When updating row that has TOAST column, is the TOAST column also reinserted ? Or just the oid to the value?

From: Dorian Hoxha <dorian(dot)hoxha(at)gmail(dot)com>
To: PostgreSql-general <pgsql-general(at)postgresql(dot)org>
Subject: When updating row that has TOAST column, is the TOAST column also reinserted ? Or just the oid to the value?
Date: 2016-12-13 13:09:32
Message-ID: CANsFX07ozgyRx-0kvt_cdFWC0zJHJzifu68sS4xiSW-25DFNdg@mail.gmail.com
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Hello friends,

When updating row that has TOAST column, is the TOAST column also inserted
? Or just the oid?
Say I have a 1MB value in the TOAST column, and I update the row by
changing another column, and since every update is an insert, will it also
reinsert the toast-column ? The column that I will update will have an
index so I think hot-update won't work in this case ? The same question
also when full-page-writes is enabled ?

Using 9.6.

Thank you!

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