Re: Perform streaming logical transactions by background workers and parallel apply
Amit Kapila <amit.kapila16@gmail.com>
On Fri, Jul 22, 2022 at 8:26 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.
>
Few comments on 0001:
======================
1.
- <structfield>substream</structfield> <type>bool</type>
+ <structfield>substream</structfield> <type>char</type>
</para>
<para>
- If true, the subscription will allow streaming of in-progress
- transactions
+ Controls how to handle the streaming of in-progress transactions:
+ <literal>f</literal> = disallow streaming of in-progress transactions,
+ <literal>t</literal> = spill the changes of in-progress transactions to
+ disk and apply at once after the transaction is committed on the
+ publisher,
+ <literal>p</literal> = apply changes directly using a background worker
Shouldn't the description of 'p' be something like: apply changes
directly using a background worker, if available, otherwise, it
behaves the same as 't'
2.
Note that if an error happens when
+ applying changes in a background worker, the finish LSN of the
+ remote transaction might not be reported in the server log.
Is there any case where finish LSN can be reported when applying via
background worker, if not, then we should use 'won't' instead of
'might not'?
3.
+#define PG_LOGICAL_APPLY_SHM_MAGIC 0x79fb2447 // TODO Consider change
It is better to change this as the same magic number is used by
PG_TEST_SHM_MQ_MAGIC
4.
+ /* Ignore statistics fields that have been updated. */
+ s.cursor += IGNORE_SIZE_IN_MESSAGE;
Can we change the comment to: "Ignore statistics fields that have been
updated by the main apply worker."? Will it be better to name the
define as "SIZE_STATS_MESSAGE"?
5.
+/* Apply Background Worker main loop */
+static void
+LogicalApplyBgwLoop(shm_mq_handle *mqh, volatile ApplyBgworkerShared *shared)
{
...
...
+ apply_dispatch(&s);
+
+ if (ConfigReloadPending)
+ {
+ ConfigReloadPending = false;
+ ProcessConfigFile(PGC_SIGHUP);
+ }
+
+ MemoryContextSwitchTo(oldctx);
+ MemoryContextReset(ApplyMessageContext);
We should not process the config file under ApplyMessageContext. You
should switch context before processing the config file. See other
similar usages in the code.
6.
+/* Apply Background Worker main loop */
+static void
+LogicalApplyBgwLoop(shm_mq_handle *mqh, volatile ApplyBgworkerShared *shared)
{
...
...
+ MemoryContextSwitchTo(oldctx);
+ MemoryContextReset(ApplyMessageContext);
+ }
+
+ MemoryContextSwitchTo(TopMemoryContext);
+ MemoryContextReset(ApplyContext);
...
}
I don't see the need to reset ApplyContext here as we don't do
anything in that context here.
--
With Regards,
Amit Kapila.
Commits
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