Re: SELECT INTO large FKyed table is slow

On 12/01/2010 01:51 AM, Pierre C wrote:
>
>> Now I tried removing the constraints from the history table (including
>> the PK) and the inserts were fast. After few 'rounds' of inserts I
>> added constraints back, and several round after that were fast again.
>> But then all the same. Insert of some 11k rows took 4 seconds (with
>> all constraints) and now the last one of only 4k rows took one minute.
>> I did vacuum after each insert.
>>
>>
>> Mario
>
> Hm, so for each line of drones_history you insert, you also update the
> correspoding drones table to reflect the latest data, right ?

Yes.

> How many times is the same row in "drones" updated ? ie, if you insert N
> rows in drones_nistory, how may drone_id's do you have ?

Just once.

If I have 5000 lines in CSV file (that I load into 'temporary' table
using COPY) i can be sure that drone_id there is PK. That is because CSV
file contains measurements from all the drones, one measurement per
drone. I usualy have around 100 new drones, so I insert those to drones
and to drones_history. Then I first insert into drones_history and then
update those rows in drones. Should I try doing the other way around?

Although, I think I'm having some disk-related problems because when
inserting to the tables my IO troughput is pretty low. For instance,
when I drop constraints and then recreate them that takes around 15-30
seconds (on a 25M rows table) - disk io is steady, around 60 MB/s in
read and write.

It just could be that the ext3 partition is so fragmented. I'll try
later this week on a new set of disks and ext4 filesystem to see how it
goes.

Mario