Обсуждение: help with design of the 'COUNT(*) in separate table schema

Regarding the previously discussed triggers on tables to keep track of count:
http://www.varlena.com/GeneralBits/120.php
http://www.varlena.com/GeneralBits/49.php
<from article>
CREATE OR REPLACE FUNCTION count_rows()
RETURNS TRIGGER AS
'
   BEGIN
      IF TG_OP = ''INSERT'' THEN
         UPDATE rowcount
            SET total_rows = total_rows + 1
            WHERE table_name = TG_RELNAME;
      ELSIF TG_OP = ''DELETE'' THEN
         UPDATE rowcount
            SET total_rows = total_rows - 1
            WHERE table_name = TG_RELNAME;
      END IF;
      RETURN NULL;
   END;
' LANGUAGE plpgsql;
</from article>

Wouldn't something like this need row-locking (SELECT for UPDATE) in order to serialize the execution of all triggers?

Dennis Gearon

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----------------
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  otherwise we all die.

On 20 October 2010 23:52, Dennis Gearon <gearond@sbcglobal.net> wrote:
> Regarding the previously discussed triggers on tables to keep track of count:
> http://www.varlena.com/GeneralBits/120.php
> http://www.varlena.com/GeneralBits/49.php
> <from article>
> CREATE OR REPLACE FUNCTION count_rows()
> RETURNS TRIGGER AS
> '
>   BEGIN
>      IF TG_OP = ''INSERT'' THEN
>         UPDATE rowcount
>            SET total_rows = total_rows + 1
>            WHERE table_name = TG_RELNAME;
>      ELSIF TG_OP = ''DELETE'' THEN
>         UPDATE rowcount
>            SET total_rows = total_rows - 1
>            WHERE table_name = TG_RELNAME;
>      END IF;
>      RETURN NULL;
>   END;
> ' LANGUAGE plpgsql;
> </from article>
>
> Wouldn't something like this need row-locking (SELECT for UPDATE) in order to serialize the execution of all
triggers?
>

The update will acquire a row level lock on rowcount for the
TG_RELNAME tuple without you doing anything else.

--
Regards,
Peter Geoghegan