Re: Parent/child context relation in pg_get_backend_memory_contexts()

> +     <row>
> +      <entry role="catalog_table_entry"><para
> role="column_definition">
> +       <structfield>context_id</structfield> <type>int4</type>
> +      </para>
> +      <para>
> +       Current context id. Note that the context id is a temporary id
> and may
> +       change in each invocation
> +      </para></entry>
> +     </row>
> +
> +     <row>
> +      <entry role="catalog_table_entry"><para
> role="column_definition">
> +       <structfield>path</structfield> <type>int4[]</type>
> +      </para>
> +      <para>
> +       Path to reach the current context from TopMemoryContext.
> Context ids in
> +       this list represents all parents of the current context. This
> can be
> +       used to build the parent and child relation
> +      </para></entry>
> +     </row>
> +
> +     <row>
> +      <entry role="catalog_table_entry"><para
> role="column_definition">
> +       <structfield>total_bytes_including_children</structfield>
> <type>int8</type>
> +      </para>
> +      <para>
> +       Total bytes allocated for this memory context including its
> children
> +      </para></entry>
> +     </row>

These columns are currently added to the bottom of the table, but it may
be better to put semantically similar items close together and change
the insertion position with reference to other system views. For
example,

- In pg_group and pg_user, 'id' is placed on the line following 'name',
so 'context_id' be placed on the line following 'name'
- 'path' is similar with 'parent' and 'level' in that these are
information about the location of the context, 'path' be placed to next
to them.

If we do this, orders of columns in the system view should be the same,
I think.

14dd0f27d have introduced new macro foreach_int.
It seems to be able to make the code a bit simpler and the commit log
says this macro is primarily intended for use in new code. For example: