Revert "Merge pull request #7672 from rabbitmq/mk-switch-cq-version-to-2-by-default"

This reverts commit f6e1a6e74bc916e17a26a9fed0549df08a26355b, reversing
changes made to c4d6503cad6666307c1ddc3f67ae3617c1c117b8.

6 files changed, 8 insertions, 19 deletions

diff --git a/deps/rabbit/BUILD.bazel b/deps/rabbit/BUILD.bazel
index 648fd9360b..2ec823b661 100644
--- a/deps/rabbit/BUILD.bazel
+++ b/deps/rabbit/BUILD.bazel
@@ -78,8 +78,6 @@ _APP_ENV = """[
 	                         ]},
 	    {halt_on_upgrade_failure, true},
 	    {ssl_apps, [asn1, crypto, public_key, ssl]},
-	    %% classic queue storage implementation version
-	    {classic_queue_default_version, 2},
 	    %% see rabbitmq-server#114
 	    {mirroring_flow_control, true},
 	    {mirroring_sync_batch_size, 4096},
diff --git a/deps/rabbit/Makefile b/deps/rabbit/Makefile
index 8c49dfb60a..c2700c9090 100644
--- a/deps/rabbit/Makefile
+++ b/deps/rabbit/Makefile
@@ -65,8 +65,6 @@ define PROJECT_ENV
 	                         ]},
 	    {halt_on_upgrade_failure, true},
 	    {ssl_apps, [asn1, crypto, public_key, ssl]},
-	    %% classic queue storage implementation version
-        {classic_queue_default_version, 2},
 	    %% see rabbitmq-server#114
 	    {mirroring_flow_control, true},
 	    {mirroring_sync_batch_size, 4096},
diff --git a/deps/rabbit/priv/schema/rabbit.schema b/deps/rabbit/priv/schema/rabbit.schema
index 3968a4153a..a01ebe4485 100644
--- a/deps/rabbit/priv/schema/rabbit.schema
+++ b/deps/rabbit/priv/schema/rabbit.schema
@@ -2408,7 +2408,7 @@ end}.
 
 {translation, "rabbit.classic_queue_default_version",
     fun(Conf) ->
-        case cuttlefish:conf_get("classic_queue.default_version", Conf, 2) of
+        case cuttlefish:conf_get("classic_queue.default_version", Conf, 1) of
             1 -> 1;
             2 -> 2;
             _ -> cuttlefish:unset()
diff --git a/deps/rabbit/src/rabbit_amqqueue_process.erl b/deps/rabbit/src/rabbit_amqqueue_process.erl
index e113f7d27a..2bb5c4824e 100644
--- a/deps/rabbit/src/rabbit_amqqueue_process.erl
+++ b/deps/rabbit/src/rabbit_amqqueue_process.erl
@@ -470,10 +470,12 @@ init_queue_mode(Mode, State = #q {backing_queue = BQ,
 
 init_queue_version(Version0, State = #q {backing_queue = BQ,
                                          backing_queue_state = BQS}) ->
-    %% When the version is undefined we use the default version 2 starting with
-    %% RabbitMQ 3.12.0.
+    %% When the version is undefined we use the default version 1.
+    %% We want to BQ:set_queue_version in all cases because a v2
+    %% policy might have been deleted, for example, and we want
+    %% the queue to go back to v1.
     Version = case Version0 of
-        undefined -> rabbit_misc:get_env(rabbit, classic_queue_default_version, 2);
+        undefined -> rabbit_misc:get_env(rabbit, classic_queue_default_version, 1);
         _ -> Version0
     end,
     BQS1 = BQ:set_queue_version(Version, BQS),
diff --git a/deps/rabbit/src/rabbit_variable_queue.erl b/deps/rabbit/src/rabbit_variable_queue.erl
index 756db060ce..9cf3af8716 100644
--- a/deps/rabbit/src/rabbit_variable_queue.erl
+++ b/deps/rabbit/src/rabbit_variable_queue.erl
@@ -492,9 +492,8 @@ process_recovery_terms(Terms) ->
 
 queue_version(Q) ->
     Resolve = fun(_, ArgVal) -> ArgVal end,
-    %% If queue-version is undefined, we assume v2 starting with RabbitMQ 3.12.0.
     case rabbit_queue_type_util:args_policy_lookup(<<"queue-version">>, Resolve, Q) of
-        undefined -> rabbit_misc:get_env(rabbit, classic_queue_default_version, 2);
+        undefined -> rabbit_misc:get_env(rabbit, classic_queue_default_version, 1);
         Vsn when is_integer(Vsn) -> Vsn;
         Vsn -> binary_to_integer(Vsn)
     end.
diff --git a/release-notes/3.12.0.md b/release-notes/3.12.0.md
index f2f603c3d4..348071ae8e 100644
--- a/release-notes/3.12.0.md
+++ b/release-notes/3.12.0.md
@@ -109,17 +109,9 @@ in the `3.11.x` release series.
 
    GitHub issue: [#7553](https://github.com/rabbitmq/rabbitmq-server/pull/7553#issuecomment-1463660454)
 
- * Reduced memory footprint, improved memory use predictability and throughput of classic queues (version 2, or CQv2).
+ * Reduced memory footprint, improved memory use predictability and throughput of classic queues.
    This particularly benefits classic queues with longer backlogs.
 
-   Classic queue v2 (CQv2) storage implementation can be enabled for all classic queues
-   using `rabbitmq.conf`:
-
-   ``` ini
-   # uses CQv2 for all classic queues by default
-   classic_queue.default_version = 2
-   ```
-
    GitHub issues: [#4522](https://github.com/rabbitmq/rabbitmq-server/pull/4522), [#7516](https://github.com/rabbitmq/rabbitmq-server/pull/7516)
 
  * Reduced peak memory footprint of quorum queues.