1. Exadata - SMART SCAN testing
-------------------------------------------Samrt scan works with cell offloading which relate to offloaded the sql processing from the database layer to the
cell (storage) layer.
Smart scan is the access mechanism to offload data from storage layer. For example passing only required data
blocks after applying predicate filters at the cell layer instead of sending every possible blocks from cell server
to database server.
Flash current buffer cache
====================
alter system flush buffer_cache;
Create a table for testing
=======================
create table sales_SM_SC as
select
mod(rownum,5) as channel_id,
mod(rownum,1000) as cust_id ,
5000 as amount_sold,
to_date
('01.' || lpad(to_char(mod(rownum,12)+1),2,'0') || '.2007' ,'dd.mm.yyyy')
as time_id
from dual connect by level<=2e4;
Check the table size
=================
SQL> select bytes/1024/1024 as SizeMB from user_segments where segment_name='SALES_SM_SC';
SIZEMB
---------.5625
SQL> alter table sales nologging;
Table altered.
Insert data
============
insert /*+ append */ into sales_SM_SC select
channel_id, cust_id,amount_sold, time_id
from sales;
12399984 rows created.
/
12399984 rows created.
SQL> commit;
Commit complete.
SQL> select bytes/1024/1024 as SizeMB from user_segments where segment_name='SALES_SM_SC';
SIZEMB
---------656
Gather Statistics
==============
SQL> exec dbms_stats.gather_table_stats('SH','SALES_SM_SC')
SQL>

2. PL/SQL procedure successfully completed.
Check the Query Processing speed without Smart Scan:
--------------------------------------------------------------------SQL> alter session set cell_offload_processing=false;
Session altered.
--------------------------------------------------------------------------------------------------------------------------------------NOTE : Inside the SQL statement optimizer hint to disables Smart Scan for the query
select /*+ OPT_PARAM('cell_offload_processing' 'false') */ count(*) from SALES_SM_SC where
channel_id=1
------------------------------------------------------------------------------------------------------ --------------------------------SQL> set timing on
select /* NO_SMART_SCAN */ count(*) from SALES_SM_SC where channel_id=1;
SQL>
COUNT(*)
---------4000
Elapsed: 00:00:16.19
SQL> /
COUNT(*)
---------4000
Elapsed: 00:00:15.68
WIth Smart Scan:
---------------------SQL> set timing off;
SQL> alter session set cell_offload_processing=true;
Session altered.
SQL> set timing on
SQL> select /* WITH_SMART_SCAN */ count(*) from SALES_SM_SC where channel_id=1;
COUNT(*)
---------4000
Elapsed: 00:00:23.75
SQL> /
COUNT(*)
---------4000
Elapsed: 00:00:00.05
Note: Without cell_offload_processing query took 15:68 seconds where with cell_offload_processing
it took 00:05 seconds.

3. Query to check Predicate offload and smart scan
---------------------------------------------------------------SQL> select a.name, b.value/1024/1024 MB
2 from v$sysstat a, v$mystat b
3 where a.statistic# = b.statistic# and
4 (a.name in ('physical read total bytes',
5
'physical write total bytes',
6
'cell IO uncompressed bytes')
7 or a.name like 'cell phy%');
NAME
MB
---------------------------------------------------------------- ---------physical read total bytes
53.0703125
physical write total bytes
0
cell physical IO interconnect bytes
.188957214
cell physical IO bytes sent directly to DB node to balanceCPU u
0
cell physical IO bytes saved during optimized file creation
0
cell physical IO bytes saved during optimized RMAN file restore
0
cell physical IO bytes eligible for predicate offload
53.0625
cell physical IO bytes saved by storage index
0
cell physical IO interconnect bytes returned by smart scan
.181144714
cell IO uncompressed bytes
53.0625
10 rows selected.
So query is getting almost every blocks from predicate offload. Smart scan is required to get only 0.18MB data.
Explain Plan for Without SMART_SCAN
-----------------------------------SQL> set timing off;
SQL> select sql_id from v$sql where sql_text like '%NO_SMART_SCAN%' and sql_text not like '%like%';
SQL_ID
------------9fmuwnmmrvapv
SQL> select plan_table_output from table (dbms_xplan.display_cursor('9fmuwnmmrvapv'));
PLAN_TABLE_OUTPUT
-------------------------------------------------------------------------------SQL_ID 9fmuwnmmrvapv, child number 0
------------------------------------select /* NO_SMART_SCAN */ count(*) from SALES_SM_SC where channel_id=1
Plan hash value: 1381054164
-----------------------------------------------------------------------------------------| Id | Operation
| Name
| Rows | Bytes | Cost (%CPU)| Time
-----------------------------------------------------------------------------------------| 0 | SELECT STATEMENT
| 1 | SORT AGGREGATE
|
|
|
|
|
1|
| 22874 (100)|
3|
|
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
|
|
|

