The perils of UUID primary keys in SQLite

6/6/2026 at 12:43:29 AM

UUIDs are way over used. There is almost always a better key to use, usually a bigint for databases. If you're making some kind of leaderless distributed data store, then maybe, but even then there are other ID sharding strategies I'd go for first depending on the constraints.

For a single database, bigints are smaller and faster, with less footguns.

UUIDs can be nice for an opaque public ID, however I'd still prefer something like a Sqid for space and usability.

by blopker

6/6/2026 at 5:31:18 PM

Providing an ID from the client is a big advantage that's missing though. Especially if you want a UI with optimistic rendering that's dealing with something async

by Fire-Dragon-DoL

6/6/2026 at 2:39:35 AM

> bigints are smaller and faster, with less footguns

But be careful!! Javascript WILL interpret your bigints as Number() and round them down because they are too big without telling you!!!

Famously seen by every snowflake user that has interacted with Javascript, quite an annoying problem.

by Fabricio20

6/6/2026 at 7:32:13 AM

Good trick is to prefix all such keys with magic, i.e. a couple of letters that identify type type of key.

Then it will always be a string and you will be free to change the format/type of the key in the future to UUID or whatever you like.

by silvestrov

6/6/2026 at 3:43:07 PM

Rule of thumb: if you’re not doing math with a value, it’s not a number.

by zmj

6/6/2026 at 10:29:30 AM

Using a Feistel cipher and base 32 encoding at the boundaries of the system can help catching vibe coded edge code that attempt to decode identifiers in javascript. It also somewhat obfuscate the cardinalities and fill rate of the tables.

by Piezoid

6/6/2026 at 10:03:49 AM

This can be avoided by supplying a reviver:

    const json = '{ "a": 9007199254740993 }'
    JSON.parse(json, (_key, value, context) => /^\d+$/.test(context.source) ? BigInt(context.source) : value)

by sheept

6/6/2026 at 2:52:21 AM

Fortunately we're seeing more JS DB libraries offering to read large numbers as the BigInt type.

by spiffytech

6/6/2026 at 5:53:27 AM

But frustratingly, a JS BigInt is nothing like a BigInt in any other language.

In JS - BigInt is 64bit integer.

In anything else - BigInt is a arbitrarily large integer.

by shakna

6/6/2026 at 6:02:20 AM

Hm? JavaScript BigInts are arbitrary precision, and you need to use methods like BigInt.asIntN(64, a) to convert them to 64 bits

by anematode

6/6/2026 at 7:27:57 AM

I hate this so much because you can’t nicely serialise a BigInt as JSON. Using a string is nicer but it only makes sense where int64 is used as an ID, not where it’s used as a number; and you don’t wanna have to configure this per field per query.

by mort96

6/6/2026 at 10:06:18 AM

You can serialize a BigInt by specifying a replacer:

    const obj = { a: 9007199254740993n }
    JSON.stringify(obj, (_key, value) => typeof value === 'bigint' ? JSON.rawJSON(value.toString()) : value)

by sheept

6/6/2026 at 10:27:23 AM

And then you end up with strings on the other side, not numbers.

by mort96

6/6/2026 at 10:46:42 AM

No you don't? The example I gave produces

    {"a":9007199254740993}

not

    {"a":"9007199254740993"}

by sheept

6/6/2026 at 2:20:07 PM

Oh, that's much worse! The JSON string `{"a":9007199254740993}` decodes to the object `{"a":9007199254740992}` with typical JSON parsers like JavaScript's `JSON.parse`.

by mort96

6/6/2026 at 8:11:26 AM

JSON has arbitrary length numbers in the spec only.

by nh2

6/6/2026 at 10:26:36 AM

Completely and utterly irrelevant.

by mort96

6/6/2026 at 6:50:36 AM

This is simply not true? Or maybe I misunderstand what you mean?

by Etheryte

6/6/2026 at 3:10:03 AM

!!

Node.js drivers will correctly read int64 as string or bigint, not number.

E.g. pg for PostgreSQL

Maybe there’s a buggy driver but I don’t know it.

by paulddraper

6/6/2026 at 5:36:39 PM

Browser!! The browser reads it as Number. If your rest api returns {"id": 1324535222364012585} for example, javascript will try and parse that as number from the response!!!

