diff --git a/.github/workflows/docker-release.yml b/.github/workflows/docker-release.yml
index eeca2b4..7b28d4f 100644
--- a/.github/workflows/docker-release.yml
+++ b/.github/workflows/docker-release.yml
@@ -47,6 +47,8 @@ jobs:
       with:
         context: .
         platforms: linux/amd64,linux/arm64
+        build-args: |
+          QEMU_CPU='help'
         push: ${{ github.event_name != 'pull_request' }}
         tags: |
           ghcr.io/${{ github.actor }}/dragonfly-ubuntu:latest
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 62aa38d..5d7dae4 100755
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -15,7 +15,6 @@ set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/helio/cmake" ${CMAKE_MODULE_PATH})
 option(BUILD_SHARED_LIBS "Build shared libraries" OFF)
 
-set(Boost_USE_STATIC_LIBS ON)
 include(third_party)
 include(internal)
 
diff --git a/helio b/helio
index a024151..cd13f66 160000
--- a/helio
+++ b/helio
@@ -1 +1 @@
-Subproject commit a024151f24180d493b51909b6853cfd16ae6367d
+Subproject commit cd13f66ea2d6b98cfa3f5441fd151f41f9dc6966
diff --git a/src/server/common.cc b/src/server/common.cc
index 403bf35..c37bf6e 100644
--- a/src/server/common.cc
+++ b/src/server/common.cc
@@ -19,6 +19,7 @@ thread_local ServerState ServerState::state_;
 atomic_uint64_t used_mem_peak(0);
 atomic_uint64_t used_mem_current(0);
 unsigned kernel_version = 0;
+size_t max_memory_limit = 0;
 
 ServerState::ServerState() {
 }
@@ -114,12 +115,12 @@ bool ParseHumanReadableBytes(std::string_view str, int64_t* num_bytes) {
 #define ADD(x) (x) += o.x
 
 TieredStats& TieredStats::operator+=(const TieredStats& o) {
-  static_assert(sizeof(TieredStats) == 24);
+  static_assert(sizeof(TieredStats) == 32);
 
   ADD(external_reads);
   ADD(external_writes);
   ADD(storage_capacity);
-
+  ADD(storage_reserved);
   return *this;
 }
 
diff --git a/src/server/common.h b/src/server/common.h
index f7777b4..4100127 100644
--- a/src/server/common.h
+++ b/src/server/common.h
@@ -75,6 +75,9 @@ struct TieredStats {
   size_t external_writes = 0;
   size_t storage_capacity = 0;
 
+  // how much was reserved by actively stored items.
+  size_t storage_reserved = 0;
+
   TieredStats& operator+=(const TieredStats&);
 };
 
@@ -96,6 +99,7 @@ bool ParseHumanReadableBytes(std::string_view str, int64_t* num_bytes);
 // Cached values, updated frequently to represent the correct state of the system.
 extern std::atomic_uint64_t used_mem_peak;
 extern std::atomic_uint64_t used_mem_current;
+extern size_t max_memory_limit;
 
 // version 5.11 maps to 511 etc.
 // set upon server start.
diff --git a/src/server/db_slice.cc b/src/server/db_slice.cc
index 31f3692..79457c7 100644
--- a/src/server/db_slice.cc
+++ b/src/server/db_slice.cc
@@ -86,20 +86,32 @@ class PrimeEvictionPolicy {
 
 #define ADD(x) (x) += o.x
 
+PerDbStats& PerDbStats::operator+=(const PerDbStats& o) {
+  constexpr size_t kDbSz = sizeof(PerDbStats);
+  static_assert(kDbSz == 56);
+
+  ADD(inline_keys);
+  ADD(obj_memory_usage);
+  ADD(strval_memory_usage);
+  ADD(listpack_blob_cnt);
+  ADD(listpack_bytes);
+  ADD(external_entries);
+  ADD(external_size);
+
+  return *this;
+}
+
 DbStats& DbStats::operator+=(const DbStats& o) {
-  static_assert(sizeof(DbStats) == 80);
+  constexpr size_t kDbSz = sizeof(DbStats);
+  static_assert(kDbSz == 96);
+
+  PerDbStats::operator+=(o);
 
