Re: Perform streaming logical transactions by background workers and parallel apply

Dilip Kumar <dilipbalaut@gmail.com>

From: Dilip Kumar <dilipbalaut@gmail.com>

To: "wangw.fnst@fujitsu.com" <wangw.fnst@fujitsu.com>

Cc: Peter Smith <smithpb2250@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, "shiy.fnst@fujitsu.com" <shiy.fnst@fujitsu.com>, "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>

Date: 2022-07-26T09:00:11Z

Lists: pgsql-hackers

On Fri, Jul 22, 2022 at 8:27 AM wangw.fnst@fujitsu.com
<wangw.fnst@fujitsu.com> wrote:
>
> On Tues, Jul 19, 2022 at 10:29 AM I wrote:
> > Attach the news patches.
>
> Not able to apply patches cleanly because the change in HEAD (366283961a).
> Therefore, I rebased the patch based on the changes in HEAD.
>
> Attach the new patches.

+    /* Check the foreign keys. */
+    fkeys = RelationGetFKeyList(entry->localrel);
+    if (fkeys)
+        entry->parallel_apply = PARALLEL_APPLY_UNSAFE;

So if there is a foreign key on any of the tables which are parts of a
subscription then we do not allow changes for that subscription to be
applied in parallel?  I think this is a big limitation because having
foreign key on the table is very normal right?  I agree that if we
allow them then there could be failure due to out of order apply
right? but IMHO we should not put the restriction instead let it fail
if there is ever such conflict.  Because if there is a conflict the
transaction will be sent again.  Do we see that there could be wrong
or inconsistent results if we allow such things to be executed in
parallel.  If not then IMHO just to avoid some corner case failure we
are restricting very normal cases.

-- 
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits 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