NOTE: this project is not under development anymore

pg_pathman supports Postgres versions [9.5..13], but most probably it won't be ported to 14 and later releases. Native partitioning is pretty mature now and has almost everything implemented in pg_pathman'; we encourage users switching to it. We are still maintaining the project (fixing bugs in supported versions), but no new development is going to happen here.

pg_pathman

The pg_pathman module provides optimized partitioning mechanism and functions to manage partitions.

The extension is compatible with:

• PostgreSQL 9.5, 9.6, 10, 11, 12, 13;
• Postgres Pro Standard 9.5, 9.6, 10, 11, 12;
• Postgres Pro Enterprise;

Take a look at our Wiki out there.

Overview

Partitioning means splitting one large table into smaller pieces. Each row in such table is moved to a single partition according to the partitioning key. PostgreSQL <= 10 supports partitioning via table inheritance: each partition must be created as a child table with CHECK CONSTRAINT:

CREATE TABLE test (id SERIAL PRIMARY KEY, title TEXT);
CREATE TABLE test_1 (CHECK ( id >= 100 AND id < 200 )) INHERITS (test);
CREATE TABLE test_2 (CHECK ( id >= 200 AND id < 300 )) INHERITS (test);

PostgreSQL 10 provides native partitioning:

CREATE TABLE test(id int4, value text) PARTITION BY RANGE(id);
CREATE TABLE test_1 PARTITION OF test FOR VALUES FROM (1) TO (10);
CREATE TABLE test_2 PARTITION OF test FOR VALUES FROM (10) TO (20);

It's not so different from the classic approach; there are implicit check constraints, and most of its limitations are still relevant.

Despite the flexibility, this approach forces the planner to perform an exhaustive search and to check constraints on each partition to determine whether it should be present in the plan or not. Large amount of partitions may result in significant planning overhead.

The pg_pathman module features partition managing functions and optimized planning mechanism which utilizes knowledge of the partitions' structure. It stores partitioning configuration in the pathman_config table; each row contains a single entry for a partitioned table (relation name, partitioning column and its type). During the initialization stage the pg_pathman module caches some information about child partitions in the shared memory, which is used later for plan construction. Before a SELECT query is executed, pg_pathman traverses the condition tree in search of expressions like:

VARIABLE OP CONST

where VARIABLE is a partitioning key, OP is a comparison operator (supported operators are =, <, <=, >, >=), CONST is a scalar value. For example:

WHERE id = 150

Based on the partitioning type and condition's operator, pg_pathman searches for the corresponding partitions and builds the plan. Currently pg_pathman supports two partitioning schemes:

• RANGE - maps rows to partitions using partitioning key ranges assigned to each partition. Optimization is achieved by using the binary search algorithm;
• HASH - maps rows to partitions using a generic hash function.

More interesting features are yet to come. Stay tuned!

Feature highlights

• HASH and RANGE partitioning schemes;
• Partitioning by expression and composite key;
• Both automatic and manual partition management;
• Support for integer, floating point, date and other types, including domains;
• Effective query planning for partitioned tables (JOINs, subselects etc);
• RuntimeAppend & RuntimeMergeAppend custom plan nodes to pick partitions at runtime;
• PartitionFilter: an efficient drop-in replacement for INSERT triggers;
• PartitionRouter and PartitionOverseer for cross-partition UPDATE queries (instead of triggers);
• Automatic partition creation for new INSERTed data (only for RANGE partitioning);
• Improved COPY FROM statement that is able to insert rows directly into partitions;
• User-defined callbacks for partition creation event handling;
• Non-blocking concurrent table partitioning;
• FDW support (foreign partitions);
• Various GUC toggles and configurable settings.
• Partial support of declarative partitioning (from PostgreSQL 10).

Installation guide

To install pg_pathman, execute this in the module's directory:

make install USE_PGXS=1

Important: Don't forget to set the PG_CONFIG variable (make PG_CONFIG=...) in case you want to test pg_pathman on a non-default or custom build of PostgreSQL. Read more here.

