Must have:

• report consumption from tenants
• implement configuration API
• implement throttling
• don't charge for failed KV operations
• mechanism for reasonable behavior when tenant_usage table is not available
• reduce TTL for system.tenant_usage
• idempotent consumption updates
• adjust server-side tenant rate limiting
• back up tenant usage metadata
• pgwire bytes usage
• finalize cost model settings

Should have:

• implement shares to divide the throttled rate among multiple instances.
• use counters instead of gauges for metrics (tenantcostserver: use counters instead of gauges for tenant usage metrics #68291)
• make sure tenant-side cluster settings don't allow tenants to avoid charges
• revisit the way metrics are published; see discussion

Running list of PRs that still need to be backported (to release-21.2 AND the staging-serverless branch):

• release-21.2: multitenant: implement fallback rate and pass next live instance ID #70727
• release-21.2: backup: include tenant usage data in backup #70829
• release-21.2: kv: deflake TestTenantRateLimiter #70737
• release-21.2: tenantcostclient: deflake TestDataDriven #70844
• release-21.2: sql: change system.tenant_usage to use a single consumption column #70906
• release-21.2: multitenant: add pgwire bytes component to tenant cost #70954
• release-21.2: multitenant: exempt sqlliveness operations from cost control #71123
• release-21.2: multitenant: only charge for pgwire egress and update cost model settings #71286
• release-21.2: tenantcostclient: smooth over debt payback #71287

Jira issue: CRDB-9052