Oracle vs. SQL Server- War of the Indices

#SQLSatATL
War of the Indices- Oracle vs.
SQL Server
Kellyn Pot’Vin-Gorman

#SQLSatATL 2
Kellyn Pot’Vin-Gorman
Technical Intelligence Manager for the Office of CTO,
Delphix
• Multi-platform DBA, (Oracle, MSSQL, MySQL, Sybase,
Postgres…..)
• Oracle ACE Director, (Alumni)
• Oak Table Network
• APEX Women in Technology Award, CTA 2014
• STEM education with Raspberry Pi and Python
• Liaison for Denver SQL Server User Group
• Rocky Mountain Oracle User Group President
• Author, blogger, (http://dbakevlar.com)

#SQLSatATL 3
Agenda
Background1
Platform Translations2
Test Case and Goal3
Code and Discussion4
Analysis and Summary5

#SQLSatATL 4
The What
Azure SQL Database AWS with Oracle 11.2.0.4

#SQLSatATL 5
The Why
• Its interesting…to me, at least.
• VM was an issue, so moved
everything to the cloud.
• Two major players in the
database landscape.
• Good apples to “apfel”
comparison.

#SQLSatATL 6
Translations Graph

#SQLSatATL 7
FILLFACTOR is a setting for indexes in SQL Server. When you
create or rebuild an index, you can tell SQL Server what
percentage of each 8K data page used in the “leaf” level of the
index it should fill up.
Fill Factor in SQL Server

#SQLSatATL 8
PCT Increase in Oracle
PCTFREE is a block storage parameter used to specify how much
space should be left in a database block for future updates. For
example, for PCTFREE=10, Oracle will keep on adding new rows to a
block until it is 90% full. This leaves 10% for future updates (row
expansion). This defaults to 10% for indexes, but can be adjusted via
a index rebuild.

#SQLSatATL 9
SQL Server Index Writes- Not Subject to Page Splits

#SQLSatATL 10
SQL Server Index Processing Impacted by Random

#SQLSatATL 11
Fragmentation Doesn’t Exist in Oracle Indexes
In What Case Would You Rebuild?
• Significant # of logically deleted index nodes.
• Inefficient number of gets per access
So yes, there are times and situations you need to
rebuild.
The goal here is to see where each platform
performs better than the other.

#SQLSatATL 12
Test Case
• Create a table with three columns and two indexes.
• Insert, update and delete different amounts of data.
• check the storage of our index and any
fragmentation, storage anomalies.
• Repeat
• Check the storage repeatedly to see how it has
changed- page splits in SQL Server, leaf block splits
in Oracle

#SQLSatATL 13
Goal
1. Inspect the differences and similarities of
indexing in both platforms
2. The pros and cons of how index data is stored
and used in the database platforms.
http://dbakevlar.com/2017/04/oracle-sql-server-index-comparison/

#SQLSatATL 14
First Test, Build and Check

#SQLSatATL 15
Oracle Objects
CREATE TABLE ORA_INDEX_TST
(
C1 NUMBER NOT NULL
,C2 VARCHAR2(255)
,CREATEDATE TIMESTAMP DEFAULT CURRENT_TIMESTAMP)
;CREATE INDEX PK_INDEXPS ON ORA_INDEX_TST (C1);
CREATE INDEX IDX_INDEXPS ON ORA_INDEX_TST (C2);
ALTER TABLE ORA_INDEX_TST ADD CONSTRAINT OIT_PK
PRIMARY KEY(C1) USING INDEX PK_INDEXPS;
ALTER INDEX IDX_INDEXPS REBUILD PCTFREE 90 INITRANS 5;
ALTER INDEX PK_INDEXPS REBUILD PCTFREE 90 INITRANS 5;

#SQLSatATL 16
Oracle Support Objects
CREATE SEQUENCE C1_SEQ START WITH 1;
CREATE OR REPLACE TRIGGER C1_BIR
BEFORE INSERT ON ORA_INDEX_TST
FOR EACH ROW
BEGIN
SELECT C1_SEQ.NEXTVAL
INTO :new.C1
FROM DUAL;
END;
/

#SQLSatATL 17
Insert 7 Rows to Fill One Oracle Block
INSERT INTO ORA_INDEX_TST (C2, CREATEDATE)
VALUES (dbms_random.string('A', 200), SYSDATE);
……
……
VALUES (dbms_random.string('F', 200), SYSDATE);
VALUES (dbms_random.string('G', 200), SYSDATE);
COMMIT;

#SQLSatATL 18
Check the Block
SQL> ANALYZE INDEX PK_INDEXPS VALIDATE STRUCTURE;
SQL> SELECT LF_BLKS, LF_BLK_LEN, DEL_LF_ROWS,USED_SPACE, PCT_USED
FROM INDEX_STATS where NAME='PK_INDEXPS';
LF_BLKS LF_BLK_LEN DEL_LF_ROWS USED_SPACE PCT_USED
---------- ---------- ----------- ---------- ----------
1 7924 0 1491 19
As expected- 1 leaf block for the seven
rows.

