radosgw-admin: 'sync status' is not behind if there are no mdlog entries

if remote mdlogs are trimmed prematurely, sync status will report
that it's behind the remote's max-marker even if there are no mdlog
entries to sync

for each behind shard, we fetch the next mdlog entry from the remote. if
we get an empty listing, remove that shard from behind_shards. this
logic now has to run before we print "behind shards:" so that empty
shards aren't listed

Fixes: https://tracker.ceph.com/issues/52091
Signed-off-by: Casey Bodley <cbodley@redhat.com>
(cherry picked from commit 14d43f740d101c8d41a2ced4525bf8efd8c9d943)

diff --git a/src/rgw/rgw_admin.cc b/src/rgw/rgw_admin.cc
index 7928867648e292d03066a4922b33777ac228ec93..20c2494f5f4e98e2844989cd1503a826ffd7d06c 100644 (file)
--- a/src/rgw/rgw_admin.cc
+++ b/src/rgw/rgw_admin.cc
@@ -2003,25 +2003,22 @@ static void get_md_sync_status(list<string>& status)
     }
   }
 
-  int total_behind = shards_behind.size() + (sync_status.sync_info.num_shards - num_inc);
-  if (total_behind == 0) {
-    push_ss(ss, status) << "metadata is caught up with master";
-  } else {
-    push_ss(ss, status) << "metadata is behind on " << total_behind << " shards";
-    
-    push_ss(ss, status) << "behind shards: " << "[" << shards_behind_set << "]";
-
+  // fetch remote log entries to determine the oldest change
+  std::optional<std::pair<int, ceph::real_time>> oldest;
+  if (!shards_behind.empty()) {
     map<int, rgw_mdlog_shard_data> master_pos;
     ret = sync.read_master_log_shards_next(dpp(), sync_status.sync_info.period, shards_behind, &master_pos);
     if (ret < 0) {
       derr << "ERROR: failed to fetch master next positions (" << cpp_strerror(-ret) << ")" << dendl;
     } else {
-      std::optional<std::pair<int, ceph::real_time>> oldest;
-
       for (auto iter : master_pos) {
         rgw_mdlog_shard_data& shard_data = iter.second;
 
-        if (!shard_data.entries.empty()) {
+        if (shard_data.entries.empty()) {
+          // there aren't any entries in this shard, so we're not really behind
+          shards_behind.erase(iter.first);
+          shards_behind_set.erase(iter.first);
+        } else {
           rgw_mdlog_entry& entry = shard_data.entries.front();
           if (!oldest) {
             oldest.emplace(iter.first, entry.timestamp);
@@ -2030,11 +2027,18 @@ static void get_md_sync_status(list<string>& status)
           }
         }
       }
+    }
+  }
 
-      if (oldest) {
-        push_ss(ss, status) << "oldest incremental change not applied: "
-            << oldest->second << " [" << oldest->first << ']';
-      }
+  int total_behind = shards_behind.size() + (sync_status.sync_info.num_shards - num_inc);
+  if (total_behind == 0) {
+    push_ss(ss, status) << "metadata is caught up with master";
+  } else {
+    push_ss(ss, status) << "metadata is behind on " << total_behind << " shards";
+    push_ss(ss, status) << "behind shards: " << "[" << shards_behind_set << "]";
+    if (oldest) {
+      push_ss(ss, status) << "oldest incremental change not applied: "
+          << oldest->second << " [" << oldest->first << ']';
     }
   }