MySQL Partitioning

1Copyright 2005 MySQL AB The World’s Most Popular Open Source Database

Partitioning in MySQL 5.1 and onwards

Dr. Mikael Ronström, Senior Software ArchitectMySQL AB

[email protected]


Why Partitioning?

• For Large Tables:• ”Divide and Conquer”• Easier maintenance• Performance improvement for queries• Control data placement on disk devices• Control data placement on Cluster nodes• Preparatory step for Parallel Queries


Partitioned Tables

• Partitioned Tables are standard MySQL tables– Can be part of all constructs where tables are

used– Complex select queries, Stored Procedures,

Triggers, Views

• Easy to ALTER TABLE into partitioned table– Syntax from CREATE TABLE can also be used

in ALTER TABLE• Easy to drop partitioning on a table

– ALTER TABLE t1 REMOVE PARTITIONING;


Partition Management

• Fast Deletion of entire parts of a table• Fast reorganisation of one part of a table• Fast reorganisation of partition boundaries• Fast adding of new partitions• Fast split/merge of partitions


MySQL Partitioning Types

• Range Partitioning

• List Partitioning

• Hash Partitioning

• Composite Partitioning


Storage Engines

• Partition applies to all storage engines– MyISAM– InnoDB– Archive– NDB Cluster– Falcon

• Exceptions– Merge

• Don’t mix storage engines in one table for now (5.1 limitation)– Example:

– Archive Engine for really old data (> 10 years)– MyISAM for medium old data (> 1 year)– InnoDB for current data


Key Partitioning

• Definition– Same as Hash partitioning except that MySQL

decides the hash function using the given fields• Benefits

– Very good hash function– Tight integration with MySQL Cluster partitioning

• Drawbacks– Same as for Hash partitioning


LINEAR HASH/KEY partitioning

• The normal HASH/KEY uses a modulo function to spread records => Even distribution of data among partitions

• Also leads to full rebuild of table for ADD/COALESCE Partition

• LINEAR HASH/KEY partitions use an algorithm based on linear hashing which means that some partitions will have twice as much data as others if the number of partitions is not on the form 2 ^ n

• LINEAR HASH/KEY only requires rebuild of a number of the partitions, thus faster partition management at the cost of a slight imbalance


Partition Function• PARTITION BY RANGE(f(f1,f2,f3))• Partition function must always deliver integer result

(5.1 limitation)• Partition function can contain any number of fields, but

must contain at least one field• If primary key is defined, no fields outside of primary

key is allowed in partition function• Partition function can contain a large variety of

character functions, date functions and mathematical functions

• If unique key is defined on a table, no fields outside of unique key is allowed in partition function (this limitation does not exist for tables in MySQL Cluster)


Partition Options

MAX_ROWSMIN_ROWSNODEGROUP (only MySQL Cluster)DATA DIRECTORY (only MyISAM)INDEX DIRECTORY (only MyISAM)COMMENT


INFORMATION SCHEMA for Partitioning

• Provides information of:– Partition names– Where partitions are stored– Information about partition types– Information about partition functions– Number of rows per partition– Average row length in partitions– Other attributes of partitions (timestamps, …)

• Support SHOW CREATE TABLE• Support SHOW TABLE STATUS

– Will be displayed as Create option PARTITIONED


EXPLAIN for queries usingPartitioned Tables

• Explains which partitions will be actually scanned in a query– Gives you everything that EXPLAIN provides– Plus a list of partition names used in the query

• Use EXPLAIN PARTITIONS to understand:– How partition pruning affects the query– Which indexes are used

• might be affected by partitioning– If there is a better partitioning strategy


Partition Management

• ALTER TABLE t1 DROP PARTITION p0;• ALTER TABLE t1 ADD PARTITION (PARTITION p1);• ALTER TABLE t1 REORGANIZE PARTITION ….;• ALTER TABLE t1 COALESCE PARTITION 1;• ALTER TABLE t1 REBUILD PARTITION p0;• ALTER TABLE t1 OPTIMIZE PARTITION p0;• ALTER TABLE t1 CHECK PARTITION p0;• ALTER TABLE t1 ANALYZE PARTITION p0;• ALTER TABLE t1 REPAIR PARTITION p0;• ALTER TABLE t1 TRUNCATE PARTITION p0;


Drop RANGE/LIST Partition

2002 2003 2004 2005

ALTER TABLE t1 DROP PARTITION 2002


Add RANGE/LIST Partition

20062003 2004 2005

ALTER TABLE t1 ADD PARTITION (PARTITION 2006 VALUES IN (2006));

2006


ADD HASH/KEY partition(s)

ALTER TABLE t1 ADD PARTITION (PARTITION p4);

