Fetching Millions Records going too slow - sql

Question

I'm trying to copy 60 Million Records in other Table with the Clustered Index with Fetching. but after 20 Million Records it's going too Slow. I dont no what should i do. can anybody help me please. hier is my Time counting.
1000000 Million Min: 1
2000000 Million Min: 0
3000000 Million Min: 0
4000000 Million Min: 2
5000000 Million Min: 2
6000000 Million Min: 1
7000000 Million Min: 0
8000000 Million Min: 1
9000000 Million Min: 0
10000000 Million Min: 1
11000000 Million Min: 0
12000000 Million Min: 1
13000000 Million Min: 1
14000000 Million Min: 0
15000000 Million Min: 1
16000000 Million Min: 1
17000000 Million Min: 1
18000000 Million Min: 0
19000000 Million Min: 1
20000000 Million Min: 3
21000000 Million Min: 3
22000000 Million Min: 4
23000000 Million Min: 5
24000000 Million Min: 4
25000000 Million Min: 4
26000000 Million Min: 4
27000000 Million Min: 4
28000000 Million Min: 5
29000000 Million Min: 5
30000000 Million Min: 5
31000000 Million Min: 6
32000000 Million Min: 7
33000000 Million Min: 7
34000000 Million Min: 8
35000000 Million Min: 8
36000000 Million Min: 9
37000000 Million Min: 8
38000000 Million Min: 10
39000000 Million Min: 10
40000000 Million Min: 11
41000000 Million Min: 11
42000000 Million Min: 11
43000000 Million Min: 12
44000000 Million Min: 11
45000000 Million Min: 12
46000000 Million Min: 12
47000000 Million Min: 14
48000000 Million Min: 13
49000000 Million Min: 13
50000000 Million Min: 14
51000000 Million Min: 15
52000000 Million Min: 14
53000000 Million Min: 16
54000000 Million Min: 18
55000000 Million Min: 18
56000000 Million Min: 20
57000000 Million Min: 19
58000000 Million Min: 21
59000000 Million Min: 19
declare
#RecNo Int
, #RecCount Int
, #RecordST nvarchar(max)
, #str_date datetime
, #end_date datetime;
Set #RecNo = 0
select #RecCount = 1000000
While 1 = 1
Begin
set #str_date = getdate();
Insert Into dbo.test2(
ap_id
,lipt_id
,li_cntr
)
select
ap_id
,lipt_id
,li_cntr
from dbo.test
order by ap_id, lipt_id, li_cntr
offset #RecNo rows
fetch next #RecCount rows only;
if ##ROWCOUNT = 0
break
Set #RecNo += 1000000;
set #end_date = GETDATE() ;
set #RecordST = cast(#RecNo as nvarchar(max)) + ' Million Min:'+cast(DATEDIFF(MINUTE,#str_date,#end_date) as nvarchar(max))
RAISERROR(#RecordST,0,0) WITH NOWAIT
end

Answer 1

First of all, you need drop all constraints like unique, PK and etc. It's the bottleneck for each insert in an existing table.
Secondly, If you insert into the table much more records than it has now then you may increase performance using SELECT INTO statement instead INSERT. But remember that SELECT INTO creates a new table so you would need to think how to append records which were there before.
Last but not the least, you can use loops and insert 1M record by batch.