Re: Sorting performance vs. MySQL

On Mon, Feb 22, 2010 at 1:30 PM, Richard Broersma
<richard.broersma@gmail.com> wrote:
> On Mon, Feb 22, 2010 at 10:17 AM, Frank Heikens <frankheikens@mac.com> wrote:
>
>> There is no index on the column transactionid in your PostgreSQL-table, as
>> there is in your MySQL-table. This explains the difference.
>>
>> CREATE INDEX i_transactionid ON public.metarelcloud_transactionlog
>> (transactionid);
>
> Does an index help a sort operation in PostgreSQL?

I also share the same doubt. An external merge-sort needs to make
complete passes over the entire dataset, with no index-directed
accesses.
--
Yang Zhang
http://www.mit.edu/~y_z/