#SQLSatATL 19
Adjust Index and Then Insert 8th Row
ALTER INDEX IDX_INDEXPS REBUILD PCTFREE 90
INITRANS 5;
Yes, we’ve just adjusted the pctfree to 90%!
Consider what this will do to our index storage now that we’ve
rebuilt this allowing for only 10% usage in each block.
Insert the 8th row:
VALUES (dbms_random.string(‘H', 200), SYSDATE);

#SQLSatATL 20
After Change to Pct Free
SQL> ANALYZE INDEX PK_INDEXPS VALIDATE STRUCTURE;
SQL> SELECT LF_BLKS, LF_BLK_LEN, DEL_LF_ROWS,USED_SPACE,
PCT_USED FROM INDEX_STATS where NAME='PK_INDEXPS';
LF_BLKS LF_BLK_LEN DEL_LF_ROWS USED_SPACE PCT_USED
---------- ---------- ----------- ----------
8 8229 0 2369 32

#SQLSatATL
SQL Server’s Turn

#SQLSatATL 22
SQL Server Objects
CREATE TABLE SQL_INDEX_TST (c1 INT NOT NULL,
c2 CHAR (255),
createdate DATETIME NOT NULL DEFAULT GETDATE());
CREATE INDEX CL2_INDEX_TST ON SQL_INDEX_TST(C2);
GO
ALTER TABLE SQL_INDEX_TST
ADD CONSTRAINT PK_CLINDX_TST PRIMARY KEY NONCLUSTERED (c1);

#SQLSatATL 23
First Interesting Hurdle- SQL Server
Inserts and Updates
may fail due to
challenge of data
beyond range

#SQLSatATL 24
Insert 7 Rows to Fill up Initial SQL Server Page
INSERT INTO SQL_INDEX_TST(c1,c2) VALUES (1, 'a');
GO

#SQLSatATL 25
Alter Index Fillfactor and Insert 8th Row
ALTER INDEX CL_INDEX_TST ON dbo.SQL_Index_tst
REBUILD WITH (FILLFACTOR = 10);
GO
Now insert the 8th row in:
GO

#SQLSatATL 26
Check Statistics and Page Data on Index
SELECT
OBJECT_SCHEMA_NAME(ios.object_id) + '.' +
OBJECT_NAME(ios.object_id) as table_name,
i.name as index_name, leaf_allocation_count,
nonleaf_allocation_count
FROM sys.dm_db_index_operational_stats(DB_ID(),
OBJECT_ID('dbo.SQL_INDEX_TST'),NULL, NULL) ios
INNER JOIN sys.indexes i ON i.object_id =
ios.object_id AND i.index_id = ios.index_id;

#SQLSatATL 28
Second Test, Build and Check

#SQLSatATL 29
Data Loads into Oracle
SQL> Begin
For IDS in 1..1000000
Loop
VALUES (dbms_random.string('X', 200),
SYSDATE);
Commit;
End loop;
End;
/

#SQLSatATL 30
Check Data and Delete Data
SQL> select count(*) from ora_index_tst;
COUNT(*)
----------
1000008
SQL> delete from ora_index_tst
where c2 like '%200%';
437 rows deleted.
SQL> commit;
Commit complete.
10% PCT Free- Time Elapsed 2 minutes, 12 seconds
90% PCT Free- Time Elapsed 7 minutes, 3 seconds

#SQLSatATL 31
Resulting Index Fragmentation and Storage
SELECT LF_BLKS, LF_BLK_LEN, DEL_LF_ROWS,USED_SPACE, PCT_USED FROM
INDEX_STATS;

#SQLSatATL 32
Ending Row Count

#SQLSatATL 35
SQL Server Insert
declare @id int
select @id = 9 --already inserted 8 rows
while @id >= 0 and @id <= 1000000
begin
insert into sql_index_tst (c1,c2) values(@id,
'DKUELKJ' + convert(varchar(7), @id))
select @id = @id + 1
end
Default Fill Factor- Elapsed Time: 4 minutes, 43 seconds
10% Fill Factor- Elapsed time: 23 minutes, 18 seconds

