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>

diff --git a/src/rgw/rgw_admin.cc b/src/rgw/rgw_admin.cc
index b202e9d9c31dbb069216d299e5f43ca470901025..d0608618eac9a6eb95d9432abcf385541b3abda7 100644 (file)
--- a/src/rgw/rgw_admin.cc
+++ b/src/rgw/rgw_admin.cc
@@ -1987,25 +1987,22 @@ 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);
@@ -2014,11 +2011,18 @@ 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 << ']';
     }
   }