storage controller: upload heatmaps at end of shard split

control_plane/attachment_service/src/pageserver_client.rs

@@ -101,6 +101,15 @@ impl PageserverClient {
         )
     }
 
+    pub(crate) async fn tenant_heatmap_upload(&self, tenant_id: TenantShardId) -> Result<()> {
+        measured_request!(
+            "tenant_heatmap_upload",
+            crate::metrics::Method::Post,
+            &self.node_id_label,
+            self.inner.tenant_heatmap_upload(tenant_id).await
+        )
+    }
+
     pub(crate) async fn location_config(
         &self,
         tenant_shard_id: TenantShardId,

control_plane/attachment_service/src/service.rs

@@ -3409,6 +3409,14 @@ impl Service {
                     .join(",")
             );
 
+            // Optimization: publish heatmaps immediately, so that secondary locations can start warming up.
+            for child in child_ids {
+                if let Err(e) = client.tenant_heatmap_upload(*child).await {
+                    // Non-fatal, this is just an optimization
+                    tracing::warn!("Failed to upload child {child} heatmap: {e}");
+                }
+            }
+
             if &response.new_shards != child_ids {
                 // This should never happen: the pageserver should agree with us on how shard splits work.
                 return Err(ApiError::InternalServerError(anyhow::anyhow!(

pageserver/client/src/mgmt_api.rs

@@ -271,6 +271,17 @@ impl Client {
         Ok((status, progress))
     }
 
+    pub async fn tenant_heatmap_upload(&self, tenant_id: TenantShardId) -> Result<()> {
+        let path = reqwest::Url::parse(&format!(
+            "{}/v1/tenant/{}/heatmap_upload",
+            self.mgmt_api_endpoint, tenant_id
+        ))
+        .expect("Cannot build URL");
+
+        self.request(Method::POST, path, ()).await?;
+        Ok(())
+    }
+
     pub async fn location_config(
         &self,
         tenant_shard_id: TenantShardId,