Just thought I would share some rough numbers here.
A bit of an unusual edge case but a big time difference...
A guy using RealBasic (GUI development IDE) which uses sqlite as it's
inbuilt db engine wanted to generate a series of unique codes and
decided sql will help (wanting 30 million codes starts to rule out ram
based solutions)
This is a 7 character alphanumeric code.
His program generated 30M codes in about 15 minutes into the sqlite db
file without any duplicate checks.
Select distinct(pincode) from codes; returned the results (that is to
his client not out to file) after 22 hours and he was after a faster
solution.
Using a unique index to check as he went, inserts dropped from 18,000
per second to about 200 a second after 8 hours (without completing)
(the following times are taken from psql's timing option)
With a P4 3Ghz - 80GB IDE drive - running XP pro - pg 8.2.6 -
Using postgresql (with psql not Realbasic) I created the table and
inserted 30M codes in 5.9 mins
select count(distinct(pincode)) from codes; took about 7.2 minutes
(29,993,182 unique codes of the 30M created)
setting output to a text file - select distinct(pincode) from codes took
18.45 minutes to send them all out (283MB file).
The same hardware running FreeBSD 7.0RC1 GENERIC Kernel -
create the table and insert 30M codes in 5.6 mins
select count(distinct(pincode)) from codes; took 5.9 minutes
(29,993,279 unique codes of the 30M created)
setting output to a text file - select distinct(pincode) from codes took
9.7 minutes to send them all out to file.
It would appear that the method of locating distinct results is the key
here - postgresql sorts the distinct column allowing it to identify a
duplicate or new value quicker - sqlite returns the distinct columns in
the order they are inserted - so it must be scanning all previous
entries in the output to ensure distinct.
--
Shane Ambler
pgSQL (at) Sheeky (dot) Biz
Get Sheeky @ http://Sheeky.Biz