[wincent]

Linked in the article is this other one, "Partitioning GitHub’s relational databases to handle scale" (https://github.blog/2021-09-27-partitioning-githubs-relation...). That describes how there isn't just one "main primary" node; there are multiple clusters, of which `mysql1` is just one (the original one — since then, many others have been partitioned off).

[throwusawayus]

from that article it sounds like they are mostly doing "functional partitioning" (moving tables off to other db primary/replica clusters) rather than true sharding (splitting up tables by ranges of data)

functional partitioning is a band-aid. you do it when your main cluster is exploding but you need to buy time. it ultimately is a very bad thing, because generally your whole site is depenedent on every single functional partition being up. it moves you from 1 single point of failure to N single points of failure!

[dikei]

>> functional partitioning is a band-aid.

I disagree, functional partitioning is not a band-aid, but an architectural changes that in the end can reap much more benefit than simple data sharding.

>> your whole site is dependent on every single functional partition being up. it moves you from 1 single point of failure to N single points of failure!

Not necessarily, it can also be that only some parts of your site are dead while others work perfectly fine.

[throwusawayus]

too idealistic. invariably some team (or usually many teams) don't properly gate some critical-path logic, they depend on some functional partition always being online and then boom much larger blast radius than intended

then they fix it in post-mortem but pattern just repeats. i have seen it so many times! used to be much worse in the earlier days of the cloud when VMs would go poof more often

[wincent]

Towards the end:

> In addition to vertical partitioning to move database tables, we also use horizontal partitioning (aka sharding). This allows us to split database tables across multiple clusters, enabling more sustainable growth.

[throwusawayus]

yes i know, the fact that this is a small blurb at the bottom of the article (which is largely about functional partitioning) exactly proves my point