Modify the shared_preload_libraries parameter in postgresql.conf as following:

shared_preload_libraries = 'pg_pathman'

Important: pg_pathman may cause conflicts with some other extensions that use the same hook functions. For example, pg_pathman uses ProcessUtility_hook to handle COPY queries for partitioned tables, which means it may interfere with pg_stat_statements from time to time. In this case, try listing libraries in certain order: shared_preload_libraries = 'pg_stat_statements, pg_pathman'.

It is essential to restart the PostgreSQL instance. After that, execute the following query in psql:

CREATE SCHEMA pathman;
GRANT USAGE ON SCHEMA pathman TO PUBLIC;
CREATE EXTENSION pg_pathman WITH SCHEMA pathman;

Done! Now it's time to setup your partitioning schemes.

Security notice: pg_pathman is believed to be secure against search-path-based attacks mentioned in Postgres documentation. However, if your calls of pathman's functions doesn't exactly match the signature, they might be vulnerable to malicious overloading. If in doubt, install pathman to clean schema where nobody except superusers have CREATE object permission to avoid problems.

Windows-specific: pg_pathman imports several symbols (e.g. None_Receiver, InvalidObjectAddress) from PostgreSQL, which is fine by itself, but requires that those symbols are marked as PGDLLIMPORT. Unfortunately, some of them are not exported from vanilla PostgreSQL, which means that you have to either use Postgres Pro Standard/Enterprise (which includes all necessary patches), or patch and build your own distribution of PostgreSQL.

How to update

In order to update pg_pathman:

1. Install the latest stable release of pg_pathman.
2. Restart your PostgreSQL cluster.
3. Execute the following queries:

/* only required for major releases, e.g. 1.4 -> 1.5 */
ALTER EXTENSION pg_pathman UPDATE;
SET pg_pathman.enable = t;

Available functions

Module's version

pathman_version()

Although it's possible to get major and minor version numbers using \dx pg_pathman, it doesn't show the actual patch number. This function returns a complete version number of the loaded pg_pathman module in MAJOR.MINOR.PATCH format.

Partition creation

create_hash_partitions(parent_relid     REGCLASS,
                       expression       TEXT,
                       partitions_count INTEGER,
                       partition_data   BOOLEAN DEFAULT TRUE,
                       partition_names  TEXT[] DEFAULT NULL,
                       tablespaces      TEXT[] DEFAULT NULL)

Performs HASH partitioning for relation by partitioning expression expr. The partitions_count parameter specifies the number of partitions to create; it cannot be changed afterwards. If partition_data is true then all the data will be automatically copied from the parent table to partitions. Note that data migration may took a while to finish and the table will be locked until transaction commits. See partition_table_concurrently() for a lock-free way to migrate data. Partition creation callback is invoked for each partition if set beforehand (see set_init_callback()).

create_range_partitions(parent_relid    REGCLASS,
                        expression      TEXT,
                        start_value     ANYELEMENT,
                        p_interval      ANYELEMENT,
                        p_count         INTEGER DEFAULT NULL
                        partition_data  BOOLEAN DEFAULT TRUE)

create_range_partitions(parent_relid    REGCLASS,
                        expression      TEXT,
                        start_value     ANYELEMENT,
                        p_interval      INTERVAL,
                        p_count         INTEGER DEFAULT NULL,
                        partition_data  BOOLEAN DEFAULT TRUE)

create_range_partitions(parent_relid    REGCLASS,
                        expression      TEXT,
                        bounds          ANYARRAY,
                        partition_names TEXT[] DEFAULT NULL,
                        tablespaces     TEXT[] DEFAULT NULL,
                        partition_data  BOOLEAN DEFAULT TRUE)

Performs RANGE partitioning for relation by partitioning expression expr, start_value argument specifies initial value, p_interval sets the default range for auto created partitions or partitions created with append_range_partition() or prepend_range_partition() (if NULL then auto partition creation feature won't work), p_count is the number of premade partitions (if not set then pg_pathman tries to determine it based on expression's values). The bounds array can be built using generate_range_bounds(). Partition creation callback is invoked for each partition if set beforehand.

generate_range_bounds(p_start     ANYELEMENT,
                      p_interval  INTERVAL,
                      p_count     INTEGER)

generate_range_bounds(p_start     ANYELEMENT,
                      p_interval  ANYELEMENT,
                      p_count     INTEGER)

Builds bounds array for create_range_partitions().

