Improving performance of select query

Hi,

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.

Are there ways to improve the efficiency of the insert-select by , say, tuning some configurations related to memory to improve the efficiency ?

This is a box with 96GB of RAM overall and I can stop all the data load and DML operations if needed. But need a way to run this query as much efficiently as possible

Thanks and Regards,
Karthik

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