From: benj.dev@laposte.net
To: pgsql-docs@lists.postgresql.org
Subject: HeapTupleHeaderData Layout description
Date: Fri, 22 Jan 2021 14:50:45 +0100 (CET)
Message-ID: <658235472.1027001.1611323445204@wlpnf0217> (raw)
<div style="font-family:Arial, Helvetica, sans-serif; font-size:12px;">Hi,<br>
<br>
In https://www.postgresql.org/docs/13/storage-page-layout.html<br;
we can find on § 68.6.1. Table Row Layout<br>
the Table 68.4. HeapTupleHeaderData Layout<br>
<br>
When additionning Length of differents Fields taht are present we obtain atotal of<br>
4+4+4+4+6+2+2+1 = 27<br>
<br>
What doesn't seem to fit with previous indication "There is a fixed-size header (occupying 23 bytes on most machines)"<br>
<br>
Researching in old doc shows that in 8.2 the documentation<br>
https://www.postgresql.org/docs/8.2/storage-page-layout.html<br;
indicate 27 bytes (with the same detailled Table)<br>
<br>
Number 23 appears from Postgres 8.3<br>
<br>
In some thread like https://stackoverflow.com/questions/2966524/calculating-and-saving-space-in-postgresql/7431468<br;
It's possible to read that<br>
Overhead per tuple (row)<br>
... And at least 24 bytes (23 + padding) for the tuple header ...<br>
<br>
As there is several thread about this point I suppose there is an evolution between 8.2 and 8.3 with a missdocumentation for an evolution of detailled Table "HeapTupleHeaderData Layout"<br>
<br>
IS it right ? And in this case what is the real detailled Table ?<br>
<br>
Thanks for any explanations<br>
Regards</div>
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