Data migration

partition_table_concurrently(relation   REGCLASS,
                             batch_size INTEGER DEFAULT 1000,
                             sleep_time FLOAT8 DEFAULT 1.0)

Starts a background worker to move data from parent table to partitions. The worker utilizes short transactions to copy small batches of data (up to 10K rows per transaction) and thus doesn't significantly interfere with user's activity. If the worker is unable to lock rows of a batch, it sleeps for sleep_time seconds before the next attempt and tries again up to 60 times, and quits if it's still unable to lock the batch.

stop_concurrent_part_task(relation REGCLASS)

Stops a background worker performing a concurrent partitioning task. Note: worker will exit after it finishes relocating a current batch.

Triggers

Triggers are no longer required nor for INSERTs, neither for cross-partition UPDATEs. However, user-supplied triggers are supported:

• Each inserted row results in execution of BEFORE/AFTER INSERT trigger functions of a corresponding partition.
• Each updated row results in execution of BEFORE/AFTER UPDATE trigger functions of a corresponding partition.
• Each moved row (cross-partition update) results in execution of BEFORE UPDATE + BEFORE/AFTER DELETE + BEFORE/AFTER INSERT trigger functions of corresponding partitions.

Post-creation partition management

replace_hash_partition(old_partition REGCLASS,
                       new_partition REGCLASS,
                       lock_parent   BOOLEAN DEFAULT TRUE)

Replaces specified partition of HASH-partitioned table with another table. The lock_parent parameter will prevent any INSERT/UPDATE/ALTER TABLE queries to parent table.

split_range_partition(partition_relid REGCLASS,
                      split_value     ANYELEMENT,
                      partition_name  TEXT DEFAULT NULL,
                      tablespace      TEXT DEFAULT NULL)

Split RANGE partition in two by split_value. Partition creation callback is invoked for a new partition if available.

merge_range_partitions(variadic partitions REGCLASS[])

Merge several adjacent RANGE partitions. Partitions are automatically ordered by increasing bounds; all the data will be accumulated in the first partition.

append_range_partition(parent_relid   REGCLASS,
                       partition_name TEXT DEFAULT NULL,
                       tablespace     TEXT DEFAULT NULL)

Append new RANGE partition with pathman_config.range_interval as interval.

prepend_range_partition(parent_relid   REGCLASS,
                        partition_name TEXT DEFAULT NULL,
                        tablespace     TEXT DEFAULT NULL)

Prepend new RANGE partition with pathman_config.range_interval as interval.

add_range_partition(parent_relid   REGCLASS,
                    start_value    ANYELEMENT,
                    end_value      ANYELEMENT,
                    partition_name TEXT DEFAULT NULL,
                    tablespace     TEXT DEFAULT NULL)

Create new RANGE partition for relation with specified range bounds. If start_value or end_value are NULL then corresponding range bound will be infinite.

drop_range_partition(partition TEXT, delete_data BOOLEAN DEFAULT TRUE)

Drop RANGE partition and all of its data if delete_data is true.

attach_range_partition(parent_relid    REGCLASS,
                       partition_relid REGCLASS,
                       start_value     ANYELEMENT,
                       end_value       ANYELEMENT)

Attach partition to the existing RANGE-partitioned relation. The attached table must have exactly the same structure as the parent table, including the dropped columns. Partition creation callback is invoked if set (see pathman_config_params).

detach_range_partition(partition_relid REGCLASS)

Detach partition from the existing RANGE-partitioned relation.

disable_pathman_for(parent_relid REGCLASS)

Permanently disable pg_pathman partitioning mechanism for the specified parent table and remove the insert trigger if it exists. All partitions and data remain unchanged.

drop_partitions(parent_relid REGCLASS,
                delete_data  BOOLEAN DEFAULT FALSE)

Drop partitions of the parent table (both foreign and local relations). If delete_data is false, the data is copied to the parent table first. Default is false.

