From 46fd22bc2a1eb42cd26353b0bea2862c2b5ec5ea Mon Sep 17 00:00:00 2001
From: Matthew Sackman <matthew@rabbitmq.com>
Date: Fri, 30 Sep 2011 17:52:01 +0100
Subject: Avoid delta's low end extending beyond the low end of q3

---
 src/rabbit_variable_queue.erl | 37 +++++++++++++++++++++----------------
 1 file changed, 21 insertions(+), 16 deletions(-)

diff --git a/src/rabbit_variable_queue.erl b/src/rabbit_variable_queue.erl
index 0c3ac4f7..a9b78be9 100644
--- a/src/rabbit_variable_queue.erl
+++ b/src/rabbit_variable_queue.erl
@@ -912,6 +912,8 @@ combine_deltas(#delta { start_seq_id = StartLow,
         andalso ((StartLow + Count) =< EndHigh),
     #delta { start_seq_id = StartLow, count = Count, end_seq_id = EndHigh }.
 
+combine_deltas_flip(A, B) -> combine_deltas(B, A).
+
 beta_fold(Fun, Init, Q) -> ?QUEUE:queue_fold(Fun, Init, Q).
 
 update_rate(Now, Then, Count, {OThen, OCount}) ->
@@ -1680,11 +1682,11 @@ push_betas_to_deltas(Quota,
                                         ram_index_count = RamIndexCount }) ->
     {Quota1, Delta2, Q2a, RamIndexCount2, IndexState2} =
         push_betas_to_deltas(fun (Q2MinSeqId) -> Q2MinSeqId end,
-                             fun ?QUEUE:out/1, Quota, Q2,
+                             fun ?QUEUE:out/1, fun combine_deltas/2, Quota, Q2,
                              RamIndexCount, IndexState),
     {_Quota2, Delta3, Q3a, RamIndexCount3, IndexState3} =
         push_betas_to_deltas(fun rabbit_queue_index:next_segment_boundary/1,
-                             fun ?QUEUE:out_r/1, Quota1, Q3,
+                             fun ?QUEUE:out_r/1, fun combine_deltas_flip/2, Quota1, Q3,
                              RamIndexCount2, IndexState2),
     Delta4 = combine_deltas(Delta3, combine_deltas(Delta, Delta2)),
     State #vqstate { q2              = Q2a,
@@ -1693,7 +1695,7 @@ push_betas_to_deltas(Quota,
                      index_state     = IndexState3,
                      ram_index_count = RamIndexCount3 }.
 
-push_betas_to_deltas(LimitFun, Generator, Quota, Q, RamIndexCount, IndexState) ->
+push_betas_to_deltas(LimitFun, Generator, Combine, Quota, Q, RamIndexCount, IndexState) ->
     case ?QUEUE:out(Q) of
         {empty, _Q} ->
             {Quota, ?BLANK_DELTA, Q, RamIndexCount, IndexState};
@@ -1702,26 +1704,26 @@ push_betas_to_deltas(LimitFun, Generator, Quota, Q, RamIndexCount, IndexState) -
             Limit = LimitFun(MinSeqId),
             case MaxSeqId < Limit of
                 true  -> {Quota, ?BLANK_DELTA, Q, RamIndexCount, IndexState};
-                false -> {Len, Qc, RamIndexCount1, IndexState1} =
-                             push_betas_to_deltas(Generator, Limit, Quota, Q, 0,
-                                                  RamIndexCount, IndexState),
-                         {Quota - Len, #delta { start_seq_id = Limit,
-                                                count        = Len,
-                                                end_seq_id   = MaxSeqId + 1 },
+                false -> {Delta, Qc, RamIndexCount1, IndexState1} =
+                             push_betas_to_deltas(
+                               Generator, Combine, Limit, Quota, ?BLANK_DELTA,
+                               Q, RamIndexCount, IndexState),
+                         {Quota - Delta #delta.count, Delta,
                           Qc, RamIndexCount1, IndexState1}
             end
     end.
 
-push_betas_to_deltas(_Generator, _Limit, 0, Q, Count, RamIndexCount, IndexState) ->
-    {Count, Q, RamIndexCount, IndexState};
-push_betas_to_deltas(Generator, Limit, Quota, Q, Count, RamIndexCount, IndexState) ->
+push_betas_to_deltas(_Generator, _Combine, _Limit, 0, Delta, Q, RamIndexCount, IndexState) ->
+    {Delta, Q, RamIndexCount, IndexState};
+push_betas_to_deltas(Generator, Combine, Limit, Quota, Delta, Q, RamIndexCount, IndexState) ->
     case Generator(Q) of
         {empty, _Q} ->
-            {Count, Q, RamIndexCount, IndexState};
+            {Delta, Q, RamIndexCount, IndexState};
         {{value, #msg_status { seq_id = SeqId }}, _Qa}
           when SeqId < Limit ->
-            {Count, Q, RamIndexCount, IndexState};
-        {{value, MsgStatus = #msg_status { index_on_disk = IndexOnDisk }}, Qa} ->
+            {Delta, Q, RamIndexCount, IndexState};
+        {{value, MsgStatus = #msg_status { index_on_disk = IndexOnDisk,
+                                           seq_id = SeqId }}, Qa} ->
             {Quota1, RamIndexCount1, IndexState1} =
                 case IndexOnDisk of
                     true  -> {Quota, RamIndexCount, IndexState};
@@ -1731,8 +1733,11 @@ push_betas_to_deltas(Generator, Limit, Quota, Q, Count, RamIndexCount, IndexStat
                                                            IndexState),
                              {Quota - 1, RamIndexCount - 1, IndexState2}
                 end,
+            Delta1 = Combine(Delta, #delta { start_seq_id = SeqId,
+                                             count = 1,
+                                             end_seq_id = SeqId + 1 }),
             push_betas_to_deltas(
-              Generator, Limit, Quota1, Qa, Count + 1, RamIndexCount1, IndexState1)
+              Generator, Combine, Limit, Quota1, Delta1, Qa, RamIndexCount1, IndexState1)
     end.
 
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