Pgslice: Postgres partitioning as easy as pie

Postgres partitioning as easy as pie. Works great for both new and existing tables, with zero downtime and minimal app changes.

🍊 Battle-tested at Instacart

Install

Run:

Steps

1. Ensure the table you want to partition has been created. We’ll refer to this as <table>.

2. Specify your database credentials

   export PGSLICE_URL=postgres://localhost/myapp_development

3. Create an intermediate table

   pgslice prep <table><column><period>

   Period can be day or month.

   This creates a table named <table>_intermediate with the appropriate trigger for partitioning.

4. Add partitions

   pgslice add_partitions <table> --intermediate --past 3 --future 3

   This creates child tables that inherit from the intermediate table.

   Use the --past and --future options to control the number of partitions.

5. Optional, for tables with data - Fill the partitions in batches with data from the original table

   Use the --batch-size and --sleep options to control the speed.

   To sync data across different databases, check out pgsync.

6. Swap the intermediate table with the original table

   The original table is renamed <table>_retired and the intermediate table is renamed <table>.

7. Fill the rest (rows inserted between the first fill and the swap)

   pgslice fill <table> --swapped

8. Archive and drop the original table

Adding Partitions

To add partitions, use:

pgslice add_partitions <table> --future 3

Add this as a cron job to create a new partition each day or month.

# day
0 0 *** pgslice add_partitions <table> --future 3 --url ...# month
0 0 1 ** pgslice add_partitions <table> --future 3 --url ...

Add a monitor to ensure partitions are being created.

SELECT1FROMpg_catalog.pg_class cINNER JOINpg_catalog.pg_namespace n ONn.oid=c.relnamespaceWHEREc.relkind='r'ANDn.nspname='public'ANDc.relname='<table>_'|| to_char(NOW() + INTERVAL '3 days', 'YYYYMMDD')-- for months, use to_char(NOW() + INTERVAL '3 months', 'YYYYMM')

Additional Commands

To undo prep (which will delete partitions), use:

To undo swap, use:

Sample Output

pgslice prints the SQL commands that were executed on the server. To print without executing, use the --dry-run option.

$ pgslice prep locations created_at dayBEGIN;CREATE TABLE locations_intermediate (LIKE locations INCLUDING ALL);CREATE FUNCTION locations_insert_trigger()    RETURNS trigger AS $$    BEGIN        EXECUTE 'INSERT INTO locations_' || to_char(NEW.created_at, 'YYYYMMDD') || ' VALUES ($1.*)' USING NEW;        RETURN NULL;    END;    $$ LANGUAGE plpgsql;CREATE TRIGGER locations_insert_trigger    BEFORE INSERT ON locations_intermediate    FOR EACH ROW EXECUTE PROCEDURE locations_insert_trigger();COMMIT;

$ pgslice add_partitions locations --intermediate --past 1 --future 1BEGIN;CREATE TABLE locations_20160423    (CHECK (created_at >= '2016-04-23'::date AND created_at < '2016-04-24'::date))    INHERITS (locations_intermediate);ALTER TABLE locations_20160423 ADD PRIMARY KEY (id);CREATE INDEX ON locations_20160423 USING btree (shopper_id);CREATE TABLE locations_20160424    (CHECK (created_at >= '2016-04-24'::date AND created_at < '2016-04-25'::date))    INHERITS (locations_intermediate);ALTER TABLE locations_20160424 ADD PRIMARY KEY (id);CREATE INDEX ON locations_20160424 USING btree (shopper_id);CREATE TABLE locations_20160425    (CHECK (created_at >= '2016-04-25'::date AND created_at < '2016-04-26'::date))    INHERITS (locations_intermediate);ALTER TABLE locations_20160425 ADD PRIMARY KEY (id);CREATE INDEX ON locations_20160425 USING btree (shopper_id);COMMIT;

$ pgslice fill locations/* 1 of 3 */INSERT INTO locations_intermediate (id, latitude, longitude, created_at)    SELECT id, latitude, longitude, created_at FROM locations    WHERE id > 0 AND id <= 10000 AND created_at >= '2016-04-23'::date AND created_at < '2016-04-26'::date/* 2 of 3 */INSERT INTO locations_intermediate (id, latitude, longitude, created_at)    SELECT id, latitude, longitude, created_at FROM locations    WHERE id > 10000 AND id <= 20000 AND created_at >= '2016-04-23'::date AND created_at < '2016-04-26'::date/* 3 of 3 */INSERT INTO locations_intermediate (id, latitude, longitude, created_at)    SELECT id, latitude, longitude, created_at FROM locations    WHERE id > 20000 AND id <= 30000 AND created_at >= '2016-04-23'::date AND created_at < '2016-04-26'::date

$ pgslice swap locationsBEGIN;ALTER TABLE locations RENAME TO locations_retired;ALTER TABLE locations_intermediate RENAME TO locations;ALTER SEQUENCE locations_id_seq OWNED BY locations.id;COMMIT;

$ pgslice add_partitions locations --future 2BEGIN;CREATE TABLE locations_20160426    (CHECK (created_at >= '2016-04-26'::date AND created_at < '2016-04-27'::date))    INHERITS (locations);ALTER TABLE locations_20160426 ADD PRIMARY KEY (id);CREATE INDEX ON locations_20160426 USING btree (shopper_id);COMMIT;

App Changes

This set up allows you to read and write with the original table name with no knowledge it’s partitioned. However, there are a few things to be aware of.

Reads

When possible, queries should include the column you partition on to limit the number of partitions the database needs to check. For instance, if you partition on created_at, try to include it in queries:

SELECT*FROM
    some_tableWHERE
    some_column =123AND-- for performance only
    created_at >='2016-01-01'AND created_at <'2016-01-02'

For this to be effective, ensure constraint_exclusion is set to partition (default value) or on.

SHOW constraint_exclusion;

Writes

If you use INSERT statements with a RETURNING clause (as frameworks like Rails do), you’ll no longer receive the id of the newly inserted record back. If you need this, you can either:

1. Insert directly into the partition
2. Get the value after the insert with SELECT CURRVAL('sequence_name')

One Off Tasks

You can also use pgslice to reduce the size of a table without partitioning by creating a new table, filling it with a subset of records, and swapping it in.

pgslice prep <table> --no-partition
pgslice fill <table> --start 1000 # starting primary key
pgslice swap <table>

Upgrading

Run:

To use master, run:

gem install specific_install
gem specific_install ankane/pgslice

Reference

TODO

• Command to sync index changes with partitions
• Disable indexing for faster fill
• ETA for fill

Contributing

Everyone is encouraged to help improve this project. Here are a few ways you can help: