Postgres partitioning as easy as pie. Works great for both new and existing tables, with zero downtime and minimal app changes. No need to install anything on your database server. 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://localhost/myapp_development
- Create an intermediate table
pgslice prep <table> <column> <period>
Period can be day
, month
, or year
.
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.
- Analyze tables
pgslice analyze <table>
- 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 "public"."visits_intermediate" (LIKE "public"."visits" INCLUDING DEFAULTS INCLUDING CONSTRAINTS INCLUDING STORAGE INCLUDING COMMENTS) PARTITION BY RANGE ("created_at");
CREATE INDEX ON "public"."visits_intermediate" USING btree ("created_at");
COMMENT ON TABLE "public"."visits_intermediate" is 'column:createdAt,period:day,cast:date,version:3';
COMMIT;
pgslice add_partitions visits --intermediate --past 1 --future 1
BEGIN;
CREATE TABLE "public"."visits_201808" PARTITION OF "public"."visits_intermediate" FOR VALUES FROM ('2018-08-01') TO ('2018-09-01');
ALTER TABLE "public"."visits_201808" ADD PRIMARY KEY ("id");
CREATE TABLE "public"."visits_201809" PARTITION OF "public"."visits_intermediate" FOR VALUES FROM ('2018-09-01') TO ('2018-10-01');
ALTER TABLE "public"."visits_201809" ADD PRIMARY KEY ("id");
CREATE TABLE "public"."visits_201810" PARTITION OF "public"."visits_intermediate" FOR VALUES FROM ('2018-10-01') TO ('2018-11-01');
ALTER TABLE "public"."visits_201808" ADD PRIMARY KEY ("id");
COMMIT;
pgslice fill visits
/* 1 of 3 */
INSERT INTO "public"."visits_intermediate" ("id", "user_id", "ip", "created_at")
SELECT "id", "user_id", "ip", "created_at" FROM "public"."visits"
WHERE "id" > 0 AND "id" <= 10000 AND "created_at" >= '2018-08-01'::date AND "created_at" < '2018-11-01'::date
/* 2 of 3 */
INSERT INTO "public"."visits_intermediate" ("id", "user_id", "ip", "created_at")
SELECT "id", "user_id", "ip", "created_at" FROM "public"."visits"
WHERE "id" > 10000 AND "id" <= 20000 AND "created_at" >= '2018-08-01'::date AND "created_at" < '2018-11-01'::date
/* 3 of 3 */
INSERT INTO "public"."visits_intermediate" ("id", "user_id", "ip", "created_at")
SELECT "id", "user_id", "ip", "created_at" FROM "public"."visits"
WHERE "id" > 20000 AND "id" <= 30000 AND "created_at" >= '2018-08-01'::date AND "created_at" < '2018-11-01'::date
pgslice analyze visits
ANALYZE VERBOSE "public"."visits_201808";
ANALYZE VERBOSE "public"."visits_201809";
ANALYZE VERBOSE "public"."visits_201810";
ANALYZE VERBOSE "public"."visits_intermediate";
pgslice swap visits
BEGIN;
SET LOCAL lock_timeout = '5s';
ALTER TABLE "public"."visits" RENAME TO "visits_retired";
ALTER TABLE "public"."visits_intermediate" RENAME TO "visits";
ALTER SEQUENCE "visits_id_seq" OWNED BY "public"."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, month, or year.
# day
0 0 * * * pgslice add_partitions <table> --future 3 --url ...
# month
0 0 1 * * pgslice add_partitions <table> --future 3 --url ...
# year
0 0 1 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')
-- for years, use to_char(NOW() + INTERVAL '3 years', 'YYYY')
Back up and drop older partitions each day, month, or year.
pg_dump -c -Fc -t <table>_201809 $PGSLICE_URL > <table>_201809.dump
psql -c "DROP <table>_201809" $PGSLICE_URL
If you use Amazon S3 for backups, s3cmd is a nice tool.
s3cmd put <table>_201809.dump s3://<s3-bucket>/<table>_201809.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 >= '2018-09-01' AND created_at < '2018-09-02'
For this to be effective, ensure constraint_exclusion
is set to partition
(default value) or on
.
SHOW constraint_exclusion;
Before Postgres 10, 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(s) back. If you need this, you can either:
- Insert directly into the partition
- Get value before the insert with
SELECT nextval('sequence_name')
(for multiple rows, appendFROM generate_series(1, n)
)
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>
Once a table is partitioned, here’s how to change the schema:
- To add, remove, or modify a column, make the update on the master table only.
- To add or remove an index or foreign key, make the update on the master table. For Postgres < 11, make the update on all partitions as well.
Postgres 10 introduces declarative partitioning. A major benefit is INSERT
statements with a RETURNING
clause work as expected. If you prefer to use trigger-based partitioning instead (not recommended), pass the --trigger-based
option to the prep
command.
Always make sure your connection is secure when connecting to your database over a network you don’t fully trust. Your best option is to connect over SSH or a VPN. Another option is to use sslmode=verify-full
. If you don’t do this, your database credentials can be compromised.
Run:
gem install pgslice
To use master, run:
gem install specific_install
gem specific_install https://github.com/ankane/pgslice.git
docker build -t pgslice .
alias pgslice="docker run --rm -e PGSLICE_URL pgslice"
This will give you the pgslice
command.
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
To run tests, do:
git clone https://github.com/ankane/pgslice.git
cd pgslice
bundle install
createdb pgslice_test
bundle exec rake
To test against different versions of Postgres with Docker, use:
docker run -p=8000:5432 postgres:10
TZ=Etc/UTC PGSLICE_URL=postgres://postgres@localhost:8000/postgres bundle exec rake
On Mac, you must use Docker for Mac for the port mapping to localhost to work.