To remove partitioned table along with all partitions fully, use conventional DROP TABLE relation CASCADE. However, care should be taken in somewhat rare case when you are running logical replication and DROP was executed by replication apply worker, e.g. via trigger on replicated table. pg_pathman uses pathman_ddl_trigger event trigger to remove the record about dropped table from pathman_config, and this trigger by default won't fire on replica, leading to inconsistent state when pg_pathman thinks that the table still exists, but in fact it doesn't. If this is the case, configure this trigger to fire on replica too:

ALTER EVENT TRIGGER pathman_ddl_trigger ENABLE ALWAYS;

Physical replication doesn't have this problem since DDL as well as pathman_config table is replicated too; master and slave PostgreSQL instances are basically identical, and it is only harmful to keep this trigger in ALWAYS mode.

Additional parameters

set_interval(relation REGCLASS, value ANYELEMENT)

Update RANGE partitioned table interval. Note that interval must not be negative and it must not be trivial, i.e. its value should be greater than zero for numeric types, at least 1 microsecond for TIMESTAMP and at least 1 day for DATE.

set_enable_parent(relation REGCLASS, value BOOLEAN)

Include/exclude parent table into/from query plan. In original PostgreSQL planner parent table is always included into query plan even if it's empty which can lead to additional overhead. You can use disable_parent() if you are never going to use parent table as a storage. Default value depends on the partition_data parameter that was specified during initial partitioning in create_range_partitions() function. If the partition_data parameter was true then all data have already been migrated to partitions and parent table disabled. Otherwise it is enabled.

set_auto(relation REGCLASS, value BOOLEAN)

Enable/disable auto partition propagation (only for RANGE partitioning). It is enabled by default.

set_init_callback(relation REGCLASS, callback REGPROC DEFAULT 0)

Set partition creation callback to be invoked for each attached or created partition (both HASH and RANGE). If callback is marked with SECURITY INVOKER, it's executed with the privileges of the user that produced a statement which has led to creation of a new partition (e.g. INSERT INTO partitioned_table VALUES (-5)). The callback must have the following signature: part_init_callback(args JSONB) RETURNS VOID. Parameter arg consists of several fields whose presence depends on partitioning type:

/* RANGE-partitioned table abc (child abc_4) */
{
    "parent":           "abc",
    "parent_schema":    "public",
    "parttype":         "2",
    "partition":        "abc_4",
    "partition_schema": "public",
    "range_max":        "401",
    "range_min":        "301"
}

/* HASH-partitioned table abc (child abc_0) */
{
    "parent":           "abc",
    "parent_schema":    "public",
    "parttype":         "1",
    "partition":        "abc_0",
    "partition_schema": "public"
}

set_set_spawn_using_bgw(relation REGCLASS, value BOOLEAN)

When INSERTing new data beyond the partitioning range, use SpawnPartitionsWorker to create new partitions in a separate transaction.

Views and tables

pathman_config --- main config storage

CREATE TABLE IF NOT EXISTS pathman_config (
    partrel         REGCLASS NOT NULL PRIMARY KEY,
    expr            TEXT NOT NULL,
    parttype        INTEGER NOT NULL,
    range_interval  TEXT,
    cooked_expr     TEXT);

This table stores a list of partitioned tables.

pathman_config_params --- optional parameters

CREATE TABLE IF NOT EXISTS pathman_config_params (
    partrel         REGCLASS NOT NULL PRIMARY KEY,
    enable_parent   BOOLEAN NOT NULL DEFAULT TRUE,
    auto            BOOLEAN NOT NULL DEFAULT TRUE,
    init_callback   TEXT DEFAULT NULL,
    spawn_using_bgw BOOLEAN NOT NULL DEFAULT FALSE);

This table stores optional parameters which override standard behavior.

pathman_concurrent_part_tasks --- currently running partitioning workers

-- helper SRF function
CREATE OR REPLACE FUNCTION show_concurrent_part_tasks()
RETURNS TABLE (
    userid     REGROLE,
    pid        INT,
    dbid       OID,
    relid      REGCLASS,
    processed  INT,
    status     TEXT)
AS 'pg_pathman', 'show_concurrent_part_tasks_internal'
LANGUAGE C STRICT;

CREATE OR REPLACE VIEW pathman_concurrent_part_tasks
AS SELECT * FROM show_concurrent_part_tasks();

