Re: insert vs select into performance

Michael Glaesemann wrote:
>
> On Jul 17, 2007, at 14:38 , Thomas Finneid wrote:
>
>> I was doing some testing on "insert" compared to "select into". I
>> inserted 100 000 rows (with 8 column values) into a table, which took
>> 14 seconds, compared to a select into, which took 0.8 seconds.
>> (fyi, the inserts where batched, autocommit was turned off and it all
>> happend on the local machine)
>>
>> Now I am wondering why the select into is that much faster?
>
> It would be helpful if you included the actual queries you're using, as
> there are a number of variables:

create table ciu_data_type
(
id integer,
loc_id integer,
value1 integer,
value2 real,
value3 integer,
value4 real,
value5 real,
value6 char(2),
value7 char(3),
value8 bigint,
value9 bigint,
value10 real,
value11 bigint,
value12 smallint,
value13 double precision,
value14 real,
value15 real,
value16 char(1),
value17 varchar(18),
value18 bigint,
value19 char(4)
);

performed with JDBC

insert into ciu_data_type (id, loc_id, value3, value5, value8, value9,
value10, value11 ) values (?,?,?,?,?,?,?,?)

select * into ciu_data_type_copy from ciu_data_type

> 1) If there are any constraints on the original table, the INSERT will
> be checking those constraints. AIUI, SELECT INTO does not generate any
> table constraints.

No constraints in this test.

> 2a) Are you using INSERT INTO foo (foo1, foo2, foo2) SELECT foo1, foo2,
> foo3 FROM pre_foo or individual inserts for each row? The former would
> be faster than the latter.
>
> 2b) If you are doing individual inserts, are you wrapping them in a
> transaction? The latter would be faster.

disabling autocommit, but nothing more than that

I havent done this test in a stored function yet, nor have I tried it
with a C client so far, so there is the chance that it is java/jdbc that
makes the insert so slow. I'll get to that test soon if there is any
chance my theory makes sence.

regards

thomas