PG::find_best_info: fix log_tail component

The previous logic should have kept the current best info if it found a
replica which best could log-recover, but p couldn't.  However, the
continue in that loop advanced the inner loop instead of the outer loop
allowing the primary case to take over in cases where best had a longer
tail.  Instead, we will prefer the longer tail regardless of the other
infos to simplify the logic.

Fixes: #7755
Signed-off-by: Samuel Just <sam.just@inktank.com>

diff --git a/src/osd/PG.cc b/src/osd/PG.cc
index a4029f82a0bc8443d1097b93a290c39833af798c..7829e8495fc9da25d2753f4b7f350de795e24484 100644 (file)
--- a/src/osd/PG.cc
+++ b/src/osd/PG.cc
@@ -895,24 +895,15 @@ map<pg_shard_t, pg_info_t>::const_iterator PG::find_best_info(
        continue;
       }
     }
-    // Prefer longer tail if it brings another peer into contiguity
-    for (map<pg_shard_t, pg_info_t>::const_iterator q = infos.begin();
-        q != infos.end();
-        ++q) {
-      if (q->second.is_incomplete())
-       continue;  // don't care about log contiguity
-      if (q->second.last_update < best->second.log_tail &&
-         q->second.last_update >= p->second.log_tail) {
-       dout(10) << "calc_acting prefer osd." << p->first
-                << " because it brings osd." << q->first << " into log contiguity" << dendl;
-       best = p;
-       continue;
-      }
-      if (q->second.last_update < p->second.log_tail &&
-         q->second.last_update >= best->second.log_tail) {
-       continue;
-      }
+
+    // Prefer longer tail
+    if (p->second.log_tail > best->second.log_tail) {
+      continue;
+    } else if (p->second.log_tail < best->second.log_tail) {
+      best = p;
+      continue;
     }
+
     // prefer current primary (usually the caller), all things being equal
     if (p->first == pg_whoami) {
       dout(10) << "calc_acting prefer osd." << p->first