On Wed, 25 Nov 2009, Robert Haas wrote:
On Wed, Nov 25, 2009 at 5:54 PM, Faheem Mitha <faheem@xxxxxxxxxxxxx> wrote:
Well, any method of DISTINCT-ifying is likely to be somewhat slow, but
I've had good luck with SELECT DISTINCT ON (...) in the past, as
compared with other methods. YMMV - the only way to find out is to
benchmark it. I don't think it's non-deterministic if you order by
the DISTINCT-ON columns and enough extras to break any ties - you
should get the first one of each set.
Right, but adding enough extras to break ties is up to the user, and the
language doesn't guarantee anything, so it feels more fragile.
If not, you might want to look at some way of pre-marking the
non-duplicate rows so that you don't have to recompute that each time.
What are the options re pre-marking?
Well, what I usually do is - if I'm going to do the same
distinct-ification frequently, I add an extra column (say, a boolean)
and set it to true for all and only those rows which will pass the
distinct-ification filter. Then I can just say WHERE <that column
name>.
Yes, I see. The problem with is premarking is that the selection is
somewhat dynamic, in the sense that this depends on the idlink table,
which depends on patient data, which can change.
Then you might be able to use the underlying table directly in the next
CTE, which will usually permit better optimization, more use of indices,
etc. It seems pretty unfortunate that dedup_patient_anno joins against geno
and then patient_geno does what appears to be the same join again. Is there
some way to eliminate that? If so it will probably help.
You don't say whether you are looking at the PED or TPED query, so I'll
assume PED. They are similar anyway.
I see your point re the joins. You mean
anno INNER JOIN geno
followed by
geno INNER JOIN dedup_patient_anno
? I think the point of the first join is to reduce the anno table based on
information from the geno table. The result is basically a subset of the
anno table with some potential duplication removed, which is then re-joined
to the geno table. I agree this seems a bit suboptimal, and there might be a
better way to do this.
Yeah, I didn't think about it in detail, but it looks like it should
be possible. Eliminating joins can sometimes have *dramatic* effects
on query performance, and it never hurts.
Failing all else, couldn't I smoosh together the two queries and do a
triple join? For reference, the two CTEs in question, from the PED query,
are as follows.
dedup_patient_anno AS
( SELECT *
FROM
(SELECT *,
row_number() OVER(PARTITION BY anno.rsid ORDER BY
anno.id)
FROM anno
INNER JOIN geno
ON anno.id = geno.anno_id
WHERE idlink_id =
(SELECT MIN(id)
FROM idlink
)
) AS s
WHERE row_number = '1'
),
patient_geno AS
( SELECT geno.idlink_id AS idlink_id,
geno.anno_id AS anno_id,
geno.snpval_id AS snpval_id,
allelea_id, alleleb_id
FROM geno
INNER JOIN dedup_patient_anno
ON geno.anno_id = dedup_patient_anno.id
),
Regards, Faheem.
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