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[36.14.41.111]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-842269d68c5sm9492983b3a.27.2026.06.01.22.29.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 01 Jun 2026 22:29:19 -0700 (PDT) Date: Tue, 02 Jun 2026 14:29:18 +0900 (JST) Message-Id: <20260602.142918.705919985422427526.horikyota.ntt@gmail.com> To: mats.kindahl@gmail.com Cc: japinli@hotmail.com, suryapoondla4@gmail.com, pgsql-hackers@lists.postgresql.org Subject: Re: pg_rewind does not rewind diverging timelines From: Kyotaro Horiguchi In-Reply-To: References: <20260601.153058.2271004477925758292.horikyota.ntt@gmail.com> User-Agent: Mew version 6.8 on Emacs 29.4 Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit List-Id: List-Help: List-Subscribe: List-Post: List-Owner: List-Archive: Archived-At: Precedence: bulk At Tue, 2 Jun 2026 04:13:45 +0200, Mats Kindahl wrote in > If two servers go through the same sequence, e.g., start at the same > timeline, does a promote, and write same length but different data > (e.g., add a line to a table, but with different contents), they might > end up with same TLI, same LSN, but different pg_promote calls, and > different database contents, hence it is not possible to distinguish > them. Thanks for the explanation. When I described UUIDs as somewhat heavyweight, I was thinking less about the runtime overhead and more about operational convenience for humans. Your clarification that the UUID only lives in the timeline history file addresses most of the implementation concerns I had in mind. My earlier suggestion was based on the assumption that two independent histories ending up with the same TLI and switchpoint LSN would be rare enough to be ignored in practice. If the goal is to rule out that possibility entirely rather than merely make it extremely unlikely, then I can see why some additional identifier would be needed. In that context, a UUID certainly seems like a viable option. Regards. -- Kyotaro Horiguchi NTT Open Source Software Center