chore(server): Improve malloc-stats output

Now it will print deduplicated lines, shortening the table
dramatically. Also it's now easier to import it into excel.

Signed-off-by: Roman Gershman <roman@dragonflydb.io>

src/server/memory_cmd.cc

@@ -8,6 +8,7 @@
 #include <mimalloc.h>
 
 #include "facade/error.h"
+#include "server/engine_shard_set.h"
 #include "server/server_state.h"
 
 using namespace std;
@@ -22,13 +23,15 @@ void MiStatsCallback(const char* msg, void* arg) {
   absl::StrAppend(str, msg);
 }
 
+// blocksize, reserved, commited, used.
+using BlockKey = std::tuple<size_t, size_t, size_t, size_t>;
+using BlockMap = absl::flat_hash_map<BlockKey, uint64_t>;
+
 bool MiArenaVisit(const mi_heap_t* heap, const mi_heap_area_t* area, void* block, size_t block_size,
                   void* arg) {
-  string* str = (string*)arg;
-
-  absl::StrAppend(str, "block_size ", block_size, ", reserved ",
-                  area->reserved, ", comitted ", area->committed,
-                  ", used: ", area->used * block_size, "\n");
+  BlockMap* bmap = (BlockMap*)arg;
+  BlockKey bkey{block_size, area->reserved, area->committed, area->used * block_size};
+  (*bmap)[bkey]++;
 
   return true;
 };
@@ -44,25 +47,35 @@ void MemoryCmd::Run(CmdArgList args) {
     // dummy output, in practice not implemented yet.
     return (*cntx_)->SendLong(1);
   } else if (sub_cmd == "MALLOC-STATS") {
-    return MallocStats();
+    string res = shard_set->pool()->at(0)->AwaitBrief([this] { return MallocStats(); });
+    return (*cntx_)->SendBulkString(res);
   }
 
   string err = UnknownSubCmd(sub_cmd, "MEMORY");
   return (*cntx_)->SendError(err, kSyntaxErrType);
 }
 
-void MemoryCmd::MallocStats() {
+string MemoryCmd::MallocStats() {
   string str;
   absl::StrAppend(&str, "___ Begin mimalloc statistics ___\n");
   mi_stats_print_out(MiStatsCallback, &str);
 
   absl::StrAppend(&str, "\nArena statistics from a single thread:\n");
+  absl::StrAppend(&str, "Count BlockSize Reserved Committed Used\n");
+
   mi_heap_t* data_heap = ServerState::tlocal()->data_heap();
-  mi_heap_visit_blocks(data_heap, false /* visit all blocks*/, MiArenaVisit, &str);
+  BlockMap block_map;
+
+  mi_heap_visit_blocks(data_heap, false /* visit all blocks*/, MiArenaVisit, &block_map);
+
+  for (const auto& k_v : block_map) {
+    absl::StrAppend(&str, k_v.second, " ", get<0>(k_v.first), " ", get<1>(k_v.first), " ",
+                    get<2>(k_v.first), " ", get<3>(k_v.first), "\n");
+  }
 
   absl::StrAppend(&str, "--- End mimalloc statistics ---\n");
 
-  return (*cntx_)->SendBulkString(str);
+  return str;
 }
 
 }  // namespace dfly

src/server/memory_cmd.h

@@ -17,7 +17,7 @@ class MemoryCmd {
   void Run(CmdArgList args);
 
  private:
-  void MallocStats();
+  std::string MallocStats();
 
   ServerFamily& sf_;
   ConnectionContext* cntx_;