diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/rabbit_variable_queue.erl | 20 |
1 files changed, 11 insertions, 9 deletions
diff --git a/src/rabbit_variable_queue.erl b/src/rabbit_variable_queue.erl index 875765819f..d0336de1cb 100644 --- a/src/rabbit_variable_queue.erl +++ b/src/rabbit_variable_queue.erl @@ -156,13 +156,12 @@ %% (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 exactly +%% 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), nor should it be too big, otherwise -%% converting a batch stalls the queue for too long. Therefore, it -%% must be just right. +%% 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 @@ -294,10 +293,7 @@ %% When we discover that we should write some indices to disk for some %% betas, the IO_BATCH_SIZE sets the number of betas that we must be -%% due to write indices for before we do any work at all. This is both -%% a minimum and a maximum - we don't write fewer than IO_BATCH_SIZE -%% indices out in one go, and we don't write more - we can always come -%% back on the next publish to do more. +%% due to write indices for before we do any work at all. -define(IO_BATCH_SIZE, 2048). %% next power-of-2 after ?CREDIT_DISC_BOUND -define(PERSISTENT_MSG_STORE, msg_store_persistent). -define(TRANSIENT_MSG_STORE, msg_store_transient). @@ -1571,7 +1567,13 @@ reduce_memory_use(State = #vqstate { case chunk_size(?QUEUE:len(Q2) + ?QUEUE:len(Q3), permitted_beta_count(State1)) of S2 when S2 >= ?IO_BATCH_SIZE -> - push_betas_to_deltas(?IO_BATCH_SIZE, State1); + %% There is an implicit, but subtle, upper bound here. We + %% may shuffle a lot of messages from Q2/3 into delta, but + %% the number of these that require any disk operation, + %% namely index writing, i.e. messages that are genuine + %% betas and not gammas, is bounded by the credit_flow + %% limiting of the alpha->beta conversion above. + push_betas_to_deltas(S2, State1); _ -> State1 end. |