Tom Lane wrote on 17.07.2010 16:36:
Thomas Kellerer<spam_eater@xxxxxxx> writes:
I'm till a bit surprised that parsing the statement _with_ a column list is mesurably slower than withou a column list.
Well, nobody's offered any actual *numbers* here. It's clear that
parsing the column list will take more time than not doing so, but
whether that adds up to anything significant or even measurable
compared to the rest of the statement's cost is not so clear.
Want to do some experiments?
OK, I wrote a small Java program that inserts rows using a column list and without column list
I did that for 5,10,15 and 20 (integer) columns. then inserting 10000 rows into the empty table.
I measured the runtime as seen from the JDBC client and as reported by explain analyze (the last line reading "Total runtime:")
All times are milliseconds and are averaged over 20 runs
ColumnCount with columns without columns
5 1132 1092.6
10 1288.53 1148.33
15 1430 1215.67
20 1657.6 1313.2
Apparently there *is* a substiantial overhead, but I suspected the sending of the raw SQL literal to be a major factor here.
(Server and JDBC program were running on the same machine)
So I ran "EXECUTE ANALYZE" instead of INSERT to get the processing time of the server and remove the JDBC/SQL literal overhead.
ColumnCount with columns without columns
5 116.33 115.3
10 149.89 128.28
15 169.94 159.14
20 197.72 193.66
Which still shows an overhead, but less.
So apparently the "even slower" in the manual *is* right, as the overhead of sending the longer SQL Statement over the network does impact psql as well.
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