You can of course, change the api such that it does {"id": "1324535222364012585"} instead and voila, it will no longer try parsing it as number. Or the many other workarounds people have recommended above (like appending a prefix, or using a different encoding), but why is it trying to parse a number thats too big and instead of throwing it just rounds down without telling you????!

by Fabricio20

6/6/2026 at 2:16:11 AM

UUIDs also have a nice benefit of it being impossible to query the wrong table with one if you mixup what an FK goes to

by JamesSwift

6/6/2026 at 2:49:26 AM

Yeah this is nice - also helps with grepping dump files.

by pyuser583

6/6/2026 at 4:30:02 AM

How is this done?

by mamcx

6/6/2026 at 4:49:22 AM

They just mean you catch incorrect joins more easily because there is usually no overlap in keys between unrelated tables. Using int, you’re usually going to have some shared values between two unrelated tables.

by nickpeterson

6/6/2026 at 4:47:11 AM

Statistically impossible to inadvertently generate a collision using UUID keys. UUID is designed to be unique when generated across any computer system. Practically speaking if you have an exactly matching pair of UUIDs from disparate system you have found the exact record match. The name gives a hint "Universally unique identifier". -Not a cryptographer.

by sudoshred

6/6/2026 at 9:10:24 AM

It definitely is possible, just very improbable

by usrnm

6/6/2026 at 9:35:44 AM

That’s probably what’s meant by statistically impossible.

by echoangle

6/6/2026 at 4:53:42 AM

The U means if you join the wrong table your join will always come up empty.

It does not actually make it impossible to query the wrong table it just tells you quickly when you’ve done so.

by masklinn

6/6/2026 at 9:54:43 AM

You can achieve this with numeric sequences too, by having a consistent step and unique offset in all your sequences. For example, if you will never exceed 16 types, reserve four bits as the type discriminant. (You don’t have to use powers of two, but it may be convenient.)

All sequences use step 16.

Type A has discriminant/offset 0, yielding IDs {0, 16, 32, 48, 64, …}.

Type B has discriminant/offset 1, mapping to IDs {1, 17, 33, 49, 65, …}.

All the way up to Type P with discriminant/offset 15 and IDs {15, 31, 47, 63, 79, …}.

This is also trivially invertible so that you can determine the type from the ID.

A more common approach is to make IDs opaque strings and put a type prefix—A0, B12, P34, that kind of thing. But this way you can keep it as a number, if you wish.

by chrismorgan

6/6/2026 at 3:52:24 PM

What are uuid foot guns?

by PUSH_AX

6/6/2026 at 6:51:05 AM

Yes this matters even more if you are doing a lot of joins. Naive string UUIDs are 32 bytes (though I use binary uuid in the post which is 16) compared to 8 bytes for a 64-bit int. This matters even more with sqlite as it uses varint encoding. The upshot of all this is your indexes take up a lot less space in memory.

by andersmurphy

6/6/2026 at 1:18:51 AM

I am finding UUIDs help a lot if your primary schema consumer is an LLM.

Inappropriate aliasing of integer keys allows for silent errors in queries because it will actually return some result a lot of the time. A UUID is immune to this problem. The model recognizes its mistake a lot more reliably when previously non-empty tables start showing up empty after attempting a join.

by bob1029

6/6/2026 at 2:36:41 AM

No one ever got fired for using UUIDs

by crubier

6/6/2026 at 11:29:41 AM

Thanks for the benching, Anders! So grateful for the stuff you've shared over the years. Invariably, every single post has been useful and/or educational to me.

I read this post more as an illustration of the *value* of UUIDv7 as primary key, over integer primary keys, in lieu of minimal loss of read/write performance, and marginally more data on disk bloat.

SQLite's automatic integer rowID primary key is a no-brainer, when the SQLite application is local-only, such as application storage format (mobile and desktop). Or is never intended to grow beyond a single server instance. Basically, where each SQLite file is private to a singular instance of the application.

However, if there is even an outside chance of needing to cooperate across application instances, e.g. the minimal limit case of a personal knowledge base that should seamlessly sync across a person's devices, as well as a hosted service, then a high-quality sequential random ID starts to make a lot more sense. (No-brainer arbitrary table merges / splits / remerges, de-duplication, etc.)

Random ID primary key is a bad idea period, whether it be the UU kind or the SQ kind, or any other kind. As far as my DB knowledge goes, this class of ID destroys all tree-algorithms, and we are stuck with the fact that there is no practically better way, than an appropriate tree-structure, to group and organise a meaningful amount of data, efficiently and effectively.

by adityaathalye

6/6/2026 at 5:00:15 PM

I've updated the article with the correct rowid alias (integer not int) so the rowid version is now 715ms. I've also added an example of rowid and a secondary index UUID4, and that also seems to be bad for performance (as although it's not a clustered index it's still random inserts into a b-tree).

by andersmurphy

6/6/2026 at 11:32:22 AM

Aside: Specific to SQLite...

Thanks to its oh so convenient automatic integer rowIDs, I believe one can amortise some of the other overheads of UUIDv7s for "in-between" queries, viz. indices, joins, ctes, virtual tables etc., with appropriate schema / query design.

by adityaathalye

6/6/2026 at 8:27:55 AM

So UUID isn't the problem but UUID v4 is, just like any random ID-scheme, correct?

UUID v7 so far seems like the best solution if you want UUID benefits and ordering.

by jdthedisciple

6/6/2026 at 2:09:19 PM

It's " WITHOUT ROWID" problem.

Why would you force database to order rows on the drive according to random id?

by scotty79

6/6/2026 at 5:20:24 PM

If you had read the article, you'd have seen that UUIDv4 with Rowid was slightly slower than UUIDv7

by chromatin

6/6/2026 at 8:37:16 AM

My rule for primary keys and id's is simple: Sequential integer (or bigint) as the PK and if I need to make it public, I have a GUID (or UUID) in the row too, e.g. tbl_person would have Id (int|bigint) and person_guid as (UUID).

The Integer id is used for joins and looks ups and such but that's it. If I need to send anything to the frontend or outside of the app/DB then that's the UUID.

by ItsBob

6/6/2026 at 6:35:04 AM

This is actually a draft. I Wanted to add more details about how this changes with row size etc. I might get time to update it later today.

by andersmurphy

6/6/2026 at 11:33:00 AM

Maybe you could explain why one would use "without rowid" in the first place.

I get saving 8 bytes per row seems attractive, but the tradeoff is not explained.

by ysleepy

6/6/2026 at 3:25:28 PM

Update the article there's now a section for UUID4 with rowid. It's less bad than UUID4 without rowid but it's still about 4-6x slower than UUID7 without rowid.

by andersmurphy

6/6/2026 at 3:28:43 PM

[flagged]

by keynha

6/6/2026 at 7:49:39 AM

Why would you use UUIDs a primary keys? Let SQLite use rowids internally (which is automatic and invisible), and have a different (indexed) column with UUID if you need that for publishing the ID somewhere.

by bambax

6/6/2026 at 10:09:25 AM

UUID as key is useful when you have a distributed system where multiple workers create items independently

by elcomet

6/6/2026 at 2:46:54 PM

Because another app can then create the id and add it to the db later.

by victorbjorklund

6/6/2026 at 2:48:24 AM

Oh gosh the ints v uuids debate for pks. This is worse than vim v eMacs or brackets v braces.

by pyuser583

6/6/2026 at 7:42:04 AM

I enjoy these carefully worded posts from Anders Murphy, illustrative and informative, not opinionated and preachy. Very useful, it’s great to see the process, and ofc bookmarkeable material for sharing with others.

by ac50hz

6/6/2026 at 1:44:47 AM

Isn't the solution just to use the rowid (after doing the read-id-after-insert dance)?

How much trouble does SQLite reysing rowid's actually cause?

by w10-1

6/6/2026 at 6:37:47 AM

You don't even need to that. SQLite auto increments the ids and is a single writer (which you should be coordinating at the application level.

Regular rowids are definitely the way to go if you can use them.

by andersmurphy

6/6/2026 at 10:53:24 AM

The script to create the benchmark numbers appears to be inserting 100 batches, not 10. (The benchmark numbers in the table appear to be consistent with the text, so I guess the actual script used to create them was correct.)

by kjgkjhfkjf

6/6/2026 at 2:54:45 PM

Yeah that was just a holdover from when I was playing with smaller batch sizes. It's not in the actual linked source.

by andersmurphy

6/5/2026 at 11:29:39 PM

Perils of “UUIDv4”. Everyone knows that’s what UUIDv7 was really for, and you should always convert that to binary to optimize everything.

by yepyoukno

6/6/2026 at 4:34:19 PM

Doesn't Postgres' UUID type just do this for you anyway?

