Re: Improving performance of select query

[Thomas Kellerer <shammat@xxxxxxx>]

Karthik Shivashankar schrieb am 14.12.2020 um 12:38:
> I have a postgres(v9.5) table named customer holding 1 billion rows.
> It is not partitioned but it has an index against the primary key
> (integer). I need to keep a very few records (say, about 10k rows)
> and remove everything else.
>
> /insert into customer_backup select * from customer where customer_id in (<id1>,<id2>,..); /
>
>  
>
> If I go for something like above I'm afraid the insert-select may take a very long time as when I ran
>
> /select count(*) from customer;/
>
> it is taking about 45 minutes to return the count.

Well, you need to compare the time with the same condition you use in your
CREATE TABLE .. AS SELECT statement,

e.g.:

   select count(*)
   from customer
   where id in (....);

Or:

   explain (analyze)
   select *
   from customer
   where id in (....);


Regards
Thomas