Re: Perform streaming logical transactions by background workers and parallel apply
Amit Kapila <amit.kapila16@gmail.com>
On Fri, Nov 4, 2022 at 1:36 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Thu, Nov 3, 2022 at 6:36 PM houzj.fnst@fujitsu.com
> <houzj.fnst@fujitsu.com> wrote:
> >
> > Thanks for the analysis and summary !
> >
> > I tried to implement the above idea and here is the patch set.
> >
>
> Few comments on v42-0001
> ===========================
>
Few more comments on v42-0001
===============================
1. In parallel_apply_send_data(), it seems winfo->serialize_changes
and switching_to_serialize are set to indicate that we have changed
parallel to serialize mode. Isn't using just the
switching_to_serialize sufficient? Also, it would be better to name
switching_to_serialize as parallel_to_serialize or something like
that.
2. In parallel_apply_send_data(), the patch has already initialized
the fileset, and then again in apply_handle_stream_start(), it will do
the same if we fail while sending stream_start message to the parallel
worker. It seems we don't need to initialize fileset again for
TRANS_LEADER_PARTIAL_SERIALIZE state in apply_handle_stream_start()
unless I am missing something.
3.
apply_handle_stream_start(StringInfo s)
{
...
+ if (!first_segment)
+ {
+ /*
+ * Unlock the shared object lock so that parallel apply worker
+ * can continue to receive and apply changes.
+ */
+ parallel_apply_unlock(winfo->shared->stream_lock_id);
...
}
Can we have an assert before this unlock call that the lock must be
held? Similarly, if there are other places then we can have assert
there as well.
4. It is not very clear to me how maintaining ParallelApplyLockids
list is helpful.
5.
/*
+ * Handle STREAM START message when the transaction was spilled to disk.
+ *
+ * Inintialize fileset if not yet and open the file.
+ */
+void
+serialize_stream_start(TransactionId xid, bool first_segment)
+{
+ /*
+ * Start a transaction on stream start,
This function's name and comments seem to indicate that it is to
handle stream_start message. Is that really the case? It is being
called from parallel_apply_send_data() which made me think it can be
used from other places as well.
--
With Regards,
Amit Kapila.
Commits
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the thread's linked commits as JSON, with link sources.
API reference →
-
Fix invalid memory access during the shutdown of the parallel apply worker.
- 3d144c6c8602 16.0 landed
-
Fix assertion failure in apply worker.
- de63f8dadee4 16.0 landed
-
Use elog to report unexpected action in handle_streamed_transaction().
- 781ac42d43ab 16.0 landed
-
Use appropriate wait event when sending data in the apply worker.
- d9d7fe68d35e 16.0 landed
-
Allow the logical_replication_mode to be used on the subscriber.
- 9f2213a7c575 16.0 landed
-
Rename GUC logical_decoding_mode to logical_replication_mode.
- 1e8b61735cfb 16.0 landed
-
Display the leader apply worker's PID for parallel apply workers.
- d540a02a724b 16.0 landed
-
Improve the code to decide and process the apply action.
- c981d9145dea 16.0 landed
-
Document the newly added wait events added by commit 216a784829.
- cd06ccd78fcf 16.0 landed
-
Perform apply of large transactions by parallel workers.
- 216a784829c2 16.0 landed
-
Wake up a subscription's replication worker processes after DDL.
- c6e1f62e2cee 16.0 cited
-
Add copyright notices to meson files
- 8284cf5f746f 16.0 cited
-
Better document logical replication parameters
- a8500750ca0a 16.0 cited
-
Add a common function to generate the origin name.
- 776e1c8a5d14 16.0 cited
-
Harmonize parameter names in storage and AM code.
- bfcf1b34805f 16.0 cited
-
Avoid using list_length() to test for empty list.
- efd0c16becbf 16.0 cited
-
Improve two comments related to a boolean DefElem's value
- 8445f5a21d40 16.0 cited
-
Fix partition table's REPLICA IDENTITY checking on the subscriber.
- 26b3455afaa9 15.0 cited
-
Fix data inconsistency between publisher and subscriber.
- b7658c24c7c1 15.0 cited
-
Fix cache look-up failures while applying changes in logical replication.
- 5a97b1325453 15.0 cited