Old Partitions

New Partitions

p2 p3

p1 p2 p3 p4

p1


ADD LINEAR HASH/KEY partition(s)

ALTER TABLE t1 ADD PARTITION (PARTITION p4);

Old Partitions

New Partitions

p1 p2 p3

p2 p4


COALESCE HASH/KEY partition(s)

ALTER TABLE t1 COALESCE PARTITION 1;

p1 p2 p3

p1 p2 p3

p4Old Partitions

New Partitions


COALESCE LINEAR HASH/KEY partition(s)

ALTER TABLE t1 COALESCE PARTITION 1;

Old Partitions

New Partitions

p1 p2 p3

p2

p4


Using REORGANIZE partition to SPLIT a partition

Before_2002 2002_2003 2004_2005 2006_2007

2006 2007

ALTER TABLE t1 REORGANIZE PARTITION 2006_2007 INTO(PARTITION 2006 VALUES LESS THAN (2007),PARTITION 2007 VALUES LESS THAN (2008));


Using REORGANIZE partition to MERGE partitions

Before_2004 2004_2005 2006 2007

ALTER TABLE t1 REORGANIZE PARTITION 2006,2007 INTO(PARTITION 2006_2007 VALUES LESS THAN (2008));

2006_2007


Using REORGANIZE partition to balance partitions

Before_2004 2005 2006_Q1 2006-Q2

ALTER TABLE t1 REORGANIZE PARTITION 2006_Q1,2006_Q2 INTO(PARTITION 2006_M1_4 VALUES LESS THAN (DATE(’2006-05-01’),PARTITION 2006_M_5_8 VALUES LESS THAN (DATE(’2006-09-01’));

2006_M_5_82006_M_1_4


Using REORGANIZE partition to move partitions to new disk device

Before_2004 2005 2006 2007

ALTER TABLE t1 REORGANIZE PARTITION 2006 INTO(PARTITION 2006 DATA DIRECTORY ’/home/user/2006/data_file’

INDEX DIRECTORY ’/home/user/2006/index_file’ VALUES LESS THAN (2007));

2006


Using REBUILD partition to recreate partition

Before_2004 2005 2006 2007

ALTER TABLE t1 REBUILD PARTITION 2006;

2006


Partition Pruning

• Only scan needed partitions– Range optimisations for single-field function, YEAR(date) and

DATE_TO_DAYS(date) functions (RANGE partitioning)– Range optimisations for all LIST/HASH/KEY partitions

• Best use case:– Full table scans on non-indexed fields

• Example:– CREATE TABLE t1 (a int, index(a)) PARTITION BY HASH (a)

partitions 4;– CREATE TABLE t2 (a int, index(a));


Partition Pruning

SELECT * FROM Cars Where PRICE > 9000

8000-TSU564-198811000-YRG213-200513000-KAR365-2001

7000-SAG293-2004

8500-KHO297-200421100-GRO293-195612000-FBI007-2004

34000-SIE568-20041000-YUK333-1981

Price >9000

8000-TSU564-198811000-YRG213-200513000-KAR365-2001

7000-SAG293-2004 12000-FBI007-200421100-GRO293-19568500-KHO297-2004

1000-YUK333-1981

Results

34000-SIE568-200434000-SIE568-2004


Partition Pruning

Select *FROM Cars Where PRICE >9000 and COLOR= Red

8000-TSU564-198811000-YRG213-200513000-KAR365-2001

7000-SAG293-2004

8500-KHO297-200421100-GRO293-195612000-FBI007-2004

34000-SIE568-20041000-YUK333-1981

Price >9000

Results

8000-TSU564-198811000-YRG213-200513000-KAR365-2001

7000-SAG293-2004 12000-FBI007-200421100-GRO293-19568500-KHO297-2004

1000-YUK333-198134000-SIE568-2004


Dynamic Partitioning Pruning

SELECT * FROM t1, t2 WHERE t2.a = t1.a;

If t1 is inner loop it is possible to select only one partition in each of its scan (one scan per record in outer table t2).

If t1 is outer loop it has to scan all partitions.

