alt Hacker NewsI do not understand why 128 bits is considered too big - you clearly can't have less, as on 64 bits the collision probability on real world workloads is just too high, for all but the smallest databases.
Auto-incrementing keys can work, but what happens when you run out of integers? Also, distributed dbs probably make this hard, and they can't generate a key on client.
There must be something in Postgres that wants to store the records in PK order, which while could be an okay default, I'm pretty sure you can this behavior, as this isn't great for write-heavy workloads.
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I doubt many real world use cases would run out of incrementing 64 bit ids - collisions if they were random sure, but i64 max is 9,223,372,036,854,775,807 - if each row took only 1 bit of space, that would be slightly more than an exabyte of data.
You won't run out of 64-bit integer. IMO, 64-bit integer (and even less for some tables that's not expected to grow much) it the best approach for internal database ID. If you want to expose ID, it might make sense to introduce second UUID for selected tables, if you want to hide internal ID.
The issue is more fundamental - if you have purely random keys, there's basically no spatial locality for the index data. Which means that for decent performance your entire index needs to be in memory, rather than just recent data. And it means that you have much bigger write amplification, since it's rare that the same index page is modified multiple times close-enough in time to avoid a second write.