Юра Гуляев. Oracle tables

ORACLE TABLES
Juri Guljajev

WHAT WILL WE TALK ABOUT?
External

Temporary
Tables
Relational
Heap organized
(“normal”)
Object
Index organized
(IOT)

LITTLE THEORY - HOW DATABASE STORE DATA?
• Smallest unit of data in Oracle is data block.
• Default size of data block is 8 kilobytes.
• Normally only one table rows can be added into one data block
• Database tries to store the whole row in one block

Customer id = 1
Customer id = 2

CUSTOMER Data block

LITTLE THEORY - ROWID
ROWID looks like AAAAaoAATAAABrXAAA
OOOOOOFFFBBBBBBRRR
• OOOOOO: The data object number that identifies the
database segment (AAAAao in the example).
• FFF: The tablespace-relative datafile number of the datafile
that contains the row (file AAT in the example).
• BBBBBB: The data block that contains the row
(block AAABrX in the example).
• RRR: The row in the block. (AAA in the example)

LITTLE THEORY - INDEX IN HEAP TABLE
Index is using ROWID to point on data from table.

SELECT * FROM customer WHERE id = 1;

HEAP ORGANISED - KEY FEATURES
• Unordered collection of rows
• Retrieval order is not guaranteed
• Rows are inserted where they fit best
• Generally better DML performance (in compare to IOT)
• Worse query performance by PK (in compare to IOT)
• Can be stored in table cluster

HEAP ORGANIZED - PCTFREE
The PCTFREE parameter sets the minimum percentage
of a data block to be reserved as free space for possible
updates to rows that already exist in that block.
FREE
CREATE TABLE test
( id NUMBER) Data block
PCTFREE 10
PCTFREE 10;

HEAP ORGANISED - PCTFREE
INSERT (example)
• 1 row size is: 5 bytes + 1900 bytes = 1905 bytes
• PCTFREE 10: (8192B – 10%) / 1905B = 3 rows

FREE
FREE

PCTFREE 10 PCTFREE 50

3 rows 2 rows

UPDATE (example)
Rows, that can’t fit into block after update were moved to
new data block and references were left in old data block.
ROWID of migrated row is not changed.
OLD BLOCK NEW BLOCK
PCTFREE 10
UPDATE UPDATE Ref left here ROW
First row
PCTFREE 10 PCTFREE 10
updated
1 row from old
3 rows block
2 rows left

UPDATE
Table, that have PCTFREE 50 have enough storage room
to fit added data into the same data block.

FREE

PCTFREE 50
PCTFREE 50 UPDATE
2 rows
2 rows

• Better query performance
• Better storage usage
• Use with caution (set PCTFREE 50, but rows are filled
by 80% with insert)

HEAP/INDEX ORGANISED - PARTITIONING
Partitioning helps to improve performance with high data
volumes and allows DBAs to manage data in more
convenient way.

Partition 1
Partition 2

Non-partitioned table Partitioned table

Partition n

Table can be partitioned by
• Range (for historical data, often partitioned by date
column)
• Hash (no obvious partitioning column)
• List (to group data specifically by some known values)

Range and List partitions may have subpartitions.

Indexes on partitioned table can be global or local partitioned.
• Local
• Maps on table partitions, so easier to maintain
• Unique index can be local, but partitioning key must be
part of index
• Global
• Has own partitions definitions
• Can be partitioned by range or hash

INDEX ORGANISED - KEY FEATURES
• Stored in a variation of a B-tree index structure
• Primary key stores all rows
• Fast access by primary key (specially range scan)
• DML performance might be worse (in compare to
HEAP)
• Take less room on disk (no separate primary key
storage required)
• Cannot be stored in table cluster

PROS
• Fast access by PK
• Less storage for the same amount of data
• Data is ordered by PK
CONS
• Slower DML
• Secondary index can be slower and take more storage in
compare to index in HEAP table

TABLE CLUSTER
Group of tables that share common columns and store
related data in the same blocks.

IP_RESTRICTION
customer_id
CUSTOMER
customer_id
TIME_RESTRICTION
customer_id

TABLE CLUSTER
SELECT* FROM customer WHERE customer_id = :id;

SELECT * FROM ip_restriction JOIN time_restriction
USING(customer_id) WHERE customer_id = :id;

SELECT * FROM customer JOIN ip_restriction
USING(customer_id) JOIN time_restriction
USING(customer_id) WHERE customer_id = :id;

TABLE CLUSTER
In cluster single data block contains rows from several
clustered tables.

clustered unclustered

customer
customer
customer
customer time_retstr.
ip_retstr.

TABLE CLUSTER
And all data, that contains the same clustered key value
are stored together.
unclustered
CUSTOMER_ID FIRST_NAME LAST_NAME …
1 AAA BBB
2 CCC DDD

CUSTOMER_ID IP CUSTOMER_ID TIME
1 192.168.1.1 1 MON 8-18
1 192.168.1.2 1 WEN 10-15
2 68.1.1.1 2 MON 8-18

TABLE CLUSTER
And all data, that contains the same clustered key value
are stored together.
clustered
CUSTOMER_ID FIRST_NAME LAST_NAME …
1 AAA BBB
IP
192.168.1.1
192.168.1.2
TIME
MON 8-18
2 CCC DDD

TABLE CLUSTER
What you will get
• Disk I/O is reduced for joins of clustered tables.
• Access time improves for joins of clustered tables.
• Less storage is required to store related table and index data because
the cluster key value is not stored repeatedly for each row.
But be careful (do not use when)
• The tables are frequently updated.
• The tables frequently require a full table scans.
• The tables require truncating.

TABLE CLUSTER
There are 2 types of clusters
Index cluster
• Data is co-located within a single block based on a common
column index, so separate cluster index should be created
before adding table into cluster
Hash cluster
• Data is co-located within a single block based on a hash
key and a hash function (own hash function can be used)

TABLE CLUSTER
Index VS Hash clusters
• Hash is faster
• Hash take less storage
• For hash you should know number of hash keys
• Hash cluster size and keys number can’t be changed
• Hash cluster loads CPU more, than index cluster

Юра Гуляев. Oracle tables

Юра Гуляев. Oracle tables

More Related Content

What's hot (19)

Similar to Юра Гуляев. Oracle tables (20)

Recently uploaded (20)

Юра Гуляев. Oracle tables