osd: PgPriorSet: simplify (and change) CRASHED logic

Any single OSD from a given interval surviving is sufficient to ensure
that an ACKed write during that interval was committed to disk.

Currently, at least.

In any case, update the prior set calculation to reflect that.  Also
make the survival conditional a bit smarter, to include both last_clean
interval (from the OSDs previous interval of up-ness) as well as the
current interval [up_from..up_thru).

Signed-off-by: Sage Weil <sage@newdream.net>

diff --git a/src/osd/PG.cc b/src/osd/PG.cc
index b9ef3e39ade19d629aacc7ad54810184c2dfc350..1173b79b8f53a5bf10085eed51fd913f13ba86ac 100644 (file)
--- a/src/osd/PG.cc
+++ b/src/osd/PG.cc
@@ -4906,6 +4906,11 @@ PG::PgPriorSet::PgPriorSet(int whoami,
     bool any_down_now = false;  // any candidates down now (that might have useful data)
     bool any_lost_now = false;  // any candidates lost now (that we will ignore)
 
+    // look at whether any of the osds during this interval survived
+    // past the end of the interval (i.e., didn't crash and
+    // potentially fail to COMMIT a write that it ACKed).
+    bool any_survived_interval = false;
+
     // consider ACTING osds
     for (unsigned i=0; i<interval.acting.size(); i++) {
       int o = interval.acting[i];
@@ -4914,17 +4919,19 @@ PG::PgPriorSet::PgPriorSet(int whoami,
       if (osdmap.exists(o))
        pinfo = &osdmap.get_info(o);
 
-      // if the osd restarted after this interval but is not known to have
-      // cleanly survived through this interval, we mark the pg crashed.
-      if (pinfo && (pinfo->up_from > interval.last &&
-                   !(pinfo->last_clean_first <= interval.first &&
-                     pinfo->last_clean_last >= interval.last))) {
+      // does this osd appear to have survived through the end of the
+      // interval?
+      if (pinfo && ((pinfo->up_from <= interval.first &&
+                    pinfo->up_thru > interval.last) ||            // most recently
+                   (pinfo->up_from > interval.last &&
+                    pinfo->last_clean_first <= interval.first &&
+                    pinfo->last_clean_last >= interval.last))) {  // previous osd interval
        dout(10) << "build_prior  prior osd." << o
                 << " up_from " << pinfo->up_from
                 << " and last clean interval "
                 << pinfo->last_clean_first << "-" << pinfo->last_clean_last
-                << " does not include us" << dendl;
-       crashed = true;
+                << " survived the interval" << dendl;
+       any_survived_interval = true;
       }
 
       if (osdmap.is_up(o)) {
@@ -4959,9 +4966,13 @@ PG::PgPriorSet::PgPriorSet(int whoami,
        }
     }
 
-    if (crashed) {
-      dout(10) << "build_prior  one of " << interval.acting
-              << " possibly crashed, marking pg crashed" << dendl;
+    // if we may have gone rw during this interval, but nobody is
+    // known to have survived through the completion of that interval,
+    // mark the PG crashed so that writers who got ACK but not COMMIT
+    // have a chance to replay their requests and preserve ordering.
+    if (interval.maybe_went_rw && !any_survived_interval) {
+      dout(10) << "build_prior  no acting survived past the interval, marking crashed" << dendl;
+      crashed = true;
     }
   }