(And clearly both optimizations are *really* important for performance -
both in real use cases and also in benchmarks.)
On 4/6/16 8:37 AM, Taewoo Kim wrote:
Hello Magnus,
Right now, the search does not stop until it finds all tuples that
satisfies the given predicate. However, if you have an ORDER BY clause
before LIMIT, it can stop sorting process in ORDER BY early. That is,
it picks top K (in your example, K is 2) and sorting process stops early.
Actually, if the plan qualifies as an index-only plan (the given
predicate can be covered by a secondary index search and you only
return secondary key field and/or primary key field), the LIMIT can be
applied to an index-search so that an index-search can be stopped
earlier after finding K tuples. This feature is already implemented
but in the code-review now. It would be applied soon.
Best,
Taewoo
On Wed, Apr 6, 2016 at 7:22 AM, Magnus Kongshem
<kongs...@online.ntnu.no <mailto:kongs...@online.ntnu.no>> wrote:
Hey,
Performing a query with the limit clause, does this cause the
query to stop searching when it reaches the value of the limit
parameter(like in SQL), or does it keep searching for every
matching object and then return the number of objects specified by
the limit? Example below:
use dataverse XXX;
from $obj in dataset YYY
where $obj.timestamp >= 1412121600
and $obj.timestamp <= 1412726400
limit 2
return $obj;
Followup questions may occur.
--
Mvh
Magnus Alderslyst Kongshem
+47 415 65 906 <tel:%2B47%20415%2065%20906>