Why would you store it as as str column and not the inbuilt type for this?

https://www.postgresql.org/docs/current/datatype-uuid.html

If you are using SQLite well I guess that doesn't work.

by antihero

6/6/2026 at 12:58:39 AM

Small nit: uuid7 is 128 bits (16 bytes) by definition. So there’s no need to convert it to binary. It already is. Unless you’re working with a stringified version of the uuid7.

by JSR_FDED

6/6/2026 at 1:03:30 AM

Oh yes, I meant don’t store as an ID in its string format!

by yepyoukno

6/6/2026 at 2:33:32 AM

It's just s dumb as storing dates as strings, but people still do it.

by dexterdog

6/6/2026 at 7:09:12 AM

But SQLite does not have a native datetime type so you have to use strings

by littlecranky67

6/6/2026 at 7:52:31 AM

You can use an integer

by voakbasda

6/6/2026 at 2:36:51 PM

How do I know the time zone of an integer? Sure there are plenty of cases where one doesn't care, but there are also many cases where the original time zone is important.

by Volundr

6/6/2026 at 5:40:11 PM

The integer is a UTC time so it can be sorted. If you need the time zone you store than in a smaller field.

by dexterdog

6/6/2026 at 2:47:13 PM

other comment said it already, timezone information is not saved. Easiest is just to use a string.

by littlecranky67

6/6/2026 at 6:48:55 AM

But also one of the recommended ways of doing it, as it has no native Datetime type.

by cenamus

6/6/2026 at 3:43:33 AM

> and you should always convert that to binary to optimize everything

I disagree. I tried this once. Now you need a client access layer to touch the DB in any context. All your console tools no longer work well or at all. If they show up in URLs you need to deoptimize them for transport.

You give up a lot of convenience for this optimization. You should be absolutely sure your design requires it before using it.

by themafia

6/6/2026 at 7:15:28 AM

Is this relevant for other databases? For postgres for example, which supports concurrent writers, wouldn't sequential keys lead to contention on the page at the frontier?

by cropcirclbureau

6/6/2026 at 8:00:49 AM

That's a good question. I don't know the answer. I will say, generally you can get higher write throughput with a single writer. Even more so if you're prepared to shard along boundaries where you don't need atomic transactions.

Contention and coordination are real killers, concurrent writes (that require coordination like postgres) often underdeliver.

by andersmurphy

6/5/2026 at 11:38:38 PM

Wait how is sqlite doing a million inserts a second?

by dumbledorf

6/6/2026 at 12:52:13 AM

In batches

by JSR_FDED

6/6/2026 at 12:33:55 AM

sqlite is really fast. I'm surprised it's only a million.

by kg

6/6/2026 at 6:44:54 AM

It's running on an M1 mac with synchronous full. Wouldn't surprise me if it's possible to get higher numbers.

by andersmurphy

6/6/2026 at 12:46:06 AM

':memory:'

https://sqlite.org/inmemorydb.html

by smitty1e

6/6/2026 at 4:49:29 AM

Except this source code is not using :memory: The linked source code has

    (defonce db
      (d/init-db! "db/db.db"
        {:pool-size 4 :pragma {:synchronous "FULL"}}))

That's writing to disk.

by KPGv2

6/6/2026 at 6:43:22 AM

Yes it's writing to disk (on a M1 mac which has terribly slow fsync). But, because of the transaction the fsync dance is done once per batch. Each row is the id + a 50 byte data blob.

There's only one index so there's no real write amplification. The numbers will go down as you add more data and indexes.

by andersmurphy

6/6/2026 at 11:58:53 AM

How much time is `(random-uuid7-bytes)` taking?

by michaelcampbell

6/6/2026 at 5:44:33 PM

[flagged]

by knightops_dev

6/6/2026 at 5:52:59 AM

If you need (or want the convenience of) a uuid and the time of creation is not secret then use ulids eg uuid v7.

by wood_spirit