Squashed commit of the following:

commit de90ba56d4
Author: Christian Schwarz <christian@neon.tech>
Date:   Mon Nov 27 14:47:26 2023 +0000

    expose generation number in API

commit ae2c7589f9
Author: Christian Schwarz <christian@neon.tech>
Date:   Mon Nov 27 14:53:13 2023 +0000

    pagectl: add subcommand to rewrite layer file history

libs/pageserver_api/src/models.rs

@@ -364,6 +364,8 @@ pub struct TenantInfo {
     /// If a layer is present in both local FS and S3, it counts only once.
     pub current_physical_size: Option<u64>, // physical size is only included in `tenant_status` endpoint
     pub attachment_status: TenantAttachmentStatus,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub generation: Option<u32>,
 }
 
 /// This represents the output of the "timeline_detail" and "timeline_list" API calls.
@@ -827,6 +829,7 @@ mod tests {
             state: TenantState::Active,
             current_physical_size: Some(42),
             attachment_status: TenantAttachmentStatus::Attached,
+            generation: None,
         };
         let expected_active = json!({
             "id": original_active.id.to_string(),
@@ -847,6 +850,7 @@ mod tests {
             },
             current_physical_size: Some(42),
             attachment_status: TenantAttachmentStatus::Attached,
+            generation: None,
         };
         let expected_broken = json!({
             "id": original_broken.id.to_string(),

pageserver/src/consumption_metrics.rs

@@ -269,7 +269,7 @@ async fn calculate_synthetic_size_worker(
             }
         };
 
-        for (tenant_id, tenant_state) in tenants {
+        for (tenant_id, tenant_state, _gen) in tenants {
             if tenant_state != TenantState::Active {
                 continue;
             }

pageserver/src/consumption_metrics/metrics.rs

@@ -197,7 +197,7 @@ pub(super) async fn collect_all_metrics(
         }
     };
 
-    let tenants = futures::stream::iter(tenants).filter_map(|(id, state)| async move {
+    let tenants = futures::stream::iter(tenants).filter_map(|(id, state, _)| async move {
         if state != TenantState::Active {
             None
         } else {

pageserver/src/disk_usage_eviction_task.rs

@@ -541,7 +541,7 @@ async fn collect_eviction_candidates(
 
     let mut candidates = Vec::new();
 
-    for (tenant_id, _state) in &tenants {
+    for (tenant_id, _state, _gen) in &tenants {
         if cancel.is_cancelled() {
             return Ok(EvictionCandidates::Cancelled);
         }

pageserver/src/http/routes.rs

@@ -790,11 +790,12 @@ async fn tenant_list_handler(
             ApiError::ResourceUnavailable("Tenant map is initializing or shutting down".into())
         })?
         .iter()
-        .map(|(id, state)| TenantInfo {
+        .map(|(id, state, gen)| TenantInfo {
             id: *id,
             state: state.clone(),
             current_physical_size: None,
             attachment_status: state.attachment_status(),
+            generation: (*gen).into(),
         })
         .collect::<Vec<TenantInfo>>();
 
@@ -823,6 +824,7 @@ async fn tenant_status(
             state: state.clone(),
             current_physical_size: Some(current_physical_size),
             attachment_status: state.attachment_status(),
+            generation: tenant.generation().into(),
         })
     }
     .instrument(info_span!("tenant_status_handler", %tenant_id))

pageserver/src/tenant.rs

@@ -1756,6 +1756,10 @@ impl Tenant {
         self.current_state() == TenantState::Active
     }
 
+    pub fn generation(&self) -> Generation {
+        self.generation
+    }
+
     /// Changes tenant status to active, unless shutdown was already requested.
     ///
     /// `background_jobs_can_start` is an optional barrier set to a value during pageserver startup

pageserver/src/tenant/mgr.rs

@@ -1542,7 +1542,8 @@ pub(crate) enum TenantMapListError {
 ///
 /// Get list of tenants, for the mgmt API
 ///
-pub(crate) async fn list_tenants() -> Result<Vec<(TenantId, TenantState)>, TenantMapListError> {
+pub(crate) async fn list_tenants(
+) -> Result<Vec<(TenantId, TenantState, Generation)>, TenantMapListError> {
     let tenants = TENANTS.read().unwrap();
     let m = match &*tenants {
         TenantsMap::Initializing => return Err(TenantMapListError::Initializing),
@@ -1550,12 +1551,12 @@ pub(crate) async fn list_tenants() -> Result<Vec<(TenantId, TenantState)>, Tenan
     };
     Ok(m.iter()
         .filter_map(|(id, tenant)| match tenant {
-            TenantSlot::Attached(tenant) => Some((id, tenant.current_state())),
+            TenantSlot::Attached(tenant) => Some((id, tenant.current_state(), tenant.generation())),
             TenantSlot::Secondary => None,
             TenantSlot::InProgress(_) => None,
         })
         // TODO(sharding): make callers of this function shard-aware
-        .map(|(k, v)| (k.tenant_id, v))
+        .map(|(a, b, c)| (a.tenant_id, b, c))
         .collect())
 }