#SQLSatATL 36
Check Page Splits in SQL Server
SELECT
OBJECT_SCHEMA_NAME(ios.object_id) + '.' +
OBJECT_NAME(ios.object_id) as table_name
,i.name as index_name
,leaf_allocation_count
,nonleaf_allocation_count
FROM sys.dm_db_index_operational_stats(DB_ID(),
OBJECT_ID('dbo.SQL_Index_tst'),NULL, NULL) ios
INNER JOIN sys.indexes i ON i.object_id = ios.object_id
AND i.index_id = ios.index_id;

#SQLSatATL 37
Page Splits Observed

#SQLSatATL 38
Check Fragmentation in SQL Server
SELECT
OBJECT_SCHEMA_NAME(ips.object_id) + '.' +
OBJECT_NAME(ips.object_id) as table_name
,ips.avg_fragmentation_in_percent
,ips.fragment_count
,page_count
FROM
sys.dm_db_index_physical_stats(DB_ID(),
OBJECT_ID('dbo.SQL_Index_tst'

#SQLSatATL 39
Fragmentation Results

#SQLSatATL 40
Third Test, Build and Check

#SQLSatATL
Clustered Indexes vs. Oracle IOTs
Oracle Index Organized Tables are most similar to
SQL Server Clustered Indexes.
How do those compare?

#SQLSatATL
Index Organized Table, (IOT)
• Variation of a primary b-tree index
• The index IS the table
• Data is sorted

#SQLSatATL
Oracle IOT Syntax
CREATE TABLE ora_tst_iot(
c1 NUMBER,
c2 varchar2(255),
CREATEDATE timestamp DEFAULT CURRENT_TIMESTAMP,
CONSTRAINT pk_ora_iot PRIMARY KEY (c1))
ORGANIZATION INDEX
TABLESPACE users
PCTTHRESHOLD 20
OVERFLOW TABLESPACE users;

#SQLSatATL
Supporting Features
• Created Sequence for PK on C1 column
• Created Trigger to insert next value in C1 on insert.
• The % Threshold set to 20
• No compression
• Loaded from my original table ORA_INDEX_TST

#SQLSatATL
Data Load and Validation

#SQLSatATL
IOT Vulnerabilities
SQL> SELECT 'Chained or Migrated Rows =
'||value
FROM v$sysstat
WHERE name = 'table fetch continued
row';
Chained or Migrated Rows = 73730

#SQLSatATL
Findings
C2 column has significant data and without C1, has a
difficult time for access.
• Disable trigger for sequence and then load table
with simplified data, then rebuild.
• ALTER TABLE ORA_IOT_TST REBUILD;

#SQLSatATL 49
After Issuing a Move Statement on an IOT
Tablespace
Extent
Block
Row
After Move
Command

#SQLSatATL
After More Updates/Deletes/Inserts

#SQLSatATL
So PCT Free
As discussed, Pct Free is how much free is to be left
at the end of a block…90%...hmm…

#SQLSatATL
Comparisons- Pct Free Vs. Fill Factor
10% Fill Factor in SQL Server and 1 million insert: Elapsed time: 23
minutes, 18 seconds
90% PCTFree in Oracle and 1 million insert: 7 min, 12 seconds
100% Fill Factor in SQL Server and 1 million insert: Elapsed Time: 4
minutes, 43 seconds
0% PCTFree in Oracle and 1 million insert: 1 min, 8 seconds
REBUILD of the Oracle IOT to make it 90% free in each block? Elapsed
Time: 8 hrs, 21 minutes, 12 seconds

#SQLSatATL
Clustered Index in SQL Server
• Data is physically sorted in clustered index by
default.
• Optimizer usage specific- clustered index seek
• Works best with sequential data, identity columns
and order dates.
• Option to randomize the writes on the index can
deter from hot spots.

#SQLSatATL
SQL Server Negatives
• Heavily vulnerable to fragmentation over standard
Oracle indexing.
• Last Page Insert Latch Contention- not an issue in
Oracle.
• Subject to hotspots, (as discussed.)
• Page Splits- hit performance HARD, especially
tran log.
• Fillfactor is hit or miss config in some systems.

#SQLSatATL
Summary- Clustered Index
Clustered Index:
• Less overhead during transactional processing for
inserts, updates and deletes
• Improved performance on queries of data to be sorted
in sequential order.
• Similar performance for complex queries and less sort
temp usage.
• Clustered Indexes are common place, IOTs have limited
use case.

#SQLSatATL
Summary: IOT
• Will require more maintenance if the IOT experiences
high processing including inserts, updates and deletes.
• DBCC rebuilds of a clustered index uses less resources
and doesn’t impact the transaction log as it does
Oracle’s rollback and archive log.
• It was easier to build the table with a high pct free
storage configuration and then do an insert of the
data, then drop the old table than to do an “alter
move” command.

Oracle vs. SQL Server- War of the Indices

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