On Thu, Sep 23, 2010 at 12:53, Erik Huelsmann <ehuels_at_gmail.com> wrote:
> On Wed, Sep 22, 2010 at 11:25 PM, Greg Stein <gstein_at_gmail.com> wrote:
>> Wouldn't it be better to do:
>> where wc_id = ?1 and local_relpath = ?2
>> and op_depth = (select max(op_depth) from nodes
>> where wc_id=?1 and local_relpath=?2 and op_depth > 0);
>> It seems that eliminating the "order by" and "limit", in favor of
>> max() will tell sqlite what we're really searching for: the maximal
> I wrote those queries like that because Bert said it would introduce an
> aggregation function - at the time he said it, that sounded like it was
> something negative.
I don't think we should be second-guessing the sqlite query optimizer
unless and until we need to. The 'select max(op_depth)' query can be
optimized. If sqlite does not, then that is not our problem until some
performance data shows these queries are killing us.
>> > @@ -312,7 +312,7 @@ WHERE wc_id = ?1 AND local_relpath = ?2;
>> > update nodes set translated_size = ?3, last_mod_time = ?4
>> > where wc_id = ?1 and local_relpath = ?2
>> > and op_depth = (select op_depth from nodes
>> > - where wc_id = ?1 and local_relpath = ?2
>> > + where wc_id = ?1 and local_relpath = ?2 and op_depth
>> > > 0
>> > order by op_depth desc
>> > limit 1);
>> This one does not. The rest of the statements you converted all use
>> the "in" variant.
> The "in" variant is probably better, because - especially with the op_depth
>> 0 restriction - the result set can probably be empty.
Excellent point! Thanks.
Received on 2010-09-23 19:04:43 CEST