   ADD(key_count);
   ADD(expire_count);
   ADD(bucket_count);
-  ADD(inline_keys);
-
-  ADD(obj_memory_usage);
   ADD(table_mem_usage);
   ADD(small_string_bytes);
-  ADD(listpack_blob_cnt);
-  ADD(listpack_bytes);
-  ADD(external_entries);
 
   return *this;
 }
@@ -150,12 +162,8 @@ auto DbSlice::GetStats() const -> Stats {
     s.db.key_count += db->prime_table.size();
     s.db.bucket_count += db->prime_table.bucket_count();
     s.db.expire_count += db->expire_table.size();
-    s.db.obj_memory_usage += db->stats.obj_memory_usage;
-    s.db.inline_keys += db->stats.inline_keys;
     s.db.table_mem_usage += (db->prime_table.mem_usage() + db->expire_table.mem_usage());
-    s.db.listpack_blob_cnt += db->stats.listpack_blob_cnt;
-    s.db.listpack_bytes += db->stats.listpack_bytes;
-    s.db.external_entries += db->stats.external_entries;
+    s.db += db->stats;
   }
   s.db.small_string_bytes = CompactObj::GetStats().small_string_bytes;
 
@@ -275,7 +283,11 @@ auto DbSlice::AddOrFind(DbIndex db_index, string_view key) -> pair<PrimeIterator
       }
 
       // Keep the entry but reset the object.
-      db->stats.obj_memory_usage -= existing->second.MallocUsed();
+      size_t value_heap_size = existing->second.MallocUsed();
+      db->stats.obj_memory_usage -= value_heap_size;
+      if (existing->second.ObjType() == OBJ_STRING)
+        db->stats.obj_memory_usage -= value_heap_size;
+
       existing->second.Reset();
       events_.expired_keys++;
 
@@ -313,8 +325,12 @@ bool DbSlice::Del(DbIndex db_ind, PrimeIterator it) {
     CHECK_EQ(1u, db->mcflag_table.Erase(it->first));
   }
 
+  size_t value_heap_size = it->second.MallocUsed();
   db->stats.inline_keys -= it->first.IsInline();
-  db->stats.obj_memory_usage -= (it->first.MallocUsed() + it->second.MallocUsed());
+  db->stats.obj_memory_usage -= (it->first.MallocUsed() + value_heap_size);
+  if (it->second.ObjType() == OBJ_STRING)
+    db->stats.obj_memory_usage -= value_heap_size;
+
   db->prime_table.Erase(it);
 
   return true;
@@ -413,7 +429,11 @@ pair<PrimeIterator, bool> DbSlice::AddOrFind(DbIndex db_ind, string_view key, Pr
   auto& db = *db_arr_[db_ind];
   auto& new_it = res.first;
 
-  db.stats.obj_memory_usage += obj.MallocUsed();
+  size_t value_heap_size = obj.MallocUsed();
+  db.stats.obj_memory_usage += value_heap_size;
+  if (obj.ObjType() == OBJ_STRING)
+    db.stats.strval_memory_usage += value_heap_size;
+
   new_it->second = std::move(obj);
 
   if (expire_at_ms) {
@@ -514,13 +534,20 @@ void DbSlice::PreUpdate(DbIndex db_ind, PrimeIterator it) {
   for (const auto& ccb : change_cb_) {
     ccb.second(db_ind, ChangeReq{it});
   }
-  db->stats.obj_memory_usage -= it->second.MallocUsed();
+  size_t value_heap_size = it->second.MallocUsed();
+  db->stats.obj_memory_usage -= value_heap_size;
+  if (it->second.ObjType() == OBJ_STRING)
+    db->stats.strval_memory_usage -= value_heap_size;
+
   it.SetVersion(NextVersion());
 }
 
 void DbSlice::PostUpdate(DbIndex db_ind, PrimeIterator it) {
   auto& db = db_arr_[db_ind];
-  db->stats.obj_memory_usage += it->second.MallocUsed();
+  size_t value_heap_size = it->second.MallocUsed();
+  db->stats.obj_memory_usage += value_heap_size;
+  if (it->second.ObjType() == OBJ_STRING)
+    db->stats.strval_memory_usage += value_heap_size;
 }
 
 pair<PrimeIterator, ExpireIterator> DbSlice::ExpireIfNeeded(DbIndex db_ind,
@@ -541,7 +568,10 @@ pair<PrimeIterator, ExpireIterator> DbSlice::ExpireIfNeeded(DbIndex db_ind,
   db->expire_table.Erase(expire_it);
 
   db->stats.inline_keys -= it->first.IsInline();
-  db->stats.obj_memory_usage -= (it->first.MallocUsed() + it->second.MallocUsed());
+  size_t value_heap_size = it->second.MallocUsed();
+  db->stats.obj_memory_usage -= (it->first.MallocUsed() + value_heap_size);
+  if (it->second.ObjType() == OBJ_STRING)
+    db->stats.strval_memory_usage -= value_heap_size;
   db->prime_table.Erase(it);
   ++events_.expired_keys;
 
diff --git a/src/server/db_slice.h b/src/server/db_slice.h
index 0121057..56c37f3 100644
--- a/src/server/db_slice.h
+++ b/src/server/db_slice.h
@@ -20,7 +20,23 @@ namespace dfly {
 
 using facade::OpResult;
 
-struct DbStats {
+struct PerDbStats {
+  // Number of inline keys.
+  uint64_t inline_keys = 0;
+
+  // Object memory usage besides hash-table capacity.
+  // Applies for any non-inline objects.
+  size_t obj_memory_usage = 0;
+  size_t strval_memory_usage = 0;
+  size_t listpack_blob_cnt = 0;
+  size_t listpack_bytes = 0;
+  size_t external_entries = 0;
+  size_t external_size = 0;
+
+  PerDbStats& operator+=(const PerDbStats& o);
+};
+
+struct DbStats : public PerDbStats {
   // number of active keys.
   size_t key_count = 0;
 
@@ -30,23 +46,12 @@ struct DbStats {
   // number of buckets in dictionary (key capacity)
   size_t bucket_count = 0;
 
-  // Number of inline keys.
-  size_t inline_keys = 0;
-
-  // Object memory usage besides hash-table capacity.
-  // Applies for any non-inline objects.
-  size_t obj_memory_usage = 0;
-
   // Memory used by dictionaries.
   size_t table_mem_usage = 0;
 
   size_t small_string_bytes = 0;
 
-  size_t listpack_blob_cnt = 0;
-  size_t listpack_bytes = 0;
-
-  size_t external_entries = 0;
-
+  using PerDbStats::operator+=;
   DbStats& operator+=(const DbStats& o);
 };
 
@@ -65,24 +70,13 @@ class DbSlice {
   void operator=(const DbSlice&) = delete;
 
  public:
+  using PerDbStats = ::dfly::PerDbStats;
+
   struct Stats {
     DbStats db;
     SliceEvents events;
   };
 
-  struct PerDbStats {
-    // Number of inline keys.
-    uint64_t inline_keys = 0;
-
-    // Object memory usage besides hash-table capacity.
-    // Applies for any non-inline objects.
-    size_t obj_memory_usage = 0;
-    size_t listpack_blob_cnt = 0;
-    size_t listpack_bytes = 0;
-    size_t external_entries = 0;
-  };
-
-
   DbSlice(uint32_t index, EngineShard* owner);
   ~DbSlice();
 
diff --git a/src/server/dfly_main.cc b/src/server/dfly_main.cc
index 09c320d..51abcd2 100644
--- a/src/server/dfly_main.cc
+++ b/src/server/dfly_main.cc
@@ -89,8 +89,12 @@ int main(int argc, char* argv[]) {
     LOG(INFO) << "Found " << HumanReadableNumBytes(available)
               << " available memory. Setting maxmemory to " << HumanReadableNumBytes(maxmemory);
     FLAGS_maxmemory = maxmemory;
+  } else {
+    LOG(INFO) << "Max memory limit is: " << HumanReadableNumBytes(FLAGS_maxmemory);
   }
 
+  dfly::max_memory_limit = FLAGS_maxmemory;
+
   if (FLAGS_use_large_pages) {
     mi_option_enable(mi_option_large_os_pages);
   }
diff --git a/src/server/io_mgr.cc b/src/server/io_mgr.cc
index c753567..07283ef 100644
--- a/src/server/io_mgr.cc
+++ b/src/server/io_mgr.cc
@@ -5,6 +5,7 @@
 #include "server/io_mgr.h"
 
 #include <fcntl.h>
+#include <mimalloc.h>
 
 #include "base/logging.h"
 #include "facade/facade_types.h"
@@ -21,6 +22,15 @@ using uring::FiberCall;
 using uring::Proactor;
 namespace this_fiber = ::boost::this_fiber;
 
+namespace {
+
+constexpr inline size_t alignup(size_t num, size_t align) {
+  size_t amask = align - 1;
+  return (num + amask) & (~amask);
+}
+
+}  // namespace
+
 IoMgr::IoMgr() {
   flags_val = 0;
 }
@@ -99,6 +109,27 @@ error_code IoMgr::WriteAsync(size_t offset, string_view blob, WriteCb cb) {
 }
 
 error_code IoMgr::Read(size_t offset, io::MutableBytes dest) {
+  DCHECK(!dest.empty());
+
+  if (FLAGS_backing_file_direct) {
+    size_t read_offs = offset & ~4095ULL;
+    size_t end_range = alignup(offset + dest.size(), 4096);
+    size_t space_needed = end_range - read_offs;
+    DCHECK_EQ(0u, space_needed % 4096);
+
+    uint8_t* space = (uint8_t*)mi_malloc_aligned(space_needed, 4096);
+    iovec v{.iov_base = space, .iov_len = space_needed};
+    error_code ec = backing_file_->Read(&v, 1, read_offs, 0);
+    if (ec) {
+      mi_free(space);
+      return ec;
+    }
+
+    memcpy(dest.data(), space + offset - read_offs, dest.size());
+    mi_free_size_aligned(space, space_needed, 4096);
+    return ec;
+  }
+
   iovec v{.iov_base = dest.data(), .iov_len = dest.size()};
   return backing_file_->Read(&v, 1, offset, 0);
 }
diff --git a/src/server/io_mgr.h b/src/server/io_mgr.h
index c8f05ae..d09df6f 100644
--- a/src/server/io_mgr.h
+++ b/src/server/io_mgr.h
@@ -36,7 +36,8 @@ class IoMgr {
   std::error_code WriteAsync(size_t offset, std::string_view blob, WriteCb cb);
   std::error_code Read(size_t offset, io::MutableBytes dest);
 
-  size_t Size() const {
+  // Total file span
+  size_t Span() const {
     return sz_;
   }
 
diff --git a/src/server/server_family.cc b/src/server/server_family.cc
index 7b0a284..005d64f 100644
--- a/src/server/server_family.cc
+++ b/src/server/server_family.cc
@@ -515,6 +515,7 @@ tcp_port:)";
     append("num_entries:", m.db.key_count);
     append("inline_keys:", m.db.inline_keys);
     append("small_string_bytes:", m.db.small_string_bytes);
+    append("strval_bytes:", m.db.strval_memory_usage);
     append("listpack_blobs:", m.db.listpack_blob_cnt);
     append("listpack_bytes:", m.db.listpack_bytes);
   }
@@ -540,10 +541,12 @@ tcp_port:)";
   }
 
   if (should_enter("TIERED", true)) {
-    ADD_HEADER("# TIERED_STORAGE");
+    ADD_HEADER("# TIERED");
     append("external_entries:", m.db.external_entries);
+    append("external_bytes:", m.db.external_size);
     append("external_reads:", m.tiered_stats.external_reads);
     append("external_writes:", m.tiered_stats.external_writes);
+    append("external_reserved:", m.tiered_stats.storage_reserved);
     append("external_capacity:", m.tiered_stats.storage_capacity);
   }
 
diff --git a/src/server/string_family.cc b/src/server/string_family.cc
index 8cd6022..e7e54c7 100644
--- a/src/server/string_family.cc
+++ b/src/server/string_family.cc
@@ -136,7 +136,7 @@ OpResult<void> SetCmd::Set(const SetParams& params, std::string_view key, std::s
   EngineShard* shard = db_slice_.shard_owner();
 
   if (shard->tiered_storage()) {  // external storage enabled.
-    if (value.size() >= 64 && value.size() < 2_MB) {
+    if (value.size() >= 64) {
       shard->tiered_storage()->UnloadItem(params.db_index, it);
     }
   }
@@ -869,7 +869,6 @@ OpResult<string> StringFamily::OpGet(const OpArgs& op_args, string_view key) {
     auto [offset, size] = pv.GetExternalPtr();
     val.resize(size);
 
-    // TODO: can not work with O_DIRECT
     error_code ec = tiered->Read(offset, size, val.data());
     CHECK(!ec) << "TBD: " << ec;
   } else {
diff --git a/src/server/tiered_storage.cc b/src/server/tiered_storage.cc
index b9bfbd4..18a4659 100644
--- a/src/server/tiered_storage.cc
+++ b/src/server/tiered_storage.cc
@@ -52,6 +52,7 @@ struct EntryHash {
 };
 
 struct TieredStorage::ActiveIoRequest {
+  size_t file_offset;
   char* block_ptr;
 
   // entry -> offset
@@ -59,7 +60,7 @@ struct TieredStorage::ActiveIoRequest {
                       mi_stl_allocator<std::pair<const IndexKey, size_t>>>*/
   absl::flat_hash_map<IndexKey, size_t, EntryHash, std::equal_to<>> entries;
 
-  ActiveIoRequest(size_t sz) {
+  ActiveIoRequest(size_t file_offs, size_t sz) : file_offset(file_offs) {
     DCHECK_EQ(0u, sz % 4096);
     block_ptr = (char*)mi_malloc_aligned(sz, 4096);
     DCHECK_EQ(0, intptr_t(block_ptr) % 4096);
@@ -70,7 +71,7 @@ struct TieredStorage::ActiveIoRequest {
   }
 };
 
-void TieredStorage::SendIoRequest(size_t offset, size_t req_size, ActiveIoRequest* req) {
+void TieredStorage::SendIoRequest(size_t req_size, ActiveIoRequest* req) {
 #if 1
   // static string tmp(4096, 'x');
   // string_view sv{tmp};
@@ -80,7 +81,7 @@ void TieredStorage::SendIoRequest(size_t offset, size_t req_size, ActiveIoReques
       [this] { return num_active_requests_ <= FLAGS_tiered_storage_max_pending_writes; });
 
   auto cb = [this, req](int res) { FinishIoRequest(res, req); };
-  io_mgr_.WriteAsync(offset, sv, move(cb));
+  io_mgr_.WriteAsync(req->file_offset, sv, move(cb));
   ++stats_.external_writes;
 
 #else
@@ -104,9 +105,18 @@ void TieredStorage::FinishIoRequest(int io_res, ActiveIoRequest* req) {
 
     it->second.SetIoPending(false);
     if (success) {
+      auto* stats = db_slice_.MutableStats(ikey.db_indx);
+
+      size_t heap_size = it->second.MallocUsed();
       size_t item_size = it->second.Size();
+
+      stats->obj_memory_usage -= heap_size;
+      stats->strval_memory_usage -= heap_size;
+
       it->second.SetExternal(k_v.second, item_size);
-      ++db_slice_.MutableStats(ikey.db_indx)->external_entries;
+
+      stats->external_entries += 1;
+      stats->external_size += item_size;
     }
   }
   delete req;
@@ -118,7 +128,7 @@ void TieredStorage::FinishIoRequest(int io_res, ActiveIoRequest* req) {
   VLOG_IF(1, num_active_requests_ == 0) << "Finished active requests";
 }
 
-TieredStorage::TieredStorage(DbSlice* