pgx_ulid

A postgres extension to support ulid.

1. Why should I use this?
2. Why should I use ulid over uuid?
3. Monotonicity
4. Usage
5. Installation
6. Troubleshooting

Why should I use this?

There are several different postgres extensions for ulid, but all of them have feature gaps. A good extension should have:

• Generator: A generator function to generate ulid identifiers.
• Binary: Data be stored as binary and not text.
• Type: A postgres type ulid which is displayed as ulid text.
• Uuid: Support for casting between UUID and ulid
• Timestamp: Support to cast an ulid to a timestamp
• Monotonic: Support monotonicity

Name	Language	Generator	Binary	Type	UUID	Timestamp	Monotonic
pgx_ulid	Rust	✔️	✔️	✔️	✔️	✔️	✔️
pgulid	PL/pgSQL	✔️	❌	❌	❌	❌	❌
pg_idkit	Rust	✔️	❌	❌	❌	❌	❌
uids-postgres	Rust	✔️	⁉️1	❌	⁉️2	❌	❌
pgsql_ulid	PL/pgSQL	❌	⁉️1	❌	✔️	❌	❌
pg-ulid	C	✔️	❌	❌	❌	❌	❌
ulid-postgres	PL/pgSQL	✔️	❌	✔️	❌	✔️	❌
pg_ulid	Go	✔️	❌	❌	❌	✔️	❌
pg_ulid	C++	✔️	⁉️1	❌	✔️	❌	❌

Why should I use ulid over uuid?

The main advantages are:

• Indexes created over ULIDs are less fragmented compared to UUIDs due to the timestamp and monotonicity that was encoded in the ULID when it was created.
• ULIDs don't use special characters, so they can be used in URLs or even HTML.
• ULIDs are shorter than UUIDs as they are comprised of 26 characters compared to UUIDs' 36 characters.

This extension is approximately 30% faster than both pgcrypto's UUID and pg_uuidv7's UUIDv7 when generating a million identifiers.

ulid=# EXPLAIN ANALYSE SELECT gen_random_uuid() FROM generate_series(1, 1000000);
                                                            QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------
 Function Scan on generate_series  (cost=0.00..12500.00 rows=1000000 width=16) (actual time=46.630..1401.638 rows=1000000 loops=1)
 Planning Time: 0.020 ms
 Execution Time: 1430.364 ms
(3 rows)

ulid=# EXPLAIN ANALYSE SELECT uuid_generate_v7() FROM generate_series(1, 1000000);
                                                            QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------
 Function Scan on generate_series  (cost=0.00..12500.00 rows=1000000 width=16) (actual time=46.977..1427.477 rows=1000000 loops=1)
 Planning Time: 0.031 ms
 Execution Time: 1456.333 ms
(3 rows)

ulid=# EXPLAIN ANALYSE SELECT gen_ulid() FROM generate_series(1, 1000000);
                                                            QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------
 Function Scan on generate_series  (cost=0.00..12500.00 rows=1000000 width=32) (actual time=46.820..1070.447 rows=1000000 loops=1)
 Planning Time: 0.020 ms
 Execution Time: 1098.086 ms
(3 rows)

This extension is approximately 20% faster than both pgcrypto's UUID and pg_uuidv7's UUIDv7 when generating and inserting a million identifiers.

ulid=# EXPLAIN ANALYSE INSERT INTO uuid_keys(id) SELECT gen_random_uuid() FROM generate_series(1, 1000000);
                                                               QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------------
 Insert on uuid_keys  (cost=0.00..22500.00 rows=0 width=0) (actual time=2006.633..2006.634 rows=0 loops=1)
   ->  Function Scan on generate_series  (cost=0.00..12500.00 rows=1000000 width=16) (actual time=46.846..1459.869 rows=1000000 loops=1)
 Planning Time: 0.029 ms
 Execution Time: 2008.195 ms
(4 rows)

ulid=# EXPLAIN ANALYSE INSERT INTO uuid7_keys(id) SELECT uuid_generate_v7() FROM generate_series(1, 1000000);
                                                               QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------------
 Insert on uuid7_keys  (cost=0.00..22500.00 rows=0 width=0) (actual time=2030.731..2030.731 rows=0 loops=1)
   ->  Function Scan on generate_series  (cost=0.00..12500.00 rows=1000000 width=16) (actual time=46.894..1479.223 rows=1000000 loops=1)
 Planning Time: 0.030 ms
 Execution Time: 2032.296 ms
(4 rows)

ulid=# EXPLAIN ANALYSE INSERT INTO ulid_keys(id) SELECT gen_ulid() FROM generate_series(1, 1000000);
                                                               QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------------
 Insert on ulid_keys  (cost=0.00..22500.00 rows=0 width=0) (actual time=1665.380..1665.380 rows=0 loops=1)
   ->  Function Scan on generate_series  (cost=0.00..12500.00 rows=1000000 width=32) (actual time=46.719..1140.979 rows=1000000 loops=1)
 Planning Time: 0.029 ms
 Execution Time: 1666.867 ms
(4 rows)

Monotonicity

This extension supports monotonicity through gen_monotonic_ulid() function. To achive this, it uses PostgreSQL's shared memory and LWLock to store last generated ULID.

