Are start() methods of batches guaranteed to run sequentially?

Question

The question is very similiar to this one: Are batch jobs guaranteed to run sequentially?

I basically want to ask the same thing, except this time for start() method.

Do start() methods of different batches run sequentially or can start methods of batches run in parallel?

Answer 1

They are guaranteed to run sequentially. This is mentioned in the Execution Governors and Limits documentation:

Maximum number of batch Apex job start method concurrent executions⁴ 1

...

⁴Batch jobs that haven’t started yet remain in the queue until they’re started. If more than one job is running, this limit doesn’t cause any batch job to fail and execute methods of batch Apex jobs still run in parallel.