Re: [WIP] Pipelined Recovery - Mailing list pgsql-hackers

(resending the mail, previous mail was held for moderation for some reason. Now pdf is moved to the tar.gz)

Hi 

I am attaching a new rebased version of the patch. Following are some major changes in the new patch set.

* Streaming replication is now working. The prefetcher was not fully decoupled from the startup process; that's why there were inconsistencies in some scenarios and most of the recovery tap tests were failing. 

* Patch is now split into consumer and producer patches. This will make review easier. 

* Pipeline shutdown flow is also improved. Now producer will always check for the shutdown flag (being set by the consumer)

* Pipeline msg queue size is now configurable `wal_pipeline_queue_size`

* Tap tests now passes with PG_TEST_INITDB_EXTRA_OPTS="-c wal_pipeline=on"

* New tap test for `recovery/t/053_walpipeline.pl`. This covers some basic functionality of the pipeline.

* The filename is changed to xlogpipeline.{h|C}

Thanks to all for the valuable feedback.

Looking forward to your reviews, comments, etc.

--
Regards,
Imran Zaheer

On Wed, Mar 18, 2026 at 12:43 PM Imran Zaheer <imran.zhir@gmail.com> wrote:

Hi Zsolt.

Thanks alot for the review and pointing out the bugs. I have fixed the bugs you mentioned in my new patch set. But
patchset mail is held for moderation for some reason.

>
>   if (reachedRecoveryTarget)
>   {
> + if (wal_pipeline_enabled)
> + WalPipeline_Stop();
>
> What if we didn't reach the recovery target, shouldn't we stop the
> pipelines then?
>

I have fixed the bugs shutdown logic.

As we already know we will exist the recovery redo loop in `PerformWalRecovery()` only in two cases

1: Recovery target reached:

In this case consumers will call to stop the pipeline.

@@ -1807,6 +1931,9 @@ PerformWalRecovery(void)
 
  if (reachedRecoveryTarget)
  {
+ if (wal_pipeline_enabled)
+ WalPipeline_Stop();
+

2: Available pg_wal is consumed and now more wal to read.

In this case pipeline producers will send the shutdown msg to the consumer. Consumer will

detect this message and then call ` WalPipeline_Stop`. This is the case where we cannot read

more records and the while loop will break here.

+ if (decoded_record)
+ {
+ record = &decoded_record->header;
+ return record;
+ }
+ else
+ {
+ /*
+ * We will end up here only when pipeline couldn't read more
+ * records and have sent a shutdown msg. We will acknowldge this
+ * and will trigger request to stop the pipeline workers.
+ */
+ WalPipeline_Stop();
+ return NULL;
+ }

Hope this makes sense. 

Once again thanks for reporting the bugs. You will receive the new patchset mail soon once it is cleared from

the moderation.

Looking forward to your reviews, comments, etc.

Regards,
Imran Zaheer