Re: Adding TEXT columns tanks performance?

On 2/8/07, Arturo Perez <aperez@hayesinc.com> wrote:
> Hi all,
>
> Saturday I changed a table to add a varchar(24) and a TEXT column.
> It's used for some reporting purposes (small potatoe stuff really)
> and the TEXT column remains mostly empty.  However, this week
> performance has gotten terrible.  Queries joining against the
> aforementioned table have gone from 40s to 1500s.  The schema change
> is the only explanation I have for the 30x slower queries.  The
> queries have definitely gotten disk-bound (I can see the connection
> process sitting in the D state for several minutes).
>
> This is pg8.1.4 on Linux RedHat. Would adding a TEXT column impact
> things that much?  The change to the schema was
>
> alter table foo add column title text;

explain analyze please.

no reason for adding text column to do that.  especially since you
didn't default the column which would effectively update the entire
table.

merlin