Partitioning refers to splitting one large table into smaller pieces. Each row in such table assigns to a single partition based on partitioning key. Common partitioning strategies are:

* HASH - maps rows to partitions based on hash function values;

* RANGE - maps data to partitions based on ranges that you establish for each partition;

* LIST - maps data to partitions based on explicitly specified values of partitioning key for each partition.

PostgreSQL supports partitioning via table inheritance. Each partition must be created as child table with CHECK CONSTRAINT. For example:

Partitioning refers to splitting one large table into smaller pieces. Each row in such table assigns to a single partition based on partitioning key. PostgreSQL supports partitioning via table inheritance. Each partition must be created as child table with CHECK CONSTRAINT. For example:

Despite the flexibilityofthis approachit has weakness. If query uses filteringtheoptimizer forcedto perform an exhaustive search and check constraints for each partition to determinepartitions fromwhichit shouldselect data. If the number of partitions is large the overhead may be significant.

Despite the flexibility this approachforcestheplannerto perform an exhaustive search and check constraints for each partition to determine whichone shouldpresent in the plan. If the number of partitions is large the overhead may be significant.

The`pg_pathman` module provides functions to manage partitions and partitioning mechanism optimized based on knowledge of the partitions structure. It stores partitioning configuration in the`pathman_config` table, each row of which contains single entry for partitioned table (relation name, partitioning key and type). During initialization the`pg_pathman` module caches information about child partitions in shared memory in form convenient to perform rapid search. Whenuser executesSELECT query pg_pathman analyzes conditions tree looking for conditions like:

The`pg_pathman` module provides functions to manage partitions and partitioning mechanism optimized based on knowledge of the partitions structure. It stores partitioning configuration in the`pathman_config` table, each row of which contains single entry for partitioned table (relation name, partitioning key and type). During initialization the`pg_pathman` module caches information about child partitions in shared memory in form convenient to perform rapid search. When SELECT queryexecutes`pg_pathman` analyzes conditions tree looking for conditions like:

Based on partitioning type and operator the`pg_pathman` searches corresponding partitions and builds the plan.

Based on partitioning type and operator the`pg_pathman` searches corresponding partitions and builds the plan. Current version of`pg_pathman` supports two partitioning types:

* RANGE - maps data to partitions based on ranges of partitioning key. Optimization is achieved by using binary search algorithm.

* HASH - maps rows to partitions based on hash function values (only INTEGER attributes at the moment);

* Optimize the execution of the NestedLoop join method;

* LIST-partitioning;

* HASH-partitioning for non integer attributes.

Consider an example of HASH partitioning. First create a table with some integer column:

If partitions are supposed to have indexes, then they should be created for parent table before partitioning. In this case pg_pathman will automaticaly create indexes for partitions. Then run create_hash_partitions() function with appropriate arguments:

This will create new partitions and move the data from parent to partitions.

Here is an example of the query with filtering by partitioning key and its plan:

Note that pg_pathman exludes parent table from the query plan. To access parent table use ONLY modifier:

Consider an example of RANGE partitioning. Create a table with numerical or date or timestamp column:

Consider an example of RANGE partitioning. Let's create a table to store log data:

Run create_range_partitions() function to create partitions so that each partition would contain data for one month:

It will create 60 partitions and move the data from parent to partitions.

To merge to adjacent partitions run merge_range_partitions() function:

To splitpartitionuse split_range_partition() function:

Run create_range_partitions() function to create partitions so that eachpartitionwould contain data for one day:

Now let's create new partition. You can use append_partition() or prepend_partition() functions:

It will create 365 partitions and move the data from parent to partitions.

New partitions are appended automaticaly by insert trigger. But it can be done manually with the following functions:

Here is an example of the query with filtering by partitioning key and its plan:

The first one creates partition with specified range. The second one creates partition with default interval and appends it to the partition list. It is also possible to attach an existing table as partition. For example we may want to attach an archive table (or even foreign table from another server) for outdated data:

To disable pg_pathman for some previously partitioned table use disable_partitioning() function:

To merge to adjacent partitions use function:

All sections and data will stay available and will be handled by standard PostgreSQL partitioning mechanism.

It is possible to manage partitions manually. After creating or removing child tables it's necessary to invoke function:

To split partition by value use function:

which updates internal structures in memory of`pg_pathman module`. For example, let's create new section for the`range_rel` from above:

To detach partition use:

CHECK CONSTRAINT must have the exact format:

* (VARIABLE >= CONST AND VARIABLE < CONST) for RANGE partitioned tables;

* (VARIABLE % CONST = CONST) for HASH partitioned tables.

It ispossible to create partition from foreign table as well:

Here isan example of the query with filtering by partitioning key and its plan:

Foreign table structure must exactly match the parent table.

In case when parent table is being dropped by DROP TABLE, you should invoke on_remove_partitions() function and delete particular entry from`pathman_config` table:

To disable pg_pathman for some previously partitioned table use disable_partitioning() function:

Ildar Musin <i.musin@postgrespro.ru> Postgres Professional Ltd., Russia

This module is sponsored by Postgres Professional Ltd., Russia

All sections and data will stay available and will be handled by standard PostgreSQL partitioning mechanism.

Подключим ее к имеющемуся разбиению:

Чтобы отсоединить ранее созданнуюили присоединеннуюсекцию воспользуйтесь функцией:

Чтобы отсоединить ранее созданную секцию, воспользуйтесь функцией:

{

Oidchild_oid;

int64min;

int64max;

FmgrInfocmp_func;

char*schema;

schema=get_extension_schema();

prel=get_pathman_relation_info(relid,NULL);