How much does overwriting cost?

[janderland (Jon Anderson)]

I haven’t completely investigated, but I should be able to cache the categories and only perform reads if the metadataVersion key changes, therefore preventing the hot-read-key problem.

A new tool for managing layer metadata

I am moving discussion from https://github.com/apple/foundationdb/pull/1213 over to the forums. A common pattern in layers is that there is a rarely changing schema that needs to be validated within each transaction. These reads of a small amount of data can be a burden on clusters, because the reads are concentrated on a very small section of key space. The PR adds a key to the system keyspace which has its value sent to the client with every read version. This means that clients can see the …