select count(*) from <table> is probably not using the index that your insert/select would, so I would not use that as a test for performance.
If customer_backup has an index, the insert-select will be performance-limited by updating that index.
If you can do a create table customer_backup as select * from customer where customer_id in (<id1>,<id2>,..);
I expect it to run quite fast as long as customer_id is indexed and analyzed.
On Mon, Dec 14, 2020 at 9:37 AM Muhammad Bilal Jamil <mbjamil92@xxxxxxxxx> wrote:
I think you can also increase the query performance by creating indexes?On Mon, 14 Dec 2020 at 11:36, Rob Sargent <robjsargent@xxxxxxxxx> wrote:
> On Dec 14, 2020, at 4:47 AM, Thomas Kellerer <shammat@xxxxxxx> wrote:
>
> 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
>
As for the actually copy of the specific records, I would ‘where exists’ (even possibly with a temp table of ids) rather than in(id1..id10000)
>
