Postgres partitioning as easy as pie. Works great for both new and existing tables, with zero downtime and minimal app changes. Archive older data on a rolling basis to keep your database size under control.
🍊 Battle-tested at Instacart
pgslice is a command line tool. To install, run:
gem install pgslice
This will give you the pgslice
command.
-
Ensure the table you want to partition has been created. We’ll refer to this as
<table>
. -
Specify your database credentials
export PGSLICE_URL=postgres:https://localhost/myapp_development
- 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.
- 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.
- Optional, for tables with data - Fill the partitions in batches with data from the original table
pgslice fill <table>
Use the --batch-size
and --sleep
options to control the speed.
To sync data across different databases, check out pgsync.
- Swap the intermediate table with the original table
pgslice swap <table>
The original table is renamed <table>_retired
and the intermediate table is renamed <table>
.
- Fill the rest (rows inserted between the first fill and the swap)
pgslice fill <table> --swapped
- Back up the retired table with a tool like pg_dump and drop it
pg_dump -c -Fc -t <table>_retired $PGSLICE_URL > <table>_retired.dump
psql -c "DROP <table>_retired" $PGSLICE_URL
pgslice prints the SQL commands that were executed on the server. To print without executing, use the --dry-run
option.
pgslice prep visits created_at month
BEGIN;
CREATE TABLE visits_intermediate (LIKE visits INCLUDING ALL);
CREATE FUNCTION visits_insert_trigger()
RETURNS trigger AS $$
BEGIN
RAISE EXCEPTION 'Create partitions first.';
END;
$$ LANGUAGE plpgsql;
CREATE TRIGGER visits_insert_trigger
BEFORE INSERT ON visits_intermediate
FOR EACH ROW EXECUTE PROCEDURE visits_insert_trigger();
COMMENT ON TRIGGER visits_insert_trigger ON visits_intermediate is 'column:created_at,period:month';
COMMIT;
pgslice add_partitions visits --intermediate --past 1 --future 1
BEGIN;
CREATE TABLE visits_201608
(CHECK (created_at >= '2016-08-01'::date AND created_at < '2016-09-01'::date))
INHERITS (visits_intermediate);
ALTER TABLE visits_201608 ADD PRIMARY KEY (id);
CREATE INDEX ON visits_201608 USING btree (user_id);
CREATE TABLE visits_201609
(CHECK (created_at >= '2016-09-01'::date AND created_at < '2016-10-01'::date))
INHERITS (visits_intermediate);
ALTER TABLE visits_201609 ADD PRIMARY KEY (id);
CREATE INDEX ON visits_201609 USING btree (user_id);
CREATE TABLE visits_201610
(CHECK (created_at >= '2016-10-01'::date AND created_at < '2016-11-01'::date))
INHERITS (visits_intermediate);
ALTER TABLE visits_201610 ADD PRIMARY KEY (id);
CREATE INDEX ON visits_201610 USING btree (user_id);
CREATE OR REPLACE FUNCTION visits_insert_trigger()
RETURNS trigger AS $$
BEGIN
IF (NEW.created_at >= '2016-09-01'::date AND NEW.created_at < '2016-10-01'::date) THEN
INSERT INTO visits_201609 VALUES (NEW.*);
ELSIF (NEW.created_at >= '2016-10-01'::date AND NEW.created_at < '2016-11-01'::date) THEN
INSERT INTO visits_201610 VALUES (NEW.*);
ELSIF (NEW.created_at >= '2016-08-01'::date AND NEW.created_at < '2016-09-01'::date) THEN
INSERT INTO visits_201608 VALUES (NEW.*);
ELSE
RAISE EXCEPTION 'Date out of range. Ensure partitions are created.';
END IF;
RETURN NULL;
END;
$$ LANGUAGE plpgsql;
COMMIT;
pgslice fill visits
/* 1 of 3 */
INSERT INTO visits_intermediate ("id", "user_id", "ip", "created_at")
SELECT "id", "user_id", "ip", "created_at" FROM visits
WHERE id > 0 AND id <= 10000 AND created_at >= '2016-08-01'::date AND created_at < '2016-11-01'::date
/* 2 of 3 */
INSERT INTO visits_intermediate ("id", "user_id", "ip", "created_at")
SELECT "id", "user_id", "ip", "created_at" FROM visits
WHERE id > 10000 AND id <= 20000 AND created_at >= '2016-08-01'::date AND created_at < '2016-11-01'::date
/* 3 of 3 */
INSERT INTO visits_intermediate ("id", "user_id", "ip", "created_at")
SELECT "id", "user_id", "ip", "created_at" FROM visits
WHERE id > 20000 AND id <= 30000 AND created_at >= '2016-08-01'::date AND created_at < '2016-11-01'::date
pgslice swap visits
BEGIN;
SET LOCAL lock_timeout = '5s';
ALTER TABLE visits RENAME TO visits_retired;
ALTER TABLE visits_intermediate RENAME TO visits;
ALTER SEQUENCE visits_id_seq OWNED BY visits.id;
COMMIT;
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.
SELECT 1 FROM
pg_catalog.pg_class c
INNER JOIN
pg_catalog.pg_namespace n ON n.oid = c.relnamespace
WHERE
c.relkind = 'r' AND
n.nspname = 'public' AND
c.relname = '<table>_' || to_char(NOW() + INTERVAL '3 days', 'YYYYMMDD')
-- for months, use to_char(NOW() + INTERVAL '3 months', 'YYYYMM')
Back up and drop older partitions each day or month.
pg_dump -c -Fc -t <table>_201609 $PGSLICE_URL > <table>_201609.dump
psql -c "DROP <table>_201609" $PGSLICE_URL
If you use Amazon S3 for backups, s3cmd is a nice tool.
s3cmd put <table>_201609.dump s3:https://<s3-bucket>/<table>_201609.dump
To undo prep (which will delete partitions), use:
pgslice unprep <table>
To undo swap, use:
pgslice unswap <table>
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.
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
visits
WHERE
user_id = 123 AND
-- for performance
created_at >= '2016-09-01' AND created_at < '2016-09-02'
For this to be effective, ensure constraint_exclusion
is set to partition
(default value) or on
.
SHOW constraint_exclusion;
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:
- Insert directly into the partition
- Get the value after the insert with
SELECT CURRVAL('sequence_name')
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> --where "id > 1000" # use any conditions
pgslice swap <table>
Run:
gem install pgslice
To use master, run:
gem install specific_install
gem specific_install ankane/pgslice
docker build -t pgslice .
alias pgslice="docker run --rm -e PGSLICE_URL pgslice"
This will give you the pgslice
command.
- Command to sync index changes with partitions
- Disable indexing for faster
fill
- ETA for
fill
Also check out:
Everyone is encouraged to help improve this project. Here are a few ways you can help:
- Report bugs
- Fix bugs and submit pull requests
- Write, clarify, or fix documentation
- Suggest or add new features