Re: contrib idea - Mailing list pgsql-hackers

Tom Lane wrote:
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> >> If you have a foreign key on a column, then whenever the primary key is
> >> modified, the following checks may occur:
> >>
> >> * Check to see if the child row exists (no action)
> >> * Delete the child row (cascade delete)
> >> * Update the child row (cascade update)
> >>
> >> All of which will benefit from an index...
>
> > OK, then perhaps we should be creating an index automatically?  Folks?
>
> We should not *force* people to have an index.  If the master table very
> seldom changes, then an index on the referencing table will be a net
> loss (at least as far as the foreign-key ops go).  You'll pay for it on
> every referencing-table update, and use it only seldom.
>
> Possibly there should be an entry in the "performance tips" chapter
> recommending that people consider adding an index on the referencing
> column if they are concerned about the speed of updates to the
> referenced table.  But I dislike software that considers itself smarter
> than the DBA.

OK, I have added the following to the create_lang.sgml manual page.  I
couldn't find a good place to put this in the performance page.

--
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026
Index: doc/src/sgml/ref/create_table.sgml
===================================================================
RCS file: /cvsroot/pgsql/doc/src/sgml/ref/create_table.sgml,v
retrieving revision 1.50
diff -c -r1.50 create_table.sgml
*** doc/src/sgml/ref/create_table.sgml    2001/12/08 03:24:35    1.50
--- doc/src/sgml/ref/create_table.sgml    2002/01/03 06:23:36
***************
*** 437,442 ****
--- 437,449 ----
         </varlistentry>
        </variablelist>
       </para>
+      <para>
+       If primary key column is updated frequently, it may be wise to
+       add an index to the <literal>REFERENCES</literal> column so that
+       <literal>NO ACTION</literal> and <literal>CASCADE</literal>
+       actions associated with the <literal>REFERENCES</literal>
+       column can be more efficiently performed.
+      </para>

      </listitem>
     </varlistentry>
***************
*** 472,477 ****
--- 479,486 ----
      </listitem>
     </varlistentry>
    </variablelist>
+
+
   </refsect1>