Re: update problem?

Hi,

I'm working with Juergen at the same Problem.

Consider the following table:

> create table test (a char);

Now fill the table with some data from test.txt
(100.000 rows each row one character)

> \copy test from test.txt

Now update the table

> update test set a='x';

This takes nearly 3 seconds. That would be ok for us.
But adding a column and fill it with some data

> alter table test add b text;
> update test set b='foobar...foobar...foobar... ...';

now the update

> update test set a='y';

takes 8 seconds. When I add further columns or increase
the amount of data a column holds it gets even worse.

Before the column was added explain said:

> explain update test set a='x';
> Seq Scan on test2 (cost=0.00..20.00 rows=1000 width=6)

(btw: why rows=1000? there are 100.000 rows in the table)

And after it was added:

> explain update test set a='y';
> Seq Scan on test2 (cost=0.00..20.00 rows=1000 width=38)

And for our "real world" table (plain table, no foreign keys) it says:

> explain update karte_archiv set ar_k_rechmod='2';
> Seq Scan on karte_archiv (cost=0.00..1609.99 rows=45399 width=359)

This update takes over 30 seconds!
It uses 7 or 8 logfiles in the pg_xlog directory 16MB each.
But does this explain why it take *so* long?

Jörg