Merge pull request ceph#457 from ceph/wip-paxos

paxos fixes

Reviewed-by: Greg Farnum <[email protected]>
Reviewed-by: Joao Eduardo Luis <[email protected]>

src/common/config_opts.h

@@ -209,6 +209,7 @@ OPTION(paxos_trim_min, OPT_INT, 250)  // number of extra proposals tolerated bef
 OPTION(paxos_trim_max, OPT_INT, 500) // max number of extra proposals to trim at a time
 OPTION(paxos_service_trim_min, OPT_INT, 250) // minimum amount of versions to trigger a trim (0 disables it)
 OPTION(paxos_service_trim_max, OPT_INT, 500) // maximum amount of versions to trim during a single proposal (0 disables it)
+OPTION(paxos_kill_at, OPT_INT, 0)
 OPTION(clock_offset, OPT_DOUBLE, 0) // how much to offset the system clock in Clock.cc
 OPTION(auth_cluster_required, OPT_STR, "cephx")   // required of mon, mds, osd daemons
 OPTION(auth_service_required, OPT_STR, "cephx")   // required by daemons of clients

src/mon/Paxos.cc

@@ -103,11 +103,21 @@ void Paxos::collect(version_t oldpn)
 
   // look for uncommitted value
   if (get_store()->exists(get_name(), last_committed+1)) {
+    version_t v = get_store()->get(get_name(), "pending_v");
+    version_t pn = get_store()->get(get_name(), "pending_pn");
+    if (v && pn && v == last_committed + 1) {
+      uncommitted_pn = pn;
+    } else {
+      dout(10) << "WARNING: no pending_pn on disk, using previous accepted_pn " << accepted_pn
+	       << " and crossing our fingers" << dendl;
+      uncommitted_pn = accepted_pn;
+    }
     uncommitted_v = last_committed+1;
-    uncommitted_pn = accepted_pn;
+
     get_store()->get(get_name(), last_committed+1, uncommitted_value);
     assert(uncommitted_value.length());
     dout(10) << "learned uncommitted " << (last_committed+1)
+	     << " pn " << uncommitted_pn
 	     << " (" << uncommitted_value.length() << " bytes) from myself" 
 	     << dendl;
   }
@@ -164,6 +174,8 @@ void Paxos::handle_collect(MMonPaxos *collect)
   last->last_committed = last_committed;
   last->first_committed = first_committed;
 
+  version_t previous_pn = accepted_pn;
+
   // can we accept this pn?
   if (collect->pn > accepted_pn) {
     // ok, accept it
@@ -198,13 +210,25 @@ void Paxos::handle_collect(MMonPaxos *collect)
   // do we have an accepted but uncommitted value?
   //  (it'll be at last_committed+1)
   bufferlist bl;
-  if (get_store()->exists(get_name(), last_committed+1)) {
+  if (collect->last_committed == last_committed &&
+      get_store()->exists(get_name(), last_committed+1)) {
     get_store()->get(get_name(), last_committed+1, bl);
     assert(bl.length() > 0);
     dout(10) << " sharing our accepted but uncommitted value for " 
 	     << last_committed+1 << " (" << bl.length() << " bytes)" << dendl;
     last->values[last_committed+1] = bl;
-    last->uncommitted_pn = accepted_pn;
+
+    version_t v = get_store()->get(get_name(), "pending_v");
+    version_t pn = get_store()->get(get_name(), "pending_pn");
+    if (v && pn && v == last_committed + 1) {
+      last->uncommitted_pn = pn;
+    } else {
+      // previously we didn't record which pn a value was accepted
+      // under!  use the pn value we just had...  :(
+      dout(10) << "WARNING: no pending_pn on disk, using previous accepted_pn " << previous_pn
+	       << " and crossing our fingers" << dendl;
+      last->uncommitted_pn = previous_pn;
+    }
   }
 
   // send reply
@@ -370,9 +394,13 @@ void Paxos::handle_last(MMonPaxos *last)
     return;
   }
 
+  assert(g_conf->paxos_kill_at != 1);
+
   // store any committed values if any are specified in the message
   store_state(last);
 
+  assert(g_conf->paxos_kill_at != 2);
+
   // do they accept your pn?
   if (last->pn > accepted_pn) {
     // no, try again.
@@ -390,15 +418,23 @@ void Paxos::handle_last(MMonPaxos *last)
 	     << num_last << " peons" << dendl;
 
     // did this person send back an accepted but uncommitted value?
-    if (last->uncommitted_pn &&
-	last->uncommitted_pn > uncommitted_pn) {
-      uncommitted_v = last->last_committed+1;
-      uncommitted_pn = last->uncommitted_pn;
-      uncommitted_value = last->values[uncommitted_v];
-      dout(10) << "we learned an uncommitted value for " << uncommitted_v 
-	       << " pn " << uncommitted_pn
-	       << " " << uncommitted_value.length() << " bytes"
-	       << dendl;
+    if (last->uncommitted_pn) {
+      if (last->uncommitted_pn > uncommitted_pn &&
+	  last->last_committed >= last_committed &&
+	  last->last_committed + 1 >= uncommitted_v) {
+	uncommitted_v = last->last_committed+1;
+	uncommitted_pn = last->uncommitted_pn;
+	uncommitted_value = last->values[uncommitted_v];
+	dout(10) << "we learned an uncommitted value for " << uncommitted_v
+		 << " pn " << uncommitted_pn
+		 << " " << uncommitted_value.length() << " bytes"
+		 << dendl;
+      } else {
+	dout(10) << "ignoring uncommitted value for " << (last->last_committed+1)
+		 << " pn " << last->uncommitted_pn
+		 << " " << last->values[last->last_committed+1].length() << " bytes"
+		 << dendl;
+      }
     }
 
