From d1b574a67e8814ec3dcade7199eb3e4ce647dd69 Mon Sep 17 00:00:00 2001
From: ieQu1 <99872536+ieQu1@users.noreply.github.com>
Date: Thu, 4 Jul 2024 01:47:30 +0200
Subject: [PATCH] perf(dslocal): Run heavy-duty operations in a temporary
 process

---
 .../src/emqx_ds_builtin_local.erl             | 76 ++++++++++++++-----
 1 file changed, 55 insertions(+), 21 deletions(-)

diff --git a/apps/emqx_ds_builtin_local/src/emqx_ds_builtin_local.erl b/apps/emqx_ds_builtin_local/src/emqx_ds_builtin_local.erl
index 5fe6eb559..28e307832 100644
--- a/apps/emqx_ds_builtin_local/src/emqx_ds_builtin_local.erl
+++ b/apps/emqx_ds_builtin_local/src/emqx_ds_builtin_local.erl
@@ -46,6 +46,12 @@
     shard_of_message/4
 ]).
 
+%% Internal exports:
+-export([
+    do_next/3,
+    do_delete_next/4
+]).
+
 -export_type([db_opts/0, shard/0, iterator/0, delete_iterator/0]).
 
 -include_lib("emqx_utils/include/emqx_message.hrl").
@@ -295,19 +301,8 @@ update_iterator(DB, Iter0 = #{?tag := ?IT, ?shard := Shard, ?enc := StorageIter0
     end.
 
 -spec next(emqx_ds:db(), iterator(), pos_integer()) -> emqx_ds:next_result(iterator()).
-next(DB, Iter0 = #{?tag := ?IT, ?shard := Shard, ?enc := StorageIter0}, N) ->
-    ShardId = {DB, Shard},
-    T0 = erlang:monotonic_time(microsecond),
-    Result = emqx_ds_storage_layer:next(ShardId, StorageIter0, N, current_timestamp(ShardId)),
-    T1 = erlang:monotonic_time(microsecond),
-    emqx_ds_builtin_metrics:observe_next_time(DB, T1 - T0),
-    case Result of
-        {ok, StorageIter, Batch} ->
-            Iter = Iter0#{?enc := StorageIter},
-            {ok, Iter, Batch};
-        Other ->
-            Other
-    end.
+next(DB, Iter, N) ->
+    with_worker(do_next, [DB, Iter, N]).
 
 -spec get_delete_streams(emqx_ds:db(), emqx_ds:topic_filter(), emqx_ds:time()) ->
     [emqx_ds:ds_specific_delete_stream()].
@@ -347,7 +342,36 @@ make_delete_iterator(DB, ?delete_stream(Shard, InnerStream), TopicFilter, StartT
 
 -spec delete_next(emqx_ds:db(), delete_iterator(), emqx_ds:delete_selector(), pos_integer()) ->
     emqx_ds:delete_next_result(emqx_ds:delete_iterator()).
-delete_next(DB, Iter = #{?tag := ?DELETE_IT, ?shard := Shard, ?enc := StorageIter0}, Selector, N) ->
+delete_next(DB, Iter, Selector, N) ->
+    with_worker(do_delete_next, [DB, Iter, Selector, N]).
+
+%%================================================================================
+%% Internal exports
+%%================================================================================
+
+current_timestamp(ShardId) ->
+    emqx_ds_builtin_local_meta:current_timestamp(ShardId).
+
+-spec do_next(emqx_ds:db(), iterator(), pos_integer()) -> emqx_ds:next_result(iterator()).
+do_next(DB, Iter0 = #{?tag := ?IT, ?shard := Shard, ?enc := StorageIter0}, N) ->
+    ShardId = {DB, Shard},
+    T0 = erlang:monotonic_time(microsecond),
+    Result = emqx_ds_storage_layer:next(ShardId, StorageIter0, N, current_timestamp(ShardId)),
+    T1 = erlang:monotonic_time(microsecond),
+    emqx_ds_builtin_metrics:observe_next_time(DB, T1 - T0),
+    case Result of
+        {ok, StorageIter, Batch} ->
+            Iter = Iter0#{?enc := StorageIter},
+            {ok, Iter, Batch};
+        Other ->
+            Other
+    end.
+
+-spec do_delete_next(emqx_ds:db(), delete_iterator(), emqx_ds:delete_selector(), pos_integer()) ->
+    emqx_ds:delete_next_result(emqx_ds:delete_iterator()).
+do_delete_next(
+    DB, Iter = #{?tag := ?DELETE_IT, ?shard := Shard, ?enc := StorageIter0}, Selector, N
+) ->
     ShardId = {DB, Shard},
     case
         emqx_ds_storage_layer:delete_next(
@@ -362,13 +386,6 @@ delete_next(DB, Iter = #{?tag := ?DELETE_IT, ?shard := Shard, ?enc := StorageIte
             Error
     end.
 
-%%================================================================================
-%% Internal exports
-%%================================================================================
-
-current_timestamp(ShardId) ->
-    emqx_ds_builtin_local_meta:current_timestamp(ShardId).
-
 %%================================================================================
 %% Internal functions
 %%================================================================================
@@ -380,3 +397,20 @@ timeus_to_timestamp(undefined) ->
     undefined;
 timeus_to_timestamp(TimestampUs) ->
     TimestampUs div 1000.
+
+with_worker(F, A) ->
+    Parent = self(),
+    Ref = make_ref(),
+    {_Pid, MRef} = spawn_opt(
+        fun() ->
+            Parent ! {Ref, apply(?MODULE, F, A)}
+        end,
+        [monitor, {min_heap_size, 10000}]
+    ),
+    receive
+        {Ref, Result} ->
+            erlang:demonitor(MRef, [flush]),
+            Result;
+        {'DOWN', MRef, _, _, _, Info} ->
+            {error, unrecoverable, Info}
+    end.