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Commit 71f996d2 authored by Andrew Dunstan's avatar Andrew Dunstan
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Explain unaccounted for space in pgstattuple.

In addition to space accounted for by tuple_len, dead_tuple_len and
free_space, the table_len includes page overhead, the item pointers
table and padding bytes.

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......@@ -117,6 +117,16 @@ free_percent | 1.95
</tgroup>
</table>
<note>
<para>
The <literal>table_len</literal> will always be greater than the sum
of the <literal>tuple_len</literal>, <literal>dead_tuple_len</literal>
and <literal>free_space</literal>. The difference is accounted for by
fixed page overhead, the per-page table of pointers to tuples, and
padding to ensure that tuples are correctly aligned.
</para>
</note>
<para>
<function>pgstattuple</function> acquires only a read lock on the
relation. So the results do not reflect an instantaneous snapshot;
......
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