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## Problem These changes are part of building seamless tenant migration, as described in the RFC: - https://github.com/neondatabase/neon/pull/5029 ## Summary of changes - A new configuration type `LocationConf` supersedes `TenantConfOpt` for storing a tenant's configuration in the pageserver repo dir. It contains `TenantConfOpt`, as well as a new `mode` attribute that describes what kind of location this is (secondary, attached, attachment mode etc). It is written to a file called `config-v1` instead of `config` -- this prepares us for neatly making any other profound changes to the format of the file in future. Forward compat for existing pageserver code is achieved by writing out both old and new style files. Backward compat is achieved by checking for the old-style file if the new one isn't found. - The `TenantMap` type changes, to hold `TenantSlot` instead of just `Tenant`. The `Tenant` type continues to be used for attached tenants only. Tenants in other states (such as secondaries) are represented by a different variant of `TenantSlot`. - Where `Tenant` & `Timeline` used to hold an Arc<Mutex<TenantConfOpt>>, they now hold a reference to a AttachedTenantConf, which includes the extra information from LocationConf. This enables them to know the current attachment mode. - The attachment mode is used as an advisory input to decide whether to do compaction and GC (AttachedStale is meant to avoid doing uploads, AttachedMulti is meant to avoid doing deletions). - A new HTTP API is added at `PUT /tenants/<tenant_id>/location_config` to drive new location configuration. This provides a superset of the functionality of attach/detach/load/ignore: - Attaching a tenant is just configuring it in an attached state - Detaching a tenant is configuring it to a detached state - Loading a tenant is just the same as attaching it - Ignoring a tenant is the same as configuring it into Secondary with warm=false (i.e. retain the files on disk but do nothing else). Caveats: - AttachedMulti tenants don't do compaction in this PR, but they do in the follow on #5397 - Concurrent updates to the `location_config` API are not handled elegantly in this PR, a better mechanism is added in the follow on https://github.com/neondatabase/neon/pull/5367 - Secondary mode is just a placeholder in this PR: the code to upload heatmaps and do downloads on secondary locations will be added in a later PR (but that shouldn't change any external interfaces) Closes: https://github.com/neondatabase/neon/issues/5379 --------- Co-authored-by: Christian Schwarz <christian@neon.tech>