Why is Cockroach adding READ COMMITTED? Is using a lower level of isolation better for performance or just reduces the amount of serialization errors and retries that need to be done?
READ COMMITTED is great for applications that need a coherent snapshot of the database but not necessarily the absolutely most recent data, which in my experience is actually most apps.
It allows readers to see valid data (relationships are correct), while not blocking writers. It can be the difference between constant deadlocks and super-high throughput without lock contention.
The main motivation is reduce serialization errors, for applications that can handle the weaker isolation level. Especially for applications that were previously running fine under RC on another database.
It allows readers to see valid data (relationships are correct), while not blocking writers. It can be the difference between constant deadlocks and super-high throughput without lock contention.