Re: [CAUTION: SUSPECT SENDER] RE: [CAUTION: SUSPECT SENDER] RE: [CAUTION: SUSPECT SENDER] RE: BUG #19029: Replication Slot size keeps increasing while logical subscription works fine

Hi Hayato san,

Thank you for your response. Thanks again to your colleagues Amit and
Vignesh as well for spending their valuable time to help.

I have altered all my subscriptions to enable streaming. I just set it on
to begin with, and did not set it to parallel. I will also watch
pg_stat_activity and identify the large transactions that may be causing
the spills.

Will update back if anything worthwhile comes up.

On a completely different note, is there any possibility for you developers
at PostgreSQL to consider making the tables at the subscriber side read
only, so that nobody makes changes to them accidentally? I am asking this
because sometimes when it happens, the logical replication fails, and
making the subscriber tables read only can reduce a lot of headache. Please
consider.

Thadeus Anand.

On Wed, Aug 27, 2025 at 12:51 PM Hayato Kuroda (Fujitsu) <
kuroda(dot)hayato(at)fujitsu(dot)com> wrote:

> Dear Thadeus, Nantha,
>
> > Can these spill files in the pg_replslot folder be deleted safely, if
> all the subscribers have
> > caught up?
>
> Do not remove them manually. Spill files exist because the logical
> replication
> system considers they are needed. I cannot know your system well, but in
> your
> first example, there is a possibility that transaction 10861356 is not
> committed
> yet thus walsender keep decoding and spilling. Actually it looks for me
> that
> subscribers have not been caught up.
> Removing them may cause unexpected behavior.
>
> > (I noticed last night when I restarted my publisher, the spill files
> were removed
> > automatically)
>
> When postmaster restarts, it checks all directory under pg_replslot and
> removes
> all .spill files. This is harmless because spilled changes would be
> decoded again.
>
> > Can I use ALTER SUBSCRIPTION to set streaming on, with my existing
> subscriptions?
>
> Yes, you can. More detail, after you run ALTER SUBSCRIPTION command, the
> apply
> worker on the subscriber restarts and establishes the connection again
> with the
> different streaming parameter.
>
> Note that pg_stat_activity (with the pid) is still needed to understand
> the issue correctly.
>
> Best regards,
> Hayato Kuroda
> FUJITSU LIMITED
>
>