Re: Stopping logical replication protocol

 

OK, so thinking about this some more, I see why you've added the callback within the reorder buffer code. You want to stop processing of a transaction after we've decoded the commit and are looping over the changes within ReorderBufferCommit(...), which doesn't know anything about the walsender. So we could loop for a long time within WalSndLoop -> XLogSendLogical -> LogicalDecodingProcessRecord if the record is a commit, as we process each change and send it to the client.

So aborting processing and returning between individual changes in ReorderBufferCommit(...) seems very reasonable. I agree that some kind of callback is needed because the walsender uses static globals to control its send/receive stop logic. I don't like the naming "is_active"; maybe reverse the sense and call it "stop_decoding_cb" ? Or "continue_decoding_cb"? Unsure.

Anyway, here's a draft patch that does the parts other than the reorder buffer processing stop. It passes 'make check' and the src/test/recovery tests, but I haven't written anything to verify the client-initiated abort handling. You have test code for this and I'd be interested to see the results.

This patch doesn't attempt to allow decoding to be aborted during processing of an xlog record, including a commit. So it'll still attempt to send whole transactions. But it should allow clients to send CopyDone when we're waiting for new WAL to be generated and return to command mode then.

I think it's worth making the next step, where you allow reorder buffer commit processing to be interrupted, into a separate patch on top of this one. They're two separate changes IMO.