"Michael Guyver" <kenevel@xxxxxxxxxxxxxx> writes: > CREATE OR REPLACE FUNCTION test_v_01() RETURNS VARCHAR AS $$ > DECLARE > buffer varchar; > i int4; > BEGIN > buffer := 'the quick brown fox jumps over the lazy dog'; > FOR i IN 1..1000 LOOP > buffer := buffer || 'the quick brown fox jumps over the lazy dog'; > END LOOP; > RETURN buffer; > END; > $$ > LANGUAGE plpgsql; I looked into this a bit with gprof/oprofile, and found that there are two issues skewing the results of this test: * the function ought to be declared STABLE or even IMMUTABLE. The fact that it is not creates significant snapshot/command-counter overhead. (This cost is about the same for both variants, though.) * the buffer variable, and probably the function result too, ought to be declared TEXT not VARCHAR. That's because the result of the concat operator is always TEXT, and plpgsql is not bright about the fact that the conversion from text to varchar could be optimized away. There isn't any comparable cost for the array_append approach because of the way that the result type of array_append() is determined --- it comes out varchar[]. After correcting these issues I find that the concat approach is about 20% faster than the array_append approach, which is more in line with what I expected. regards, tom lane
