I'm writing a plpgsql function that effectively does a merge join on the
results of two queries. Now, it appears that I cannot read the results of
two queries as streams in plpgsql, so I need to copy the contents of one
query into an array first, and then iterate over the second query
afterwards.
I have discovered that creating large arrays in plpgql is rather slow. In
fact, it seems to be O(n^2). The following code fragment is incredibly
slow:
genes = '{}';
next_new = 1;
FOR loc IN SELECT location.* FROM location, gene WHERE location.subjectid = gene.id ORDER BY objectid, intermine_start, intermine_end LOOP
genes[next_new] = loc;
IF (next_new % 10000 = 0) THEN
RAISE NOTICE 'Scanned % gene locations', next_new;
END IF;
next_new = next_new + 1;
END LOOP;
genes_size = coalesce(array_upper(genes, 1), 0);
RAISE NOTICE 'Scanned % gene locations', genes_size;
For 200,000 rows it takes 40 minutes.
So, is there a way to dump the results of a query into an array quickly in
plpgsql, or alternatively is there a way to read two results streams
simultaneously?
Matthew
--
I would like to think that in this day and age people would know better than
to open executables in an e-mail. I'd also like to be able to flap my arms
and fly to the moon. -- Tim Mullen
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