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From wenhui qiu
Subject Re: Parallel Apply
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Msg-id CAGjGUAKKA=raicKoKU4-sviUp=mEw6B8sLd22H4N-twtWVrY1g@mail.gmail.com
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In response to Re: Parallel Apply  (Tomas Vondra <tomas@vondra.me>)
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Hi Tomas 
> discussing some of this stuff. I'm not saying we should copy all of
> this, but it seems like a good source of inspiration what (not) to do.
I'm not saying we should copy MySQL's implementation. MySQL’s parallel replication is based on group commit, and PostgreSQL can’t directly adopt that approach. However, MySQL hashes transactions within the same commit group by primary and unique keys, assuming that transactions with different hashes do not conflict (since MySQL's row locks are based on index ). This allows transactions to be safely replayed in parallel on replicas, and their execution order within the group doesn’t matter.


Thanks 

On Thu, Nov 20, 2025 at 10:50 PM Tomas Vondra <tomas@vondra.me> wrote:
On 11/20/25 14:10, wenhui qiu wrote:
> Hi 
>> 1) The way the patch determines dependencies seems to be the "writeset"
>> approach from other replication systems (e.g. MySQL does that). Maybe we
>> should stick to the same naming?
>
>> OK, I did not research the design in MySQL in detail but will try to
> analyze it.
> I have some documents  for mysql parallel apply binlog event.But after
> MySQL 8.4, only the writeset mode is available. In scenarios with a
> primary key or unique key, the replica replay is not ordered, but the
> data is eventually consistent."
> https://dev.mysql.com/worklog/task/?id=9556 <https://dev.mysql.com/
> worklog/task/?id=9556>
> https://dev.mysql.com/blog-archive/improving-the-parallel-applier-with-
> writeset-based-dependency-tracking/ <https://dev.mysql.com/blog-archive/
> improving-the-parallel-applier-with-writeset-based-dependency-tracking/>
> https://medium.com/airtable-eng/optimizing-mysql-replication-lag-with-
> parallel-replication-and-writeset-based-dependency-tracking-1fc405cf023c
> <https://medium.com/airtable-eng/optimizing-mysql-replication-lag-with-
> parallel-replication-and-writeset-based-dependency-tracking-1fc405cf023c>
>

FWIW there was a talk about MySQL replication at pgconf.dev 2024

  https://www.youtube.com/watch?v=eOfUqh5PltM

discussing some of this stuff. I'm not saying we should copy all of
this, but it seems like a good source of inspiration what (not) to do.


regards

--
Tomas Vondra

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