Possibly the data is in cache, the first time takes some time, the second time it does a similar thing it goes faster because it doesn't have any physical io.
Sybase ASE - Performance Select Into Vs Insert Select
-
14-10-2022 - |
Domanda
I have seen that the performance of a select into is better than a insert/select combination as it is un-logged. But today I encountered a different scenario. I am doing a select into from a physical table into a temp table and it inserts 2.4M records in 410 seconds, but when I split this into a select into statement to create the table first and then insert the data using a insert/select the same query clicks 2.4M records in 10.6 seconds.
I am confused, what can be the reason?
Query 1
=======
select a, b, c
into #A
from table1
where a = 'XYZ'
and c = 'ABC'
2.4M records inserted in 410 seconds
Query 2
=======
select a, b, c
into #A
from table1
where 1=2
insert #A
select a, b, c
from table1
where a = 'XYZ'
and c = 'ABC'
2.4M records inserted in 10.6 seconds
After comment from Jean
Now its acting strange. If I execute query 1 first and then query 2, then the results are as above. But if I switch the order, query 1 runs in ~9 secs and query 2 in ~7 secs.
Plans
Query 1
-------
""
QUERY PLAN FOR STATEMENT 1 (at line 1).
""
""
STEP 1
The type of query is DECLARE.
""
""
QUERY PLAN FOR STATEMENT 2 (at line 2).
""
""
STEP 1
The type of query is SELECT.
""
1 operator(s) under root
""
|ROOT:EMIT Operator (VA = 1)
|
| |SCALAR Operator (VA = 0)
""
""
""
QUERY PLAN FOR STATEMENT 3 (at line 3).
""
""
STEP 1
The type of query is CREATE TABLE.
""
STEP 2
The type of query is INSERT.
""
5 operator(s) under root
""
|ROOT:EMIT Operator (VA = 5)
|
| |INSERT Operator (VA = 4)
| | The update mode is direct.
| |
| | |NESTED LOOP JOIN Operator (VA = 3) (Join Type: Inner Join)
| | |
| | | |SCAN Operator (VA = 0)
| | | | FROM OR List
| | | | OR List has up to 3 rows of OR/IN values.
| | |
| | | |RESTRICT Operator (VA = 2)(0)(0)(0)(10)(0)
| | | |
| | | | |SCAN Operator (VA = 1)
| | | | | FROM TABLE
| | | | | ABCD.dbo.ITR
| | | | | a
| | | | | Using Clustered Index.
| | | | | Index : ITR_typ_imnt_cl_optn
| | | | | Forward Scan.
| | | | | Positioning by key.
| | | | | Keys are:
| | | | | id_typ_imnt ASC
| | | | | Using I/O Size 16 Kbytes for data pages.
| | | | | With LRU Buffer Replacement Strategy for data pages.
| |
| | TO TABLE
| | #A
| | Using I/O Size 16 Kbytes for data pages.
""
""
""
QUERY PLAN FOR STATEMENT 4 (at line 9).
""
""
STEP 1
The type of query is SELECT.
""
1 operator(s) under root
""
|ROOT:EMIT Operator (VA = 1)
|
| |SCALAR Operator (VA = 0)
""
""
Parse and Compile Time 0.
Adaptive Server cpu time: 0 ms.
Adaptive Server cpu time: 0 ms. Adaptive Server elapsed time: 0 ms.
Table: #A scan count 0, logical reads: (regular=2452707 apf=0 total=2452707), physical reads: (regular=0 apf=0 total=0), apf IOs used=0
Table: ABCD.dbo.ITR (a) scan count 3, logical reads: (regular=581980 apf=0 total=581980), physical reads: (regular=0 apf=0 total=0), apf IOs used=0
Execution Time 75.
Adaptive Server cpu time: 7500 ms. Adaptive Server elapsed time: 7546 ms.
Adaptive Server cpu time: 0 ms. Adaptive Server elapsed time: 0 ms.
Query 2
-------
""
QUERY PLAN FOR STATEMENT 1 (at line 1).
""
""
STEP 1
The type of query is DECLARE.
