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 - Mailing list pgsql-bugs

From Thadeus Anand
Subject 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
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Msg-id CANUywMG7mrjsLW7-KgC_bi4bPNNojumToT_KL1DN=_7EZe26pg@mail.gmail.com
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In response to RE: [CAUTION: SUSPECT SENDER] RE: [CAUTION: SUSPECT SENDER] RE: BUG #19029: Replication Slot size keeps increasing while logical subscription works fine  ("Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>)
List pgsql-bugs
Thank you Hayato. 

I will check this out today. I'm glad this isn't a bug, but an issue that I can address myself. We can't afford to put the brakes on logical replication for another three months. 

Thadeus Anand. 




On Wed, 27 Aug, 2025, 9:02 am Hayato Kuroda (Fujitsu), <kuroda.hayato@fujitsu.com> wrote:
Dear Thadeus,

Thanks for sharing the info. From your screenshot, I can see that there is a
transaction 10861356 which modifies many tuples. Logical decoding has a mechanism
to spill a part of changes to the disk to avoid using much amount of memory and
it seems to be used here.

I think as next step we can clarify which process starts the transaction.  Can
you run below query when you reproduce the issue?

```
# SELECT * FROM pg_stat_activity WHERE backend_xid = '${XID}';
```

Files under pg_replslot/${slot_name} has a format: `xid-${XID}-lsn-${LSN_UPPER}-${LSN_LOWER}.spill`
so that ${XID} can be tuned when it happns. In your attached case, 10861356.

Best regards,
Hayato Kuroda
FUJITSU LIMITED

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