From ed382fff6d115a8180fc44ec7a927834d9162135 Mon Sep 17 00:00:00 2001
From: Jonathan Klabunde Tomer <jkt@signal.org>
Date: Tue, 22 Apr 2025 12:26:56 -0700
Subject: [PATCH] log slot number and shard host of message persister failures

---
 .../textsecuregcm/storage/MessagePersister.java      |  3 ++-
 .../textsecuregcm/storage/MessagesCache.java         | 12 ++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/storage/MessagePersister.java b/service/src/main/java/org/whispersystems/textsecuregcm/storage/MessagePersister.java
index 73cc0ea96..24abea4a7 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/storage/MessagePersister.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/storage/MessagePersister.java
@@ -165,7 +165,8 @@ public class MessagePersister implements Managed {
           persistQueue(maybeAccount.get(), maybeDevice.get());
         } catch (final Exception e) {
           PERSIST_QUEUE_EXCEPTION_METER.increment();
-          logger.warn("Failed to persist queue {}::{}; will schedule for retry", accountUuid, deviceId, e);
+          logger.warn("Failed to persist queue {}::{} (slot {}, shard {}); will schedule for retry",
+              accountUuid, deviceId, slot, messagesCache.shardForSlot(slot), e);
 
           messagesCache.addQueueToPersist(accountUuid, deviceId);
 
diff --git a/service/src/main/java/org/whispersystems/textsecuregcm/storage/MessagesCache.java b/service/src/main/java/org/whispersystems/textsecuregcm/storage/MessagesCache.java
index 109235b0f..c6c82d96d 100644
--- a/service/src/main/java/org/whispersystems/textsecuregcm/storage/MessagesCache.java
+++ b/service/src/main/java/org/whispersystems/textsecuregcm/storage/MessagesCache.java
@@ -15,6 +15,8 @@ import io.lettuce.core.Range;
 import io.lettuce.core.ScoredValue;
 import io.lettuce.core.ZAddArgs;
 import io.lettuce.core.cluster.SlotHash;
+import io.lettuce.core.cluster.models.partitions.ClusterPartitionParser;
+import io.lettuce.core.cluster.models.partitions.Partitions;
 import io.micrometer.core.instrument.Counter;
 import io.micrometer.core.instrument.Metrics;
 import io.micrometer.core.instrument.Tag;
@@ -668,6 +670,16 @@ public class MessagesCache {
         .thenRun(() -> sample.stop(clearQueueTimer));
   }
 
+  // expensive—use for rare error logging only
+  public String shardForSlot(int slot) {
+    try {
+      return redisCluster.withBinaryCluster(
+          connection -> ClusterPartitionParser.parse(connection.sync().clusterNodes()).getPartitionBySlot(slot).getUri().getHost());
+    } catch (Throwable ignored) {
+      return "unknown";
+    }
+  }
+
   int getNextSlotToPersist() {
     return (int) (redisCluster.withCluster(connection -> connection.sync().incr(NEXT_SLOT_TO_PERSIST_KEY))
         % SlotHash.SLOT_COUNT);