Re: Postgres insert performance and storage requirement compared to Oracle

On 10/26/2010 5:27 PM, Jon Nelson wrote:
> start loop:
> populate rows in temporary table
> insert from temporary table into permanent table
> truncate temporary table
> loop
>
> I do something similar, where I COPY data to a temporary table, do
> lots of manipulations, and then perform a series of INSERTS from the
> temporary table into a permanent table.
>

1) It's definitely not faster because you have to insert into the
temporary table, in addition to inserting into the permanent table.
2) This is what I had in mind:

mgogala=# create table a(c1 int);
CREATE TABLE
mgogala=# create temporary table t1(c1 int) on commit delete rows;
CREATE TABLE
mgogala=# begin;
BEGIN
mgogala=# insert into t1 select generate_series(1,1000);
INSERT 0 1000
mgogala=# insert into a select * from t1;
INSERT 0 1000
mgogala=# commit;
COMMIT
mgogala=# select count(*) from a;
count
-------
1000
(1 row)

mgogala=# select count(*) from t1;
count
-------
0
(1 row)

The table is created with "on commit obliterate rows" option which means
that there is no need to do "truncate". The "truncate" command is a
heavy artillery. Truncating a temporary table is like shooting ducks in
a duck pond, with a howitzer.

--

Mladen Gogala
Sr. Oracle DBA
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