TenantInfo: expose generation number (#6348)

Generally useful when debugging / troubleshooting.

I found this useful when manually duplicating a tenant from a script[^1]
where I can't use `neon_fixtures.Pageserver.tenant_attach`'s automatic
integration with the neon_local's attachment_service.

[^1]: https://github.com/neondatabase/neon/pull/6349

libs/pageserver_api/src/models.rs

@@ -368,6 +368,8 @@ 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>,
 }
 
 #[derive(Serialize, Deserialize, Clone)]
@@ -910,6 +912,7 @@ 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(),
@@ -930,6 +933,7 @@ 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

@@ -267,7 +267,7 @@ async fn calculate_synthetic_size_worker(
             }
         };
 
-        for (tenant_shard_id, tenant_state) in tenants {
+        for (tenant_shard_id, tenant_state, _gen) in tenants {
             if tenant_state != TenantState::Active {
                 continue;
             }

pageserver/src/consumption_metrics/metrics.rs

@@ -196,7 +196,7 @@ 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 || !id.is_zero() {
             None
         } else {

pageserver/src/disk_usage_eviction_task.rs

@@ -633,7 +633,7 @@ 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

@@ -874,11 +874,12 @@ 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>>();
 
@@ -908,6 +909,7 @@ async fn tenant_status(
                 state: state.clone(),
                 current_physical_size: Some(current_physical_size),
                 attachment_status: state.attachment_status(),
+                generation: tenant.generation().into(),
             },
             timelines: tenant.list_timeline_ids(),
         })

pageserver/src/tenant.rs

@@ -1931,6 +1931,10 @@ 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

@@ -1629,8 +1629,8 @@ pub(crate) enum TenantMapListError {
 ///
 /// Get list of tenants, for the mgmt API
 ///
-pub(crate) async fn list_tenants() -> Result<Vec<(TenantShardId, TenantState)>, TenantMapListError>
-{
+pub(crate) async fn list_tenants(
+) -> Result<Vec<(TenantShardId, TenantState, Generation)>, TenantMapListError> {
     let tenants = TENANTS.read().unwrap();
     let m = match &*tenants {
         TenantsMap::Initializing => return Err(TenantMapListError::Initializing),
@@ -1638,7 +1638,9 @@ pub(crate) async fn list_tenants() -> Result<Vec<(TenantShardId, TenantState)>,
     };
     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,
         })