To be able to use monotonic ULID's, it is necessary to add this extension to postgresql.conf's shared_preload_libraries configuration setting.

shared_preload_libraries = 'ulid'	# (change requires restart)

ulid=# EXPLAIN ANALYSE SELECT gen_ulid() FROM generate_series(1, 1000000);
                                                            QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------
 Function Scan on generate_series  (cost=0.00..12500.00 rows=1000000 width=32) (actual time=47.207..2908.978 rows=1000000 loops=1)
 Planning Time: 0.035 ms
 Execution Time: 4053.482 ms
(3 rows)

ulid=# EXPLAIN ANALYSE SELECT gen_monotonic_ulid() FROM generate_series(1, 1000000);
                                                            QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------
 Function Scan on generate_series  (cost=0.00..12500.00 rows=1000000 width=32) (actual time=46.479..2586.654 rows=1000000 loops=1)
 Planning Time: 0.037 ms
 Execution Time: 3693.901 ms
(3 rows)

ulid=# EXPLAIN ANALYZE INSERT INTO users (name) SELECT 'Client 1' FROM generate_series(1, 1000000);
                                                               QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------------
 Insert on users  (cost=0.00..12500.00 rows=0 width=0) (actual time=8418.257..8418.261 rows=0 loops=1)
   ->  Function Scan on generate_series  (cost=0.00..12500.00 rows=1000000 width=64) (actual time=99.804..3013.333 rows=1000000 loops=1)
 Planning Time: 0.066 ms
 Execution Time: 8419.571 ms
(4 rows)

ulid=# EXPLAIN ANALYZE INSERT INTO users (name) SELECT 'Client 2' FROM generate_series(1, 1000000);
                                                               QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------------
 Insert on users  (cost=0.00..12500.00 rows=0 width=0) (actual time=8359.558..8359.561 rows=0 loops=1)
   ->  Function Scan on generate_series  (cost=0.00..12500.00 rows=1000000 width=64) (actual time=64.449..2976.754 rows=1000000 loops=1)
 Planning Time: 0.090 ms
 Execution Time: 8360.840 ms
(4 rows)

Pros

1. Monotonic ULIDs are better for indexing, as they are sorted by default.
2. Monotonic ULIDs slightly faster than gen_ulid() when generating lots of ULIDs within one millisecond. Because, in this case, there is no need to generate random component of ULID. Instead it is just incremented.

Cons

1. Previously generated ULID is saved in shmem and accessed via LWLock. i.e. it is exclusive for function invocation within database. Theoretically this can lead to slowdowns.

   ...But, in practice (at least in our testing) gen_monotonic_ulid() is slightly faster than gen_ulid().

2. Extensions that use shared memory must be loaded via postgresql.conf's shared_preload_libraries configuration setting.

   ...But, it only affects gen_monotonic_ulid() function. Other functions of this extension will work normally even without this config.

3. Monotonic ULIDs may overflow and throw an error.

   ...But, chances are negligible.

Usage

Use the extension in the database:

CREATE EXTENSION ulid;

Create a table with ulid as a primary key:

CREATE TABLE users (
  id ulid NOT NULL DEFAULT gen_ulid() PRIMARY KEY,
  name text NOT NULL
);

Or, create a table with monotonic ulid as a primary key:

CREATE TABLE users (
  id ulid NOT NULL DEFAULT gen_monotonic_ulid() PRIMARY KEY,
  name text NOT NULL
);

Operate it normally with text in queries:

SELECT * FROM users WHERE id = '01ARZ3NDEKTSV4RRFFQ69G5FAV';

Cast ulid to timestamp:

ALTER TABLE users
ADD COLUMN created_at timestamp GENERATED ALWAYS AS (id::timestamp) STORED;

Cast timestamp to ulid, this generates a zeroed ULID with the timestamp prefixed (TTTTTTTTTT0000000000000000):

-- gets all users where the ID was created on 2023-09-15, without using another column and taking advantage of the index
SELECT * FROM users WHERE id BETWEEN '2023-09-15'::timestamp::ulid AND '2023-09-16'::timestamp::ulid;

Installation

Use pgrx. You can clone this repo and install this extension locally by following this guide.

You can also download relevant files from releases page.

Troubleshooting

If you encounter the exclusive lock error while using pgx_ulid, follow these steps to resolve the issue:

1. Alter the system to set shared_preload_libraries to ulid by running the following SQL command:

   ALTER SYSTEM SET shared_preload_libraries = 'ulid';

2. Restart the PostgreSQL service to apply the changes. The command to restart PostgreSQL depends on your system.

3. Verify that ulid is successfully loaded into shared libraries by executing:

   SHOW shared_preload_libraries;

Contributors

Here is a list of Contributors

TODO

License

MIT/X11

Bug Reports

Report here.

Creator

Pavan Kumar Sunkara (pavan.sss1991@gmail.com)

Follow me on github, twitter

Footnotes

1. You can convert the ulid into uuid or bytea and store it like that. ↩ ↩² ↩³

2. Supports casting indirectly through bytea. ↩