This view lists all currently running concurrent partitioning tasks.

pathman_partition_list --- list of all existing partitions

-- helper SRF function
CREATE OR REPLACE FUNCTION show_partition_list()
RETURNS TABLE (
    parent     REGCLASS,
    partition  REGCLASS,
    parttype   INT4,
    expr       TEXT,
    range_min  TEXT,
    range_max  TEXT)
AS 'pg_pathman', 'show_partition_list_internal'
LANGUAGE C STRICT;

CREATE OR REPLACE VIEW pathman_partition_list
AS SELECT * FROM show_partition_list();

This view lists all existing partitions, as well as their parents and range boundaries (NULL for HASH partitions).

pathman_cache_stats --- per-backend memory consumption

-- helper SRF function
CREATE OR REPLACE FUNCTION @[email protected]_cache_stats()
RETURNS TABLE (
	context     TEXT,
	size        INT8,
	used        INT8,
	entries     INT8)
AS 'pg_pathman', 'show_cache_stats_internal'
LANGUAGE C STRICT;

CREATE OR REPLACE VIEW @[email protected]_cache_stats
AS SELECT * FROM @[email protected]_cache_stats();

Shows memory consumption of various caches.

Declarative partitioning

From PostgreSQL 10 ATTACH PARTITION, DETACH PARTITION and CREATE TABLE .. PARTITION OF commands could be used with tables partitioned by pg_pathman:

CREATE TABLE child1 (LIKE partitioned_table);

--- attach new partition
ALTER TABLE partitioned_table ATTACH PARTITION child1
	FOR VALUES FROM ('2015-05-01') TO ('2015-06-01');

--- detach the partition
ALTER TABLE partitioned_table DETACH PARTITION child1;

-- create a partition
CREATE TABLE child2 PARTITION OF partitioned_table
	FOR VALUES IN ('2015-05-01', '2015-06-01');

Custom plan nodes

pg_pathman provides a couple of custom plan nodes which aim to reduce execution time, namely:

• RuntimeAppend (overrides Append plan node)
• RuntimeMergeAppend (overrides MergeAppend plan node)
• PartitionFilter (drop-in replacement for INSERT triggers)
• PartitionOverseer (implements cross-partition UPDATEs)
• PartitionRouter (implements cross-partition UPDATEs)

PartitionFilter acts as a proxy node for INSERT's child scan, which means it can redirect output tuples to the corresponding partition:

EXPLAIN (COSTS OFF)
INSERT INTO partitioned_table
SELECT generate_series(1, 10), random();
               QUERY PLAN
-----------------------------------------
 Insert on partitioned_table
   ->  Custom Scan (PartitionFilter)
         ->  Subquery Scan on "*SELECT*"
               ->  Result
(4 rows)

PartitionOverseer and PartitionRouter are another proxy nodes used in conjunction with PartitionFilter to enable cross-partition UPDATEs (i.e. when update of partitioning key requires that we move row to another partition). Since this node has a great deal of side effects (ordinary UPDATE becomes slower; cross-partition UPDATE is transformed into DELETE + INSERT), it is disabled by default. To enable it, refer to the list of GUCs below.

EXPLAIN (COSTS OFF)
UPDATE partitioned_table
SET value = value + 1 WHERE value = 2;
                       QUERY PLAN
---------------------------------------------------------
 Custom Scan (PartitionOverseer)
   ->  Update on partitioned_table_2
         ->  Custom Scan (PartitionFilter)
               ->  Custom Scan (PartitionRouter)
                     ->  Seq Scan on partitioned_table_2
                           Filter: (value = 2)
(6 rows)

RuntimeAppend and RuntimeMergeAppend have much in common: they come in handy in a case when WHERE condition takes form of:

VARIABLE OP PARAM

This kind of expressions can no longer be optimized at planning time since the parameter's value is not known until the execution stage takes place. The problem can be solved by embedding the WHERE condition analysis routine into the original Append's code, thus making it pick only required scans out of a whole bunch of planned partition scans. This effectively boils down to creation of a custom node capable of performing such a check.