""
""
QUERY PLAN FOR STATEMENT 2 (at line 2).
""
""
STEP 1
The type of query is SELECT.
""
1 operator(s) under root
""
|ROOT:EMIT Operator (VA = 1)
|
| |SCALAR Operator (VA = 0)
""
""
""
QUERY PLAN FOR STATEMENT 3 (at line 3).
""
""
STEP 1
The type of query is CREATE TABLE.
""
STEP 2
The type of query is INSERT.
""
3 operator(s) under root
""
|ROOT:EMIT Operator (VA = 3)
|
| |INSERT Operator (VA = 2)
| | The update mode is direct.
| |
| | |RESTRICT Operator (VA = 1)(4)(0)(0)(0)(0)
| | |
| | | |SCAN Operator (VA = 0)
| | | | FROM TABLE
| | | | CERD_CORPORATE..INSTRUMENT
| | | | Table Scan.
| | | | Forward Scan.
| | | | Positioning at start of table.
| | | | Using I/O Size 2 Kbytes for data pages.
| | | | With LRU Buffer Replacement Strategy for data pages.
| |
| | TO TABLE
| | #A
| | Using I/O Size 16 Kbytes for data pages.
""
""
""
QUERY PLAN FOR STATEMENT 4 (at line 5).
""
""
STEP 1
The type of query is INSERT.
""
5 operator(s) under root
""
|ROOT:EMIT Operator (VA = 5)
|
| |INSERT Operator (VA = 4)
| | The update mode is direct.
| |
| | |NESTED LOOP JOIN Operator (VA = 3) (Join Type: Inner Join)
| | |
| | | |SCAN Operator (VA = 0)
| | | | FROM OR List
| | | | OR List has up to 3 rows of OR/IN values.
| | |
| | | |RESTRICT Operator (VA = 2)(0)(0)(0)(10)(0)
| | | |
| | | | |SCAN Operator (VA = 1)
| | | | | FROM TABLE
| | | | | CERD_CORPORATE.dbo.INSTRUMENT
| | | | | a
| | | | | Using Clustered Index.
| | | | | Index : INSTRUMENT_typ_imnt_cl_optn
| | | | | Forward Scan.
| | | | | Positioning by key.
| | | | | Keys are:
| | | | | id_typ_imnt ASC
| | | | | Using I/O Size 16 Kbytes for data pages.
| | | | | With LRU Buffer Replacement Strategy for data pages.
| |
| | TO TABLE
| | #A
| | Using I/O Size 2 Kbytes for data pages.
""
""
""
QUERY PLAN FOR STATEMENT 5 (at line 11).
""
""
STEP 1
The type of query is SELECT.
""
1 operator(s) under root
""
|ROOT:EMIT Operator (VA = 1)
|
| |SCALAR Operator (VA = 0)
""
""
Parse and Compile Time 0.
Adaptive Server cpu time: 0 ms.
Adaptive Server cpu time: 0 ms. Adaptive Server elapsed time: 0 ms.
Table: #A scan count 0, logical reads: (regular=1 apf=0 total=1), physical reads: (regular=0 apf=0 total=0), apf IOs used=0
Table: CERD_CORPORATE..INSTRUMENT scan count 0, logical reads: (regular=0 apf=0 total=0), physical reads: (regular=0 apf=0 total=0), apf IOs used=0
Adaptive Server cpu time: 0 ms. Adaptive Server elapsed time: 0 ms.
Table: #A scan count 0, logical reads: (regular=2493221 apf=0 total=2493221), physical reads: (regular=0 apf=0 total=0), apf IOs used=0
Table: CERD_CORPORATE.dbo.INSTRUMENT (a) scan count 3, logical reads: (regular=581980 apf=0 total=581980), physical reads: (regular=0 apf=0 total=0), apf IOs used=0
Execution Time 96.
Adaptive Server cpu time: 9600 ms. Adaptive Server elapsed time: 9580 ms.
Adaptive Server cpu time: 0 ms. Adaptive Server elapsed time: 0 ms.
Nessuna soluzione corretta
Altri suggerimenti