John Spray ecb01834d6 pageserver: implement utilization score (#8703) ...

## Problem

When the utilization API was added, it was just a stub with disk space
information.

Disk space information isn't a very good metric for assigning tenants to
pageservers, because pageservers making full use of their disks would
always just have 85% utilization, irrespective of how much pressure they
had for disk space.

## Summary of changes

- Use the new layer visibiilty metric to calculate a "wanted size" per
tenant, and sum these to get a total local disk space wanted per
pageserver. This acts as the primary signal for utilization.
- Also use the shard count to calculate a utilization score, and take
the max of this and the disk-driven utilization. The shard count limit
is currently set as a constant 20,000, which matches contemporary
operational practices when loading pageservers.

The shard count limit means that for tiny/empty tenants, on a machine
with 3.84TB disk, each tiny tenant influences the utilization score as
if it had size 160MB.

2024-08-13 15:15:55 +01:00

..

src

pageserver: implement utilization score (#8703)

2024-08-13 15:15:55 +01:00

Cargo.toml

feat: bare-bones /v1/utilization (#6831)

2024-02-22 13:58:59 +02:00