You could add it to here -- note that if we decide it isn't worth it it'll
just get removed.
Which category would you recommend? Optimizer / Executor?
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Gregory Stark [EMAIL PROTECTED] writes:
But I can also see Tom's reluctance. It's a fair increase in the amount of
code to maintain in that file for a pretty narrow use case. On the other hand
it looks like it would be all in that file. The planner wouldn't have to do
anything special to set
On Thursday 04 December 2008 15:09, Gregory Stark wrote:
tmp [EMAIL PROTECTED] writes:
Also, it is my impression that many people use LIMIT to minimize the
evaluation time of sub queries from which the outer query only needs a
small subset of the sub query output.
I've seen lots of
On 2008-12-06, at 11:29, David Lee Lambert wrote:
I use ORDER BY random() LIMIT :some_small_number frequently to get
a feel
for data. That always builds the unrandomized relation and then
sorts it. I
guess an alternate path for single-table queries would be to
randomly choose
a block
It's slow because there's no way around running through the entire
input. The optimization tmp is talking about wouldn't be relevant
becase there is an order by clause which was precisely why I I said it
was a fairly narrow use case. Most people who use limit want a
specific subset even if
I would tend to think it's worth it myself.
I am unfortunately not familiar enough with the postgresql code base to
be comfortable to provide a patch. Can I submit this optimization
request to some sort of issue tracker or what should I do?
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tmp [EMAIL PROTECTED] writes:
I would tend to think it's worth it myself.
I am unfortunately not familiar enough with the postgresql code base to be
comfortable to provide a patch. Can I submit this optimization request to some
sort of issue tracker or what should I do?
You could add it to
As far as I have understood the following query
SELECT DISTINCT foo
FROM bar
LIMIT baz
is done by first sorting the input and then traversing the sorted data,
ensuring uniqueness of output and stopping when the LIMIT threshold is
reached. Furthermore, a part of the sort procedure is to
tmp [EMAIL PROTECTED] writes:
If the input is sufficiently large and the LIMIT threshold sufficiently
small, maintain the DISTINCT output by hashning while traversing the input and
stop when the LIMIT threshold is reached. No sorting required and *at* *most*
one read of input.
You mean
Gregory Stark wrote:
tmp [EMAIL PROTECTED] writes:
If the input is sufficiently large and the LIMIT threshold sufficiently
small, maintain the DISTINCT output by hashning while traversing the input and
stop when the LIMIT threshold is reached. No sorting required and *at* *most*
one read of
Heikki Linnakangas [EMAIL PROTECTED] writes:
Gregory Stark wrote:
Does that know to stop scanning as soon as it has seen 5 distinct values?
Uhm, hm. Apparently not :(
postgres=# create or replace function v(integer) returns integer as $$begin
raise notice 'called %', $1; return $1; end$$
Heikki Linnakangas [EMAIL PROTECTED] writes:
Gregory Stark wrote:
You mean like this?
postgres=# explain select distinct x from i limit 5;
QUERY PLAN
---
Limit (cost=54.50..54.51 rows=1
In principle, if there are no aggregate functions, then nodeAgg could
return a row immediately upon making any new entry into the hash table.
Whether it's worth the code uglification is debatable ... I think it
would require a third major pathway through nodeAgg.
Regarding whether it's worth
tmp [EMAIL PROTECTED] writes:
Regarding whether it's worth the effort: In each of my three past jobs (all
using postgresql) I have met several queries that would fetch a small subset
of
a large - even huge - input. I think that types of queries are relatively
common out there, but if they
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