Bruce Momjian wrote:
> OK, I think I have some more information on this.
> OK, now for some times. On my machine (PP200 running BSD/OS), the
> startup/shutdown time for the database is 0.15 seconds, so I will
> subtract that time to show the incremental elapsed wallclock time for
> each command:
>
> Select without order by: 0.01
>
> Select with order by: 0.30
>
> Create Table: 0.11
> Create Index: 0.54
>
> Insert into Table: 0.01
>
> These are all times on a table with one integer column, and one row.
>
> As you can see, the ORDER BY has slowed the SELECT by a factor of 30.
> You can actually create three tables in the same time, or insert 30
> rows.
>
> This looks like a pretty serious performance problem.
By having a small table, you are really just measuring the overhead in
setting up the sort. Try something with a _lot_ of data, and try to have
the data inserted randomly if possible. Another thing to check is the
fundamental time it takes to actually do sorting (for example, put the
same data into a little test program which calls qsort(), or find the
Knuth algorithm and call that directly). Sorts aren't (usually) cheap!
- Tom
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End of hackers-digest V1 #396
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