storage controller: fix heatmaps getting disabled during shard split (#8197)

## Problem

At the start of do_tenant_shard_split, we drop any secondary location
for the parent shards. The reconciler uses presence of secondary
locations as a condition for enabling heatmaps.

On the pageserver, child shards inherit their configuration from
parents, but the storage controller assumes the child's ObservedState is
the same as the parent's config from the prepare phase. The result is
that some child shards end up with inaccurate ObservedState, and until
something next migrates or restarts, those tenant shards aren't
uploading heatmaps, so their secondary locations are downloading
everything that was resident at the moment of the split (including
ancestor layers which are often cleaned up shortly after the split).

Closes: https://github.com/neondatabase/neon/issues/8189

## Summary of changes

- Use PlacementPolicy to control enablement of heatmap upload, rather
than the literal presence of secondaries in IntentState: this way we
avoid switching them off during shard split
- test: during tenant split test, assert that the child shards have
heatmap uploads enabled.

storage_controller/src/reconciler.rs

@@ -1,6 +1,7 @@
 use crate::pageserver_client::PageserverClient;
 use crate::persistence::Persistence;
 use crate::service;
+use pageserver_api::controller_api::PlacementPolicy;
 use pageserver_api::models::{
     LocationConfig, LocationConfigMode, LocationConfigSecondary, TenantConfig,
 };
@@ -29,6 +30,7 @@ pub(super) struct Reconciler {
     /// of a tenant's state from when we spawned a reconcile task.
     pub(super) tenant_shard_id: TenantShardId,
     pub(crate) shard: ShardIdentity,
+    pub(crate) placement_policy: PlacementPolicy,
     pub(crate) generation: Option<Generation>,
     pub(crate) intent: TargetState,
 
@@ -641,7 +643,7 @@ impl Reconciler {
                 generation,
                 &self.shard,
                 &self.config,
-                !self.intent.secondary.is_empty(),
+                &self.placement_policy,
             );
             match self.observed.locations.get(&node.get_id()) {
                 Some(conf) if conf.conf.as_ref() == Some(&wanted_conf) => {
@@ -801,8 +803,15 @@ pub(crate) fn attached_location_conf(
     generation: Generation,
     shard: &ShardIdentity,
     config: &TenantConfig,
-    has_secondaries: bool,
+    policy: &PlacementPolicy,
 ) -> LocationConfig {
+    let has_secondaries = match policy {
+        PlacementPolicy::Attached(0) | PlacementPolicy::Detached | PlacementPolicy::Secondary => {
+            false
+        }
+        PlacementPolicy::Attached(_) => true,
+    };
+
     LocationConfig {
         mode: LocationConfigMode::AttachedSingle,
         generation: generation.into(),

storage_controller/src/service.rs

@@ -1390,7 +1390,7 @@ impl Service {
                             tenant_shard.generation.unwrap(),
                             &tenant_shard.shard,
                             &tenant_shard.config,
-                            false,
+                            &PlacementPolicy::Attached(0),
                         )),
                     },
                 )]);
@@ -3321,7 +3321,7 @@ impl Service {
                                 generation,
                                 &child_shard,
                                 &config,
-                                matches!(policy, PlacementPolicy::Attached(n) if n > 0),
+                                &policy,
                             )),
                         },
                     );

storage_controller/src/tenant_shard.rs

@@ -908,12 +908,8 @@ impl TenantShard {
                 .generation
                 .expect("Attempted to enter attached state without a generation");
 
-            let wanted_conf = attached_location_conf(
-                generation,
-                &self.shard,
-                &self.config,
-                !self.intent.secondary.is_empty(),
-            );
+            let wanted_conf =
+                attached_location_conf(generation, &self.shard, &self.config, &self.policy);
             match self.observed.locations.get(&node_id) {
                 Some(conf) if conf.conf.as_ref() == Some(&wanted_conf) => {}
                 Some(_) | None => {
@@ -1099,6 +1095,7 @@ impl TenantShard {
         let mut reconciler = Reconciler {
             tenant_shard_id: self.tenant_shard_id,
             shard: self.shard,
+            placement_policy: self.policy.clone(),
             generation: self.generation,
             intent: reconciler_intent,
             detach,

test_runner/regress/test_sharding.py

@@ -542,6 +542,13 @@ def test_sharding_split_smoke(
             for k, v in non_default_tenant_config.items():
                 assert config.effective_config[k] == v
 
+            # Check that heatmap uploads remain enabled after shard split
+            # (https://github.com/neondatabase/neon/issues/8189)
+            assert (
+                config.effective_config["heatmap_period"]
+                and config.effective_config["heatmap_period"] != "0s"
+            )
+
     # Validate pageserver state: expect every child shard to have an attached and secondary location
     (total, attached) = get_node_shard_counts(env, tenant_ids=[tenant_id])
     assert sum(attached.values()) == split_shard_count