Re: Quick question regarding HeapTupleHeaderData.t_ctid

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Aleksander Alekseev <aleksander(at)timescale(dot)com>
Cc: PostgreSQL Development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Quick question regarding HeapTupleHeaderData.t_ctid
Date: 2022-06-12 15:24:37
Message-ID: 3458675.1655047477@sss.pgh.pa.us
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Aleksander Alekseev <aleksander(at)timescale(dot)com> writes:
> So t_ctid will point to the newer version of the tuple regardless of
> whether HOT is used or not. But I couldn't find an answer to how
> t_ctid is used when a tuple is not a part of a HOT chain, or is the
> last item in the chain.

t_ctid points to the tuple itself if it's the latest version of its row.

> Which brings a question, maybe it shouldn't
> take that much space on disk.

How would you make it optional? In particular, what are you going to
to when it's time to update a row (and therefore insert a ctid link)
and the page is already completely full?

regards, tom lane

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