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NB: effectively a no-op in the neon env since the handling is config gated in storcon ## Problem When a pageserver suffers from a local disk/node failure and restarts, the storage controller will receive a re-attach call and return all the tenants the pageserver is suppose to attach, but the pageserver will not act on any tenants that it doesn't know about locally. As a result, the pageserver will not rehydrate any tenants from remote storage if it restarted following a local disk loss, while the storage controller still thinks that the pageserver have all the tenants attached. This leaves the system in a bad state, and the symptom is that PG's pageserver connections will fail with "tenant not found" errors. ## Summary of changes Made a slight change to the storage controller's `re_attach` API: * The pageserver will set an additional bit `empty_local_disk` in the reattach request, indicating whether it has started with an empty disk or does not know about any tenants. * Upon receiving the reattach request, if this `empty_local_disk` bit is set, the storage controller will go ahead and clear all observed locations referencing the pageserver. The reconciler will then discover the discrepancy between the intended state and observed state of the tenant and take care of the situation. To facilitate rollouts this extra behavior in the `re_attach` API is guarded by the `handle_ps_local_disk_loss` command line flag of the storage controller. --------- Co-authored-by: William Huang <william.huang@databricks.com>