---

There are at least several cases that demonstrate usefulness of these nodes:

/* create table we're going to partition */
CREATE TABLE partitioned_table(id INT NOT NULL, payload REAL);

/* insert some data */
INSERT INTO partitioned_table
SELECT generate_series(1, 1000), random();

/* perform partitioning */
SELECT create_hash_partitions('partitioned_table', 'id', 100);

/* create ordinary table */
CREATE TABLE some_table AS SELECT generate_series(1, 100) AS VAL;

• id = (select ... limit 1)

EXPLAIN (COSTS OFF, ANALYZE) SELECT * FROM partitioned_table
WHERE id = (SELECT * FROM some_table LIMIT 1);
                                             QUERY PLAN
----------------------------------------------------------------------------------------------------
 Custom Scan (RuntimeAppend) (actual time=0.030..0.033 rows=1 loops=1)
   InitPlan 1 (returns $0)
     ->  Limit (actual time=0.011..0.011 rows=1 loops=1)
           ->  Seq Scan on some_table (actual time=0.010..0.010 rows=1 loops=1)
   ->  Seq Scan on partitioned_table_70 partitioned_table (actual time=0.004..0.006 rows=1 loops=1)
         Filter: (id = $0)
         Rows Removed by Filter: 9
 Planning time: 1.131 ms
 Execution time: 0.075 ms
(9 rows)

/* disable RuntimeAppend node */
SET pg_pathman.enable_runtimeappend = f;

EXPLAIN (COSTS OFF, ANALYZE) SELECT * FROM partitioned_table
WHERE id = (SELECT * FROM some_table LIMIT 1);
                                    QUERY PLAN
----------------------------------------------------------------------------------
 Append (actual time=0.196..0.274 rows=1 loops=1)
   InitPlan 1 (returns $0)
     ->  Limit (actual time=0.005..0.005 rows=1 loops=1)
           ->  Seq Scan on some_table (actual time=0.003..0.003 rows=1 loops=1)
   ->  Seq Scan on partitioned_table_0 (actual time=0.014..0.014 rows=0 loops=1)
         Filter: (id = $0)
         Rows Removed by Filter: 6
   ->  Seq Scan on partitioned_table_1 (actual time=0.003..0.003 rows=0 loops=1)
         Filter: (id = $0)
         Rows Removed by Filter: 5
         ... /* more plans follow */
 Planning time: 1.140 ms
 Execution time: 0.855 ms
(306 rows)

• id = ANY (select ...)

EXPLAIN (COSTS OFF, ANALYZE) SELECT * FROM partitioned_table
WHERE id = any (SELECT * FROM some_table limit 4);
                                                QUERY PLAN
-----------------------------------------------------------------------------------------------------------
 Nested Loop (actual time=0.025..0.060 rows=4 loops=1)
   ->  Limit (actual time=0.009..0.011 rows=4 loops=1)
         ->  Seq Scan on some_table (actual time=0.008..0.010 rows=4 loops=1)
   ->  Custom Scan (RuntimeAppend) (actual time=0.002..0.004 rows=1 loops=4)
         ->  Seq Scan on partitioned_table_70 partitioned_table (actual time=0.001..0.001 rows=10 loops=1)
         ->  Seq Scan on partitioned_table_26 partitioned_table (actual time=0.002..0.003 rows=9 loops=1)
         ->  Seq Scan on partitioned_table_27 partitioned_table (actual time=0.001..0.002 rows=20 loops=1)
         ->  Seq Scan on partitioned_table_63 partitioned_table (actual time=0.001..0.002 rows=9 loops=1)
 Planning time: 0.771 ms
 Execution time: 0.101 ms
(10 rows)

/* disable RuntimeAppend node */
SET pg_pathman.enable_runtimeappend = f;

