[inoop]

I'd be curious as well to see a more complete cost-benefit analysis, and I'd be especially interested in labor cost.

We don't know how much time and head count Uber committed to this project, but I would be impressed if they were able to pull this off with fewer than 6-8 people. We can use that to get a very rough lower-bound cost estimate.

For example, AWS internally uses a rule of thumb where each developer should generate about $1MM ARR (annual recurring revenue). So, if you have 20 head count, your service should bring in about $20MM annually. If Uber pulled this off with a team of ~6 engineers, by AWS logic, they should about break even.

Another rule of thumb I sometimes see applied is 2x developer salary. So for example, let's assume a 7-person team of 2xSDE1, 3xSDE2, 1xSDE3, and 1xSTAFF, then according to levels.fyi that would be a total annual salary of $2.3MM. Double that, and you get $4.6MM/year to justify that team annual cost footprint, which is still less than $6MM.

Of course, this is assuming a small increase in headcount to operate this new, custom data store, and does not factor in a potentially significant development and migration cost.

So unless my math is completely off, it sounds to me like the cost of development, migration, and ownership is not that far off from the cost of the status quo (i.e. DynamoDb).

[shrubble]

If the savings are 6 million per year, then in later years it should pay off since the development is a one time cost.

[inoop]

The cost doesn't suddenly drop to zero once development is done. Typically a system of this complexity and scale requires constant maintenance. You'll need someone to be on-call (pager duty) to respond to alarms, you'll need to fix bugs, improve efficiency, apply security patches, tune alarms and metrics, etc.

In my experience you probably need a small team (6-8 people) to maintain something like this. Maybe you can consolidate some things (e.g. if your system has low on-call pressure, you may be able to merge rotations with other teams, etc.) but it doesn't go down to zero.

[shrubble]

If you follow the various links on the Uber site, you see that they have multiple applications sitting on the same database. see https://www.uber.com/blog/schemaless-sql-database/ . It's not just 1 design of a database, with 1 application on top...

[Rastonbury]

Not an engineer, but something like this takes 6-8 people working on only this for a full year?

[inoop]

That has been my experience, yes. You need one full-time manager, one full-time on-call/pager duty (usually a rotation), and then 4-6 people doing feature development, bug fixes, and operational stuff (e.g. applying security patches, tuning alarms, upgrading instance types, tuning auto-scaling groups, etc. etc.).

Maybe you can do it a bit cheaper, e.g. with 4-6 people, but my point is that there's an on-going cost of ownership that any custom-built solution tends to incur.

Amortizing that cost over many customers is essentially the entire business model of AWS :)