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With Firestore, you're writing to many boxes. Because of that, you'll want to be on hot pages. With MySQL, you're writing to a single box.
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Is it that they truly want it distributed across the key space or distributed across the shards? Sequential UUIDs are a compromise - giving away a small amount of collision protection in order to gain what could be a significant efficiency boost in some circumstances (DB indexes being the main one). UUIDs, including those that increment from the start point, are intended not to collide with those generated elsewhere. > If you need something sequential then just use a much more simple number* You don't want to use sequential UUIDs in place of v4 UUIDs where security matters, or course, as it is easy to work the next in sequence. These are "atoms in several galaxies" level numbers. For most systems the chance of collision with sequential UUIDs is, while larger than with other types, still so small as to be inconsequential. Even if your system is up long enough to use 2^58 (2.88 10^17 if you want that in decimal) IDs generated this way, you still effectively have 64-bits of randomness even if the variant bits are present. Assuming the variant indicators are present, there is are 122 random bits. MS SQL Server's NEWSEQUENTIALID function returns something akin to a v4 UUID (fully random, aside from variant indicator bits, I'm not sure if the variant bits are respected in NEWSEQUENTIALIDs output or if it just returns a 128-bit number) but after the first is generated the rest follow in sequence until the sequence is reset (by a reboot). IIRC this is often a mix of hardware network address and a portion that is either random or based on a high-precision time, so it is still unlikely that you'll see collisions between machines. It depends on how the non-sequential part is derived.