EXPLAIN (COSTS OFF, ANALYZE) SELECT * FROM partitioned_table
WHERE id = any (SELECT * FROM some_table limit 4);
                                       QUERY PLAN
-----------------------------------------------------------------------------------------
 Nested Loop Semi Join (actual time=0.531..1.526 rows=4 loops=1)
   Join Filter: (partitioned_table.id = some_table.val)
   Rows Removed by Join Filter: 3990
   ->  Append (actual time=0.190..0.470 rows=1000 loops=1)
         ->  Seq Scan on partitioned_table (actual time=0.187..0.187 rows=0 loops=1)
         ->  Seq Scan on partitioned_table_0 (actual time=0.002..0.004 rows=6 loops=1)
         ->  Seq Scan on partitioned_table_1 (actual time=0.001..0.001 rows=5 loops=1)
         ->  Seq Scan on partitioned_table_2 (actual time=0.002..0.004 rows=14 loops=1)
... /* 96 scans follow */
   ->  Materialize (actual time=0.000..0.000 rows=4 loops=1000)
         ->  Limit (actual time=0.005..0.006 rows=4 loops=1)
               ->  Seq Scan on some_table (actual time=0.003..0.004 rows=4 loops=1)
 Planning time: 2.169 ms
 Execution time: 2.059 ms
(110 rows)

• NestLoop involving a partitioned table, which is omitted since it's occasionally shown above.

---

In case you're interested, you can read more about custom nodes at Alexander Korotkov's blog.

Examples

Common tips

• You can easily add partition column containing the names of the underlying partitions using the system attribute called tableoid:

SELECT tableoid::regclass AS partition, * FROM partitioned_table;

• Though indices on a parent table aren't particularly useful (since it's supposed to be empty), they act as prototypes for indices on partitions. For each index on the parent table, pg_pathman will create a similar index on every partition.

• All running concurrent partitioning tasks can be listed using the pathman_concurrent_part_tasks view:

SELECT * FROM pathman_concurrent_part_tasks;
 userid | pid  | dbid  | relid | processed | status
--------+------+-------+-------+-----------+---------
 dmitry | 7367 | 16384 | test  |    472000 | working
(1 row)

• pathman_partition_list in conjunction with drop_range_partition() can be used to drop RANGE partitions in a more flexible way compared to good old DROP TABLE:

SELECT drop_range_partition(partition, false) /* move data to parent */
FROM pathman_partition_list
WHERE parent = 'part_test'::regclass AND range_min::int < 500;
NOTICE:  1 rows copied from part_test_11
NOTICE:  100 rows copied from part_test_1
NOTICE:  100 rows copied from part_test_2
 drop_range_partition
----------------------
 dummy_test_11
 dummy_test_1
 dummy_test_2
(3 rows)

• You can turn foreign tables into partitions using the attach_range_partition() function. Rows that were meant to be inserted into parent will be redirected to foreign partitions (as usual, PartitionFilter will be involved), though by default it is prohibited to insert rows into partitions provided not by postgres_fdw. Only superuser is allowed to set pg_pathman.insert_into_fdw GUC variable.

HASH partitioning

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

CREATE TABLE items (
    id       SERIAL PRIMARY KEY,
    name     TEXT,
    code     BIGINT);

INSERT INTO items (id, name, code)
SELECT g, md5(g::text), random() * 100000
FROM generate_series(1, 100000) as g;

Now run the create_hash_partitions() function with appropriate arguments:

SELECT create_hash_partitions('items', 'id', 100);

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

Here's an example of the query performing filtering by partitioning key:

SELECT * FROM items WHERE id = 1234;
  id  |               name               | code
------+----------------------------------+------
 1234 | 81dc9bdb52d04dc20036dbd8313ed055 | 1855
(1 row)

EXPLAIN SELECT * FROM items WHERE id = 1234;
                                     QUERY PLAN
------------------------------------------------------------------------------------
 Append  (cost=0.28..8.29 rows=0 width=0)
   ->  Index Scan using items_34_pkey on items_34  (cost=0.28..8.29 rows=0 width=0)
         Index Cond: (id = 1234)

Notice that the Append node contains only one child scan which corresponds to the WHERE clause.

Important: pay attention to the fact that pg_pathman excludes the parent table from the query plan.