     // is that everyone?
@@ -502,6 +538,10 @@ void Paxos::begin(bufferlist& v)
   MonitorDBStore::Transaction t;
   t.put(get_name(), last_committed+1, new_value);
 
+  // note which pn this pending value is for.
+  t.put(get_name(), "pending_v", last_committed + 1);
+  t.put(get_name(), "pending_pn", accepted_pn);
+
   dout(30) << __func__ << " transaction dump:\n";
   JSONFormatter f(true);
   t.dump(&f);
@@ -516,6 +556,8 @@ void Paxos::begin(bufferlist& v)
 
   get_store()->apply_transaction(t);
 
+  assert(g_conf->paxos_kill_at != 3);
+
   if (mon->get_quorum().size() == 1) {
     // we're alone, take it easy
     commit();
@@ -566,6 +608,8 @@ void Paxos::handle_begin(MMonPaxos *begin)
   assert(begin->pn == accepted_pn);
   assert(begin->last_committed == last_committed);
 
+  assert(g_conf->paxos_kill_at != 4);
+
   // set state.
   state = STATE_UPDATING;
   lease_expire = utime_t();  // cancel lease
@@ -578,6 +622,10 @@ void Paxos::handle_begin(MMonPaxos *begin)
   MonitorDBStore::Transaction t;
   t.put(get_name(), v, begin->values[v]);
 
+  // note which pn this pending value is for.
+  t.put(get_name(), "pending_v", v);
+  t.put(get_name(), "pending_pn", accepted_pn);
+
   dout(30) << __func__ << " transaction dump:\n";
   JSONFormatter f(true);
   t.dump(&f);
@@ -586,6 +634,8 @@ void Paxos::handle_begin(MMonPaxos *begin)
 
   get_store()->apply_transaction(t);
 
+  assert(g_conf->paxos_kill_at != 5);
+
   // reply
   MMonPaxos *accept = new MMonPaxos(mon->get_epoch(), MMonPaxos::OP_ACCEPT,
 				    ceph_clock_now(g_ceph_context));
@@ -620,6 +670,8 @@ void Paxos::handle_accept(MMonPaxos *accept)
   accepted.insert(from);
   dout(10) << " now " << accepted << " have accepted" << dendl;
 
+  assert(g_conf->paxos_kill_at != 6);
+
   // new majority?
   if (accepted.size() == (unsigned)mon->monmap->size()/2+1) {
     // yay, commit!
@@ -643,6 +695,8 @@ void Paxos::handle_accept(MMonPaxos *accept)
     // yay!
     extend_lease();
 
+    assert(g_conf->paxos_kill_at != 10);
+
     finish_round();
 
     // wake people up
@@ -673,6 +727,8 @@ void Paxos::commit()
   //   leader still got a majority and committed with out us.)
   lease_expire = utime_t();  // cancel lease
 
+  assert(g_conf->paxos_kill_at != 7);
+
   MonitorDBStore::Transaction t;
 
   // commit locally
@@ -692,6 +748,8 @@ void Paxos::commit()
 
   get_store()->apply_transaction(t);
 
+  assert(g_conf->paxos_kill_at != 8);
+
   // refresh first_committed; this txn may have trimmed.
   first_committed = get_store()->get(get_name(), "first_committed");
 
@@ -713,6 +771,8 @@ void Paxos::commit()
     mon->messenger->send_message(commit, mon->monmap->get_inst(*p));
   }
 
+  assert(g_conf->paxos_kill_at != 9);
+
   // get ready for a new round.
   new_value.clear();
 

src/mon/Paxos.h

@@ -290,8 +290,9 @@ class Paxos {
    */
   version_t accepted_pn;
   /**
-   * @todo This has something to do with the last_committed version. Not sure
-   *	   about what it entails, tbh.
+   * The last_committed epoch of the leader at the time we accepted the last pn.
+   *
+   * This has NO SEMANTIC MEANING, and is there only for the debug output.
    */
   version_t accepted_pn_from;
   /**
@@ -1114,7 +1115,7 @@ class Paxos {
    * @param t The transaction to which we will append the operations
    * @param bl A bufferlist containing an encoded transaction
    */
-  void decode_append_transaction(MonitorDBStore::Transaction& t,
+  static void decode_append_transaction(MonitorDBStore::Transaction& t,
 				 bufferlist& bl) {
     MonitorDBStore::Transaction vt;
     bufferlist::iterator it = bl.begin();

src/tools/ceph-monstore-tool.cc

@@ -31,6 +31,7 @@
 #include "global/global_init.h"
 #include "os/LevelDBStore.h"
 #include "mon/MonitorDBStore.h"
+#include "mon/Paxos.h"
 #include "common/Formatter.h"
 
 namespace po = boost::program_options;
@@ -246,6 +247,19 @@ int main(int argc, char **argv) {
       goto done;
     }
     bl.write_fd(fd);
+  } else if (cmd == "dump-paxos") {
+    for (version_t v = dstart; v <= dstop; ++v) {
+      bufferlist bl;
+      st.get("paxos", v, bl);
+      if (bl.length() == 0)
+	break;
+      cout << "\n--- " << v << " ---" << std::endl;
+      MonitorDBStore::Transaction tx;
+      Paxos::decode_append_transaction(tx, bl);
+      JSONFormatter f(true);
+      tx.dump(&f);
+      f.flush(cout);
+    }
   } else if (cmd == "dump-trace") {
     if (tfile.empty()) {
       std::cerr << "Need trace_file" << std::endl;