Merge branch 'stable'

Conflicts:
	docs/rabbitmq.config.example

1 files changed, 9 insertions, 6 deletions

diff --git a/src/rabbit_variable_queue.erl b/src/rabbit_variable_queue.erl
index 4d61bb4b03..ac3d60bb11 100644
--- a/src/rabbit_variable_queue.erl
+++ b/src/rabbit_variable_queue.erl
@@ -189,12 +189,12 @@
 %% (betas+gammas+delta)/(target_ram_count+betas+gammas+delta). I.e. as
 %% the target_ram_count shrinks to 0, so must betas and gammas.
 %%
-%% The conversion of betas to gammas is done in batches of at least
-%% ?IO_BATCH_SIZE. This value should not be too small, otherwise the
-%% frequent operations on the queues of q2 and q3 will not be
-%% effectively amortised (switching the direction of queue access
-%% defeats amortisation). Note that there is a natural upper bound due
-%% to credit_flow limits on the alpha to beta conversion.
+%% The conversion of betas to deltas is done if there are at least
+%% ?IO_BATCH_SIZE betas in q2 & q3. This value should not be too small,
+%% otherwise the frequent operations on the queues of q2 and q3 will not be
+%% effectively amortised (switching the direction of queue access defeats
+%% amortisation). Note that there is a natural upper bound due to credit_flow
+%% limits on the alpha to beta conversion.
 %%
 %% The conversion from alphas to betas is chunked due to the
 %% credit_flow limits of the msg_store. This further smooths the
@@ -2428,6 +2428,9 @@ reduce_memory_use(State = #vqstate {
         end,
 
     State3 =
+        %% If there are more messages with their queue position held in RAM,
+        %% a.k.a. betas, in Q2 & Q3 than IoBatchSize,
+        %% write their queue position to disk, a.k.a. push_betas_to_deltas
         case chunk_size(?QUEUE:len(Q2) + ?QUEUE:len(Q3),
                         permitted_beta_count(State1)) of
             S2 when S2 >= IoBatchSize ->