To access parent table use ONLY modifier:

EXPLAIN SELECT * FROM ONLY items;
                      QUERY PLAN
------------------------------------------------------
 Seq Scan on items  (cost=0.00..0.00 rows=1 width=45)

RANGE partitioning

Consider an example of RANGE partitioning. Let's create a table containing some dummy logs:

CREATE TABLE journal (
    id      SERIAL,
    dt      TIMESTAMP NOT NULL,
    level   INTEGER,
    msg     TEXT);

-- similar index will also be created for each partition
CREATE INDEX ON journal(dt);

-- generate some data
INSERT INTO journal (dt, level, msg)
SELECT g, random() * 6, md5(g::text)
FROM generate_series('2015-01-01'::date, '2015-12-31'::date, '1 minute') as g;

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

SELECT create_range_partitions('journal', 'dt', '2015-01-01'::date, '1 day'::interval);

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:

-- add new partition with specified range
SELECT add_range_partition('journal', '2016-01-01'::date, '2016-01-07'::date);

-- append new partition with default range
SELECT append_range_partition('journal');

The first one creates a partition with specified range. The second one creates a 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 some outdated data:

CREATE FOREIGN TABLE journal_archive (
    id      INTEGER NOT NULL,
    dt      TIMESTAMP NOT NULL,
    level   INTEGER,
    msg     TEXT)
SERVER archive_server;

SELECT attach_range_partition('journal', 'journal_archive', '2014-01-01'::date, '2015-01-01'::date);

Important: the definition of the attached table must match the one of the existing partitioned table, including the dropped columns.

To merge to adjacent partitions, use the merge_range_partitions() function:

SELECT merge_range_partitions('journal_archive', 'journal_1');

To split partition by value, use the split_range_partition() function:

SELECT split_range_partition('journal_366', '2016-01-03'::date);

To detach partition, use the detach_range_partition() function:

SELECT detach_range_partition('journal_archive');

Here's an example of the query performing filtering by partitioning key:

SELECT * FROM journal WHERE dt >= '2015-06-01' AND dt < '2015-06-03';
   id   |         dt          | level |               msg
--------+---------------------+-------+----------------------------------
 217441 | 2015-06-01 00:00:00 |     2 | 15053892d993ce19f580a128f87e3dbf
 217442 | 2015-06-01 00:01:00 |     1 | 3a7c46f18a952d62ce5418ac2056010c
 217443 | 2015-06-01 00:02:00 |     0 | 92c8de8f82faf0b139a3d99f2792311d
 ...
(2880 rows)

EXPLAIN SELECT * FROM journal WHERE dt >= '2015-06-01' AND dt < '2015-06-03';
                            QUERY PLAN
------------------------------------------------------------------
 Append  (cost=0.00..58.80 rows=0 width=0)
   ->  Seq Scan on journal_152  (cost=0.00..29.40 rows=0 width=0)
   ->  Seq Scan on journal_153  (cost=0.00..29.40 rows=0 width=0)
(3 rows)

Disabling pg_pathman

There are several user-accessible GUC variables designed to toggle the whole module or specific custom nodes on and off:

• pg_pathman.enable --- disable (or enable) pg_pathman completely
• pg_pathman.enable_runtimeappend --- toggle RuntimeAppend custom node on\off
• pg_pathman.enable_runtimemergeappend --- toggle RuntimeMergeAppend custom node on\off
• pg_pathman.enable_partitionfilter --- toggle PartitionFilter custom node on\off (for INSERTs)
• pg_pathman.enable_partitionrouter --- toggle PartitionRouter custom node on\off (for cross-partition UPDATEs)
• pg_pathman.enable_auto_partition --- toggle automatic partition creation on\off (per session)
• pg_pathman.enable_bounds_cache --- toggle bounds cache on\off (faster updates of partitioning scheme)
• pg_pathman.insert_into_fdw --- allow INSERTs into various FDWs (disabled | postgres | any_fdw)
• pg_pathman.override_copy --- toggle COPY statement hooking on\off

To permanently disable pg_pathman for some previously partitioned table, use the disable_pathman_for() function:

SELECT disable_pathman_for('range_rel');

All sections and data will remain unchanged and will be handled by the standard PostgreSQL inheritance mechanism.

Feedback

Do not hesitate to post your issues, questions and new ideas at the issues page.

Authors

Ildar Musin Alexander Korotkov <a.korotkov(at)postgrespro.ru> Postgres Professional Ltd., Russia Dmitry Ivanov Maksim Milyutin <m.milyutin(at)postgrespro.ru> Postgres Professional Ltd., Russia Ildus Kurbangaliev