a relatively straightforward marketing article. I was pleasantly surprised to learn about Erathos though, nice product!
I am personally not a big fan of CDC in prod. Streaming data movement is generally prone to confusion, and it feeds into bad data patterns like hard deletes without any audit logs, no timestamps on updates or deletes, etc. which are usually the reason why batch loads cannot be utilized. They require a decent operational understanding of the underlying database, and have some gotchas like the Erathos folks mentioned in the article. We offer CDC both in our cloud platform, as well our open-source tools, but if I could, I would always pick an incremental batch load with a cursor value over a CDC connection.
I understand it is sometimes required due to organizational complexity or legacy database reasons, mine is just a personal preference.
If anyone is looking for an open-source CDC tool that runs as a standalone Go CLI, check out ingestr: https://github.com/bruin-data/ingestr
What's the benefit vs. something like Postgres's logical replication for CDC? IMO, the hard part of CDC is maintaining consistency in the face of potential network issues or downstream slowdowns. One is forced to choose between scylla: generate excess trx logs if replication slows, and charybdis: lose consistency. I don't see how an open transaction helps here?
1) CDC for archiving/recovery or as an audit log
2) downstream consumers consuming a business-events table. Kind of like inverted event-sourcing pattern.
CDC is sound for sure but only in the lowest technically sense. Downstream consumers consuming business events gets you all the benefits of event sourcing(Namabilty, Replayability etc) while keeping relational guarantees and transactional safety.
Frankly, I am not a big fan of streaming either. But CDC and streaming are two different things. Streaming database replication is generally built on CDC, but you can use CDC with micro-batches too (which is what we do). I wrote about this in another article: https://www.erathos.com/en/blog/cursor-based-sync-vs-change-...
Imo, the key reason for offering CDC is that most databases aren't designed around "how can we extract data efficiently", therefore they often lack a reliable "updated_at" column for us to use as a cursor.
I assume not everyone using MySQL and BigQuery are using CloudSQL and so don’t have Datastream available to them.
Datastream solves the issues mentioned in the article, because it relies on CDC, which is the same solution the article is proposing.
Note that the article seems to have a major error in its first sentence: “MySQL CDC syncs miss deletes and intermediate updates.” CDC is a solution to that issue, it doesn’t suffer from it. The second paragraph correctly describes the approach that has limitations: “a scheduled job selects rows…”