RE: Slow catchup of 2PC (twophase) transactions on replica in LR

Hayato Kuroda (Fujitsu) <kuroda.hayato@fujitsu.com>

From: "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>

To: 'Peter Smith' <smithpb2250@gmail.com>

Cc: "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>, Amit Kapila <amit.kapila16@gmail.com>, Ajin Cherian <itsajin@gmail.com>, Давыдов Виталий <v.davydov@postgrespro.ru>

Date: 2024-05-09T08:26:19Z

Lists: pgsql-hackers

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Fix random failure in 021_twophase.
- 0dcea330babd 18.0 landed
Allow altering of two_phase option of a SUBSCRIPTION.
- 1462aad2e447 18.0 landed
Doc: use true|false rather than on|off for "failover" option
- fa65a022db26 17.0 cited
Support an optional asynchronous commit mode, in which we don't flush WAL
- 4a78cdeb6b59 8.3.0 cited

Dear Peter,

Thanks for reviewing! The patch will be posted in the upcoming post.

> ======
> src/backend/access/transam/twophase.c
> 
> 1. IsTwoPhaseTransactionGidForSubid
> 
> +/*
> + * IsTwoPhaseTransactionGidForSubid
> + * Check whether the given GID is formed by TwoPhaseTransactionGid.
> + */
> +static bool
> +IsTwoPhaseTransactionGidForSubid(Oid subid, char *gid)
> 
> I think the function comment should mention something about 'subid'.
> 
> SUGGESTION
> Check whether the given GID (as formed by TwoPhaseTransactionGid) is
> for the specified 'subid'.

Fixed.

> src/backend/commands/subscriptioncmds.c
> 
> 2. AlterSubscription
> 
> + if (!opts.twophase &&
> + form->subtwophasestate == LOGICALREP_TWOPHASE_STATE_ENABLED
> &&
> + LookupGXactBySubid(subid))
> + /* Add error message */
> + ereport(ERROR,
> + (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
> + errmsg("cannot disable two_phase when uncommitted prepared
> transactions present"),
> + errhint("Resolve these transactions and try again")));
> 
> The comment "/* Add error message */" seems unnecessary.

Yeah, this was an internal flag. Removed.

Best Regards,
Hayato Kuroda
FUJITSU LIMITED
https://www.fujitsu.com/