Explanation: This works since there is an index on ‘a’that contains all partitioning fields and this is bound for each scan in inner loop


Partitioning and NULL values

• NULL values are allowed in partitioning fields• If a partitioning function is evaluated where one field is

NULL the result of the partitioning will be the smallest integer

• This also holds for VALUES IN (NULL) in List partitioned tables

• VALUES LESS THAN (NULL) is not allowed• VALUES LESS THAN MAXVALUE will include all

integers upto the biggest integer


Partititioning Implementation

TABLE t1 (Abstract table,frm-file for t1 exists,

Implemented byPartition handler)

Partition p1Handler Table

(no frm for partitions)

MyISAM/InnoDB/

Federated/…..


index_read Algorithm

SortedOutput stream

From Partition 1

SortedOutput stream

From Partition 2

SortedOutput stream

From Partition 3

SortedOutput stream

From Partition 4

Merge SortPart

Handler output


Insert in Partitioning Table

GOX 123 $ 3000 2001 YELLOW

YELLOW GREEN RED BLUE

Insert


Updating Partition

Yellow Blue Red Green

GOX 123 $ 3000 2001 Yellow

GOX 123 $ 3000 2001 Green

Delete Insert


Partitioning for MySQL Cluster

• Default for MySQL Cluster:– All tables in MySQL Cluster are partitioned– Default for an ENGINE=NDB is PARTITION BY KEY()

• User Defined Partitioning for MySQL Cluster– Supports same partitioning types as rest of MySQL (Beta using –new)– PARTITION BY KEY is fully integrated with NDB kernel– Partitions defined in MySQL mapped to partitions in NDB storage

engine, thus no extra overhead for many partitions– Partitioning makes manual placement of partitions possible

• NOTE:– No support for DROP PARTITION– Full table copy is always employed for Partition Management

• Locks entire table (=> not on-line)• More memory resources used• More processing resources


Cluster: Partitioning Controls Physical Distribution

• Accessing relevant partitions only (partition pruning) for a query optimizes communication costs

• A table no longer has to be distributed on all nodes• Altering the table partitioning can change the physical

distribution– Altering table partitioning is currently done as a copying

ALTER TABLE• Node groups can be populated on-line

– ALTER TABLE account ADD PARTITION (PARTITION P2 NODEGROUP 2)

– With future support for adding nodes (node groups) on-line, tables can be re-partitioned to populate the added nodes


Cluster: Partition by KeyCREATE TABLE service(user int unsigned,

service varchar, parameter

int)PRIMARY KEY (user, service)PARTITION BY KEY (user)ENGINE=NDBCLUSTER;

• PARTITION BY KEY enables us to place all user records from all tables in the same node group– Better locality of access for transactions towards a particular user

• Default number of partitions in MySQL Cluster == Number of nodes in cluster


Cluster: Default Tables

• ENGINE=NDB is translated to PARTITION BY KEY() ENGINE=NDB– PARTITION BY KEY() means by fields in primary key

• if no primary key exists it means by Hidden Key– a unique identifier generated by MySQL for tables

without primary keys in MySQL Cluster– PARTITION BY KEY() can be used also for non-clustered tables

• Only partition by primary key (no hidden key stuff)

• Default number of partitions for non-clustered partitioned tables is 1


Backup and Restore for partitioned tables in MySQL Cluster

SCENARIO DESCRIPTION:• Backup taken in cluster with 4 node groups• Restore performed in cluster with 2 node groups• Assume table manually partitioned to be in node group 0

and 3• What can be done for the partition in node group 3?• For mysqldump and Cluster Replication the table must

be created by the user before applying the user records/binlog


Nodegroup maps for ndb_restore

• Using ndb_restore it is possible to specify a mapping between node groups as specified in backup and the node groups set up by the restore program.

• Use parameter --ndb-nodegroup-map ’(3,1)(2,0)’• It needs a list of mappings from old nodegroup to new

nodegroup• An old nodegroup map can be mapped to more than one

nodegroup, in that case mappings are done on a round robin basis for those partitions

• Tables that haven’t explicitly set a nodegroup is not affected by this mapping


Future Roadmap

• Global Indexes– Unique indexes fully supported

• Foreign Key support• Import/Export Partitions to/from other tables• Even more on-line changes• Optimised locking/opening of tables

– Better performance• Mix storage engines in one table

– Example:– Archive Engine for really old data (> 10 years)– MyISAM for medium old data (> 1 year)– InnoDB for current data

• Enable queries on ”broken” tables– Query even when a partition is not available


Partitioning Limitations (5.1)

• Partitioning Function must return integer result• All partitions must use the same Storage Engine (with

same options)• Use of a partitioned table => open all partitions⇒Increases response time for partitioned tables with many

partitions (execution overhead very little)• Foreign Keys support is not available for partitioned tables

(on the roadmap for future release)


More information on Partitioning

• Documentation– http://dev.mysql.com/doc/refman/5.1/en/partitioni

ng.html• Blog

– http://mikaelronstrom.blogspot.com• Forums

– http://forums.mysql.com/list.php?106


Thank You!

Senior Software ArchitectDr. Mikael Ronström

MySQL AB

[email protected]

Documents

MySQL Partitioning