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When UPDATE a row in a table with BEFORE ROW UPDATE trigger, the XMAX of new tuple is set to current XID - Mailing list pgsql-general

From Charles Qi
Subject When UPDATE a row in a table with BEFORE ROW UPDATE trigger, the XMAX of new tuple is set to current XID
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Msg-id CAEawgcJN2V0MTzZu5gi=csNapnJzogxJJqUFSphu6r=OXjorng@mail.gmail.com
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Responses Re: When UPDATE a row in a table with BEFORE ROW UPDATE trigger, the XMAX of new tuple is set to current XID
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And if we do the updates in multiple subtransactions, multixact will be created, which is not created when the BEFORE ROW UPDATE trigger is absent.

Is this behavior by design? If so, what is the purpose for the behavior?

Tested version:
PostgreSQL 14.18 (Ubuntu 14.18-0ubuntu0.22.04.1) on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0, 64-bit

The attached file reproduce.sql can be used to reproduce the behavior. 
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