You can guess the time the system took between 2 uuid v7 id's.
They can only be used if they're not shown to the user. (so not in the form mysite.com/mypage? id=0190854d-7f9f-78fc-b9bc-598867ebf39a)
A big serial starting at a high number can't provide the time information.
If you use only uuid in your outwards facing api then you still have the problem of slow queries. Since you need them to find the object (as mentioned below)
UUIDv7 has a random part, can be created distributedly, and indexes well.
It’s the best choice for modern application that support distributed data creation.
For me the bigger thing is the randomness. A uid being random for a given row means the opposite is true; any given index entry points to a completely random heap entry.
When backfilling this leads to massive write amplification. Consider a table with rows taking up 40 bytes, so roughly 200 entries per page. If I backfill 1k rows sorted by the id then under normal circumstances I'd expect to update 6-7 pages which is ~50kiB of heap writes.
Whereas if I do that sort of backfill with a uid then I'd expect to encounter each page on a separate row. That means 1k rows backfilled is going to be around 8MB of writes to the heap.
We do use a custom uuid generator that uses the timestamp as a prefix that rotates on a medium term scale. That ensures we get some degree of clustering for records based on insertion time, but you can't go backwards to figure out the actual time. It's still a problem when backfilling and is more about helping with live reads.
This is problematic if you try to depend on the ordering. Nothing is stopping some batch process that started an hour ago from committing a value 100k lower than where you thought the sequence was at. That's an extreme example but the consideration is the same when dealing with millisecond timeframes.
Also, the external thing isn't just for exposing it out to your own apps via APIs, but way more importantly for providing an unmistakable ID to store within external related systems. For example, in your Stripe metadata.
Doing this ensures that ID either exists in your own database or does not, regardless of database rollbacks, database inconsistencies etc. In those situations a numeric ID is a big question mark: Does this record correspond with the external system or was there a reuse of that ID?
I've been burnt taking over poorly managed systems that saved numeric IDs externally, and in trying to heal and migrate that data, ran into tons of problems because of ill-considered rollbacks of the database. At least after I leave the systems I build won't be subtly broken by such bad practices in the future.
Ordering over an insertion timestamp is not enough if two records may have the same timestamp: You may miss a record (or visit a record twice) across multiple queries.
The UUID sorting works in the common case, but if you happen to end your batch near the current time, you still run the risk of losing a few records if the insert frequency is sufficiently high. Admittedly this is only a problem when you are batching through all the way to current insertions.
Also, security can be built around not allowing querying records which are not yours.
I'm all for a little security through obscurity including UUIDs but it shouldn't be the sole thing. Easier to generate a UUID for the sequential and let the database do what it does best (relate many serials among each other).
The other part is being able to use what's built into the database out of the box without a lot more configuration.
Selfishly, I always appreciate learning more about Postgres though :)
The way I see it is that uuid v7 in itself is great for some use but not for all uses.
You always have to remember that a v7 always carries the id's creation time as metadata with it, whether you want it or not. And if you let external users get the v7, they can get that metadata.
I'm not a security expert but I know enough to know that you should only give the minimal data to a user.
My only guess is that v7 being so new, attacks aren't widespread for now, and I know why the author decided not to focus on "if UUID is the right format for a key", because the answer is no 99% of the time.
The use of UUIDs for documents may come from a no-sql background.
I use bigserials for relational data in relational databases, and if there is a unique document value needed, a UUID is good.
You would be immediately leaking how many orders a day your business is getting with sequential id.
Which is fine for almost all of them. All brick and mortar stores "leak" this too; it's really not that hard to guess number of orders for most businesses, and it's not really a problem for the overwhelming majority.
And "Hi, this is Martin, I'd like to ask a question about order 2bf8aa01-6f4e-42ae-8635-9648f70a9a05" doesn't really work. Neither does "John, did you already pay order 2bf8aa01-6f4e-42ae-8635-9648f70a9a05" or "Alice, isn't 2bf8aa01-6f4e-42ae-8635-9648f70a9a05 the same as what we ordered with 7bb027c3-83ea-481a-bb1e-861be18d21ea?"
Especially for order IDs UUIDs are huge PITA because unlike user IDs and other more "internal" IDs, people can and do want to talk about them. You will need some secondary human-friendly unique ID regardless (possibly obfuscated, if you really want to), and if you have that, then why bother giving UUIDs to people?
For extra spice, in some places this is legislated as a per-seller sequence, and in others as a per-customer sequence, so there’s no policy you can apply globally, and this once again highlights the separation of concerns between a primary key and a record locator/identifier.
Same in France. I thought it was a pretty common requirement.
That’s surprising. In Denmark gaps are not allowed. You have to account for all invoices and if you have an invoice numbered 50, then you have at least 50 invoices to account for.
However you are allowed to have multiple sequences, differentiated through a prefix, but all starting at 0. That’s what we recently did to switch invoice generation tools (we actually still run both of them alongside each other atm).
Of course you could still drop some invoices from the end when you do this, but I guess tax authorities accept that risk.
1. The UUIDs should be ordered internally, for B-tree performance
2. The UUIDs should not be ordered externally, for security reasons
Why not use encryption? The unencrypted ID is a sequential id, but as soon as it leaves the database, it's always encrypted. Like, when getting it out:
SELECT encrypt(id) FROM table WHERE something = whatever;
UPDATE table SET something = whatever WHERE id = decrypt(<encrypted-key>)
My take is it's rarely necessary to have a token, that you give to an external entity, that has any embedded metadata all - 99.9% of apps aren't operating at a scale where even a million-key hashmap sitting in ram and syncing changes to disk on update would cause any performance difference.
It seems to me: the actual value of knowing these ids/timestamps to a hacker is tiny, but it's not nothing (German tank problem and all that). Like, if a hacker was able to decode the timestamps, it's not ideal, but it's not like a catastrophe either (especially given that half the people in this thread thinks it has no security value at all). Given that threat model, a simple scheme like I suggested seems fine to me.
But it is.
If you have a password in a system, you want to rotate it regularly or at least have that ability (for example, when angry colleague leaves).
Because then you have a key management problem, which adds complexity.
Are you then not doing security by randomness if that is the thing that worries you?