A SpringBatch job to produce events for a PubSub preserving source order

Question

I'm considering to create a SpringBatch job that uses rows from a table to create events and push the events to a PubSub implementation. The problem here is that the order of events should be the same as the order of the rows in the table that used as source for the events creation process.

It seems to me now that the SpringBatch is not designed for such order perseverance, as batches are processed and then written in parallel. The only ugly but probably working solution for this problem would be to do all the processing in the reader (so the reader could do reading+processing+writing to PubSub), that could help to keep order inside paginated batches, but even that doesn't seem to guarantee the batches order, according to the doc

Any ideas how the transition ordered rows->ordered events could be implemented using SpringBatch or, at least, SpringBoot? Thank you in advance!

Answer 1

It seems to me now that the SpringBatch is not designed for such order perseverance, as batches are processed and then written in parallel.

This is true only for a multi-threaded or a partitioned step. The default (single-threaded) chunk-oriented step implementation processes items in the same order returned by the item reader. So if you make your database reader return items in the order you want, those items will be written to your Pub/Sub broker in the same order.