4. |* 2 | TABLE ACCESS STORAGE FULL| SALES_SM_SC | 3545K| 10M| 22874 (2)|00:04:35 |
------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
--------------------------------------------------2 - filter("CHANNEL_ID"=1)
19 rows selected.
Explain Plan for SMART SCAN
----------------------------------------SQL> SQL> select sql_id from v$sql where sql_text like '%WITH_SMART_SCAN%' and sql_text not like
'%like%';
SQL_ID
------------8rb96afm261ry
SQL> select plan_table_output from table (dbms_xplan.display_cursor('&SQLID'));
Enter value for sqlid: 8rb96afm261ry
old 1: select plan_table_output from table (dbms_xplan.display_cursor('&SQLID'))
new 1: select plan_table_output from table (dbms_xplan.display_cursor('8rb96afm261ry'))
PLAN_TABLE_OUTPUT
-------------------------------------------------------------------------------SQL_ID 8rb96afm261ry, child number 0
------------------------------------select /* WITH_SMART_SCAN */ count(*) from SALES_SM_SC where
channel_id=1
Plan hash value: 1381054164
-----------------------------------------------------------------------------------------| Id | Operation
| Name
| Rows | Bytes | Cost (%CPU)|Time
|
-----------------------------------------------------------------------------------------| 0 | SELECT STATEMENT
| 1 | SORT AGGREGATE
|
|
|
|
|
1|
| 22874 (100)|
3|
|
|
|
PLAN_TABLE_OUTPUT
-------------------------------------------------------------------------------|* 2 | TABLE ACCESS STORAGE FULL| SALES_SM_SC | 3545K| 10M| 22874 (2)|00:04:35 |
------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
--------------------------------------------------2 - storage("CHANNEL_ID"=1)

5. filter("CHANNEL_ID"=1)
21 rows selected.
NOTE: The Storage Layer did filter on the predicate channel_id=1 before transmitting the result to the
Database Layer, which is the reason for the reduced runtime.
---------------------------------------2nd Example SMART SCAN
--------------------------------------SQL> conn sh/sh
Connected.
SQL> set autotrace on
SQL> set timing on
SQL> select count (*) from customers where cust_valid='B';
COUNT(*)
---------0
Elapsed: 00:00:07.08
Execution Plan
---------------------------------------------------------Plan hash value: 296924608
-------------------------------------------------------------------------------| Id | Operation
| Name
| Rows | Bytes | Cost (%CPU)| Time
|
-------------------------------------------------------------------------------| 0 | SELECT STATEMENT
|
| 1 | 2 | 10245 (1)| 00:02:03 |
| 1 | SORT AGGREGATE
|
|
1|
2|
|
|
|* 2 | TABLE ACCESS STORAGE FULL| CUSTOMERS | 65588 | 128K| 10245 (1)| 00:02:03 |
-------------------------------------------------------------------------------Predicate Information (identified by operation id):
--------------------------------------------------2 - storage("CUST_VALID"='B')
filter("CUST_VALID"='B')
Statistics
---------------------------------------------------------1 recursive calls
0 db block gets
36884 consistent gets
36880 physical reads
0 redo size
525 bytes sent via SQL*Net to client
519 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed

6. SQL> set autotrace off
SQL> select a.name, b.value/1024/1024 MB
from v$sysstat a, v$mystat b
where a.statistic# = b.statistic# and
(a.name in ('physical read total bytes',
'physical write total bytes',
'cell IO uncompressed bytes')
or a.name like 'cell phy%');
NAME
MB
---------------------------------------------------------------- ---------physical read total bytes
288.25
physical write total bytes
0
cell physical IO interconnect bytes
.222740173
cell physical IO bytes sent directly to DB node to balanceCPU u
0
cell physical IO bytes saved during optimized file creation
0
cell physical IO bytes saved during optimized RMAN file restore
0
cell physical IO bytes eligible for predicate offload
288.070313
cell physical IO bytes saved by storage index
0
cell physical IO interconnect bytes returned by smart scan
.043052673
cell IO uncompressed bytes
288.070313
10 rows selected.
Elapsed: 00:00:00.01
SQL>
select distinct event, total_waits, time_waited/100 wait_secs, average_wait/100 avgwait_secs
from v$session_event e, v$mystat s
where event like 'cell%' and e.sid=s.sid;SQL> 2 3
EVENT
TOTAL_WAITS WAIT_SECS AVGWAIT_SECS
---------- ---------------------------------------------------------------cell single block physical read
52
.59
.0113
cell multiblock physical read
1
.02
.0217
cell smart table scan
191
6.96
.0364
Elapsed: 00:00:00.50
Open another Session, update the query without commit:
+++++++++++++++++++++++++++++++++++++++++++++
SQL> update customers
2 set cust_credit_limit=1.5*cust_credit_limit
3 where cust_id > 500000;
Go to first session
-------------------SQL> select count (*) from customers where cust_valid='B';
COUNT(*)
---------0
Elapsed: 00:01:43.12 ======> Finding1 (more time to get query output)
AME
MB
---------------------------------------------------------------- ---------physical read total bytes
607.484375
physical write total bytes
0
cell physical IO interconnect bytes
186.811409 ---->find2: more data to interconnect

7. cell physical IO bytes sent directly to DB node to balanceCPU u
0
cell physical IO bytes saved during optimized file creation
0
cell physical IO bytes saved during optimized RMAN file restore
0
cell physical IO bytes eligible for predicate offload
576.140625
cell physical IO bytes saved by storage index
0
cell physical IO interconnect bytes returned by smart scan
155.467659 ---->find3: More data was returned
cell IO uncompressed bytes
576.140625
10 rows selected.
Elapsed: 00:00:00.07
SQL> select distinct event, total_waits, time_waited/100 wait_secs, average_wait/100 avgwait_secs
from v$session_event e, v$mystat s
where event like 'cell%' and e.sid=s.sid; 2 3
EVENT
TOTAL_WAITS WAIT_SECS AVGWAIT_SECS
---------- ---------------------------------------------------------------cell single block physical read
4009 89.91 ---> find4
.0224
[Wait is more than .59sec]
cell multiblock physical read
cell smart table scan
1
375
.02
.0217
14.06
.0375
Elapsed: 00:00:00.14
Note: All because for uncommited transaction ---working as traditional buffer cache