feat: add defragment command (#3003)

* feat: add defragment command and improve auto defragmentation algorithm

src/server/dragonfly_test.cc

@@ -23,6 +23,7 @@ extern "C" {
 #include "server/test_utils.h"
 
 ABSL_DECLARE_FLAG(float, mem_defrag_threshold);
+ABSL_DECLARE_FLAG(uint32_t, mem_defrag_check_sec_interval);
 ABSL_DECLARE_FLAG(std::vector<std::string>, rename_command);
 ABSL_DECLARE_FLAG(double, oom_deny_ratio);
 ABSL_DECLARE_FLAG(bool, lua_resp2_legacy_float);
@@ -641,7 +642,9 @@ TEST_F(DefragDflyEngineTest, TestDefragOption) {
     GTEST_SKIP() << "Defragmentation via idle task is only supported in io uring";
   }
 
-  absl::SetFlag(&FLAGS_mem_defrag_threshold, 0.02);
+  // mem_defrag_threshold is based on RSS statistic, but we don't count it in the test
+  absl::SetFlag(&FLAGS_mem_defrag_threshold, 0.0);
+  absl::SetFlag(&FLAGS_mem_defrag_check_sec_interval, 0);
   //  Fill data into dragonfly and then check if we have
   //  any location in memory to defrag. See issue #448 for details about this.
   constexpr size_t kMaxMemoryForTest = 1'100'000;

src/server/engine_shard_set.cc

@@ -69,6 +69,9 @@ ABSL_FLAG(string, shard_round_robin_prefix, "",
           "support up to a few hundreds of prefixes. Note: prefix is looked inside hash tags when "
           "cluster mode is enabled.");
 
+ABSL_FLAG(uint32_t, mem_defrag_check_sec_interval, 10,
+          "Number of seconds between every defragmentation necessity check");
+
 namespace dfly {
 
 using namespace tiering::literals;
@@ -222,7 +225,6 @@ EngineShard::Stats& EngineShard::Stats::operator+=(const EngineShard::Stats& o)
 
 void EngineShard::DefragTaskState::UpdateScanState(uint64_t cursor_val) {
   cursor = cursor_val;
-  underutilized_found = false;
   // Once we're done with a db, jump to the next
   if (cursor == kCursorDoneState) {
     dbid++;
@@ -231,7 +233,6 @@ void EngineShard::DefragTaskState::UpdateScanState(uint64_t cursor_val) {
 
 void EngineShard::DefragTaskState::ResetScanState() {
   dbid = cursor = 0u;
-  underutilized_found = false;
 }
 
 // This function checks 3 things:
@@ -241,8 +242,9 @@ void EngineShard::DefragTaskState::ResetScanState() {
 // 3. in case the above is OK, make sure that we have a "gap" between usage and commited memory
 // (control by mem_defrag_waste_threshold flag)
 bool EngineShard::DefragTaskState::CheckRequired() {
-  if (cursor > kCursorDoneState || underutilized_found) {
-    VLOG(2) << "cursor: " << cursor << " and underutilized_found " << underutilized_found;
+  if (is_force_defrag || cursor > kCursorDoneState) {
+    is_force_defrag = false;
+    VLOG(2) << "cursor: " << cursor << " and is_force_defrag " << is_force_defrag;
     return true;
   }
 
@@ -251,20 +253,35 @@ bool EngineShard::DefragTaskState::CheckRequired() {
     return false;
   }
 
-  const std::size_t threshold_mem = memory_per_shard * GetFlag(FLAGS_mem_defrag_threshold);
-  const double waste_threshold = GetFlag(FLAGS_mem_defrag_waste_threshold);
+  const std::size_t global_threshold = max_memory_limit * GetFlag(FLAGS_mem_defrag_threshold);
+  if (global_threshold > rss_mem_current.load(memory_order_relaxed)) {
+    return false;
+  }
+
+  const auto now = time(nullptr);
+  const auto seconds_from_prev_check = now - last_check_time;
+  const auto mem_defrag_interval = GetFlag(FLAGS_mem_defrag_check_sec_interval);
+
+  if (seconds_from_prev_check < mem_defrag_interval) {
+    return false;
+  }
+  last_check_time = now;
 
   ShardMemUsage usage = ReadShardMemUsage(GetFlag(FLAGS_mem_defrag_page_utilization_threshold));
 
-  if (threshold_mem < usage.commited &&
-      usage.wasted_mem > (uint64_t(usage.commited * waste_threshold))) {
+  const double waste_threshold = GetFlag(FLAGS_mem_defrag_waste_threshold);
+  if (usage.wasted_mem > (uint64_t(usage.commited * waste_threshold))) {
     VLOG(1) << "memory issue found for memory " << usage;
-    underutilized_found = true;
+    return true;
   }
 
   return false;
 }
 
+void EngineShard::ForceDefrag() {
+  defrag_state_.is_force_defrag = true;
+}
+
 bool EngineShard::DoDefrag() {
   // --------------------------------------------------------------------------
   // NOTE: This task is running with exclusive access to the shard.
@@ -341,8 +358,7 @@ uint32_t EngineShard::DefragTask() {
   const auto shard_id = db_slice().shard_id();
 
   if (defrag_state_.CheckRequired()) {
-    VLOG(2) << shard_id << ": need to run defrag memory cursor state: " << defrag_state_.cursor
-            << ", underutilzation found: " << defrag_state_.underutilized_found;
+    VLOG(2) << shard_id << ": need to run defrag memory cursor state: " << defrag_state_.cursor;
     if (DoDefrag()) {
       // we didn't finish the scan
       return util::ProactorBase::kOnIdleMaxLevel;

src/server/engine_shard_set.h

@@ -183,11 +183,14 @@ class EngineShard {
 
   TxQueueInfo AnalyzeTxQueue() const;
 
+  void ForceDefrag();
+
  private:
   struct DefragTaskState {
     size_t dbid = 0u;
     uint64_t cursor = 0u;
-    bool underutilized_found = false;
+    time_t last_check_time = 0;
+    bool is_force_defrag = false;
 
     // check the current threshold and return true if
     // we need to do the defragmentation

src/server/memory_cmd.cc

@@ -154,6 +154,14 @@ void MemoryCmd::Run(CmdArgList args) {
     return Track(args);
   }
 
+  if (sub_cmd == "DEFRAGMENT") {
+    shard_set->pool()->DispatchOnAll([this](util::ProactorBase*) {
+      if (auto* shard = EngineShard::tlocal(); shard)
+        shard->ForceDefrag();
+    });
+    return cntx_->SendSimpleString("OK");
+  }
+
   string err = UnknownSubCmd(sub_cmd, "MEMORY");
   return cntx_->SendError(err, kSyntaxErrType);
 }

tools/defrag_mem_test.py

@@ -4,12 +4,13 @@
 import async_timeout
 import sys
 import argparse
-'''
+
+"""
 To install: pip install -r requirements.txt
 
 Run
-dragonfly --mem_defrag_threshold=0.01 --commit_use_threshold=1.2 --mem_utilization_threshold=0.8
-defrag_mem_test.py -k 800000 -v 645
+dragonfly --mem_defrag_threshold=0.01 --mem_defrag_waste_threshold=0.01
+defrag_mem_test.py -k 8000000 -v 645
 
 This program would try to re-create the issue with memory defragmentation.
 See issue number 448 for more details.
@@ -29,7 +30,8 @@
 NOTE:
     If this seems to get stuck please kill it with ctrl+c
     This can happen in case we don't have "defrag_realloc_total > 0"
-'''
+"""
+
 
 class TaskCancel:
     def __init__(self):
@@ -41,37 +43,40 @@ def dont_stop(self):
     def stop(self):
         self.run = False
 
+
 async def run_cmd(connection, cmd, sub_val):
     val = await connection.execute_command(cmd, sub_val)
     return val
 
+
 async def handle_defrag_stats(connection, prev):
     info = await run_cmd(connection, "info", "stats")
     if info is not None:
-        if info['defrag_task_invocation_total'] != prev:
+        if info["defrag_task_invocation_total"] != prev:
             print("--------------------------------------------------------------")
             print(f"defrag_task_invocation_total: {info['defrag_task_invocation_total']:,}")
             print(f"defrag_realloc_total: {info['defrag_realloc_total']:,}")
             print(f"defrag_attempt_total: {info['defrag_attempt_total']:,}")
             print("--------------------------------------------------------------")
             if info["defrag_realloc_total"] > 0:
                 return True, None
-            return False, info['defrag_task_invocation_total']
+            return False, info["defrag_task_invocation_total"]
     return False, None
 
+
 async def memory_stats(connection):
     print("--------------------------------------------------------------")
     info = await run_cmd(connection, "info", "memory")
-    print(f"memory commited: {info['comitted_memory']:,}")
+    # print(f"memory commited: {info['comitted_memory']:,}")
     print(f"memory used: {info['used_memory']:,}")
-    print(f"memory usage ratio: {info['comitted_memory']/info['used_memory']:.2f}")
+    # print(f"memory usage ratio: {info['comitted_memory']/info['used_memory']:.2f}")
     print("--------------------------------------------------------------")
 
 
 async def stats_check(connection, condition):
     try:
-        defrag_task_invocation_total = 0;
-        runs=0
+        defrag_task_invocation_total = 0
+        runs = 0
         while condition.dont_stop():
             await asyncio.sleep(0.3)
             done, d = await handle_defrag_stats(connection, defrag_task_invocation_total)
@@ -101,13 +106,15 @@ async def delete_keys(connection, keys):
     results = await connection.delete(*keys)
     return results
 
+
 def generate_keys(pattern: str, count: int, batch_size: int) -> list:
     for i in range(1, count, batch_size):
         batch = [f"{pattern}{j}" for j in range(i, batch_size + i, 3)]
         yield batch
 
+
 async def mem_cleanup(connection, pattern, num, cond, keys_count):
-    counter=0
+    counter = 0
     for keys in generate_keys(pattern=pattern, count=keys_count, batch_size=950):
         if cond.dont_stop() == False:
             print(f"task number {num} that deleted keys {pattern} finished")
@@ -130,9 +137,17 @@ async def run_tasks(pool, key_name, value_size, keys_count):
         tasks = []
         count = 0
         for key in keys:
-            pattern=f"{key}:"
+            pattern = f"{key}:"
             print(f"deleting keys from {pattern}")
-            tasks.append(mem_cleanup(connection=connection, pattern=pattern, num=count, cond=stop_cond, keys_count=int(keys_count)))
+            tasks.append(
+                mem_cleanup(
+                    connection=connection,
+                    pattern=pattern,
+                    num=count,
+                    cond=stop_cond,
+                    keys_count=int(keys_count),
+                )
+            )
             count += 1
         monitor_task = asyncio.create_task(stats_check(connection, stop_cond))
         total = await asyncio.gather(*tasks, return_exceptions=True)
@@ -147,29 +162,40 @@ async def run_tasks(pool, key_name, value_size, keys_count):
 
 
 def connect_and_run(key_name, value_size, keys_count, host="localhost", port=6379):
-    async_pool = aioredis.ConnectionPool(host=host, port=port,
-                                         db=0, decode_responses=True, max_connections=16)
+    async_pool = aioredis.ConnectionPool(
+        host=host, port=port, db=0, decode_responses=True, max_connections=16
+    )
 
     loop = asyncio.new_event_loop()
-    success = loop.run_until_complete(run_tasks(pool=async_pool, key_name=key_name, value_size=value_size, keys_count=keys_count))
+    success = loop.run_until_complete(
+        run_tasks(pool=async_pool, key_name=key_name, value_size=value_size, keys_count=keys_count)
+    )
     return success
 
 
 if __name__ == "__main__":
-    parser = argparse.ArgumentParser(description='active memory testing', formatter_class=argparse.ArgumentDefaultsHelpFormatter)
-    parser.add_argument('-k', '--keys', type=int, default=800000, help='total number of keys')
-    parser.add_argument('-v', '--value_size', type=int, default=645, help='size of the values')
-    parser.add_argument('-n', '--key_name', type=str, default="key-for-testing", help='the base key name')
-    parser.add_argument('-s', '--server', type=str, default="localhost", help='server host name')
-    parser.add_argument('-p', '--port', type=int, default=6379, help='server port number')
+    parser = argparse.ArgumentParser(
+        description="active memory testing", formatter_class=argparse.ArgumentDefaultsHelpFormatter
+    )
+    parser.add_argument("-k", "--keys", type=int, default=800000, help="total number of keys")
+    parser.add_argument("-v", "--value_size", type=int, default=645, help="size of the values")
+    parser.add_argument(
+        "-n", "--key_name", type=str, default="key-for-testing", help="the base key name"
+    )
+    parser.add_argument("-s", "--server", type=str, default="localhost", help="server host name")
+    parser.add_argument("-p", "--port", type=int, default=6379, help="server port number")
     args = parser.parse_args()
     keys_num = args.keys
     key_name = args.key_name
     value_size = args.value_size
     host = args.server
     port = args.port
-    print(f"running key deletion on {host}:{port} for keys {key_name} value size of {value_size} and number of keys {keys_num}")
-    result = connect_and_run(key_name=key_name, value_size=value_size, keys_count=keys_num, host=host, port=port)
+    print(
+        f"running key deletion on {host}:{port} for keys {key_name} value size of {value_size} and number of keys {keys_num}"
+    )
+    result = connect_and_run(
+        key_name=key_name, value_size=value_size, keys_count=keys_num, host=host, port=port
+    )
     if result == True:
         print("finished successfully")
     else: