From 47f5bcf2bcef94e6cdc9a9ec1b07f8bf94bf1c11 Mon Sep 17 00:00:00 2001
From: Erik Grinaker <erik@neon.tech>
Date: Wed, 2 Apr 2025 14:55:15 +0200
Subject: [PATCH] pageserver: don't periodically flush layers for stale
 attachments (#11317)

## Problem

Tenants in attachment state `Stale` can't upload layers, and don't run
compaction, but still do periodic L0 layer flushes in the tenant
housekeeping loop. If the tenant remains stuck in stale mode, this
causes a large buildup of L0 layers, causing logging, metrics increases,
and possibly alerts.

Resolves #11245.

## Summary of changes

Don't perform periodic layer flushes in stale attachment state.
---
 pageserver/src/tenant.rs | 26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/pageserver/src/tenant.rs b/pageserver/src/tenant.rs
index f1dbb274b9..15853133d6 100644
--- a/pageserver/src/tenant.rs
+++ b/pageserver/src/tenant.rs
@@ -3248,17 +3248,23 @@ impl Tenant {
     async fn housekeeping(&self) {
         // Call through to all timelines to freeze ephemeral layers as needed. This usually happens
         // during ingest, but we don't want idle timelines to hold open layers for too long.
-        let timelines = self
-            .timelines
-            .lock()
-            .unwrap()
-            .values()
-            .filter(|tli| tli.is_active())
-            .cloned()
-            .collect_vec();
+        //
+        // We don't do this if the tenant can't upload layers (i.e. it's in stale attachment mode).
+        // We don't run compaction in this case either, and don't want to keep flushing tiny L0
+        // layers that won't be compacted down.
+        if self.tenant_conf.load().location.may_upload_layers_hint() {
+            let timelines = self
+                .timelines
+                .lock()
+                .unwrap()
+                .values()
+                .filter(|tli| tli.is_active())
+                .cloned()
+                .collect_vec();
 
-        for timeline in timelines {
-            timeline.maybe_freeze_ephemeral_layer().await;
+            for timeline in timelines {
+                timeline.maybe_freeze_ephemeral_layer().await;
+            }
         }
 
         // Shut down walredo if idle.