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Subject: BUG #19616: pgoutput sends stream abort ('A') to clients that did not
 enable streaming
To: pgsql-bugs@lists.postgresql.org
From: PG Bug reporting form <noreply@postgresql.org>
Cc: tyler@smarts.io
Reply-To: tyler@smarts.io, pgsql-bugs@lists.postgresql.org
Date: Tue, 11 Aug 2026 22:58:04 +0000
Message-ID: <19616-f6153af509910853@postgresql.org>
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 <https://www.postgresql.org/message-id/19616-f6153af509910853%40postgresql.org>
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The following bug has been logged on the website:

Bug reference:      19616
Logged by:          Tyler Smart
Email address:      tyler@smarts.io
PostgreSQL version: 18.4
Operating system:   Linux (Docker; also Google Cloud SQL)
Description:       =20

Since PostgreSQL 18, pgoutput can send a Stream Abort ('A') message to a
client that connected with proto_version 1 and never enabled streaming.
Protocol 1 clients do not implement the stream message set, so consumers
fail on it: Debezium (and tools that embed it, like Airbyte) dies with
"Unsupported message type: A", and because the crash repeats at the same WAL
position on every restart, the slot stops advancing until
max_slot_wal_keep_size invalidates it.

I reproduced this on 18.4 (Debian 18.4-1.pgdg13+1, official Docker image)
and on Cloud SQL 18.1. The identical script does not reproduce it on 17.10.

The trigger needs three conditions in one decode run:

1. logical_decoding_work_mem is exceeded, so eviction runs.
2. The eviction candidate has already aborted in clog.
3. That transaction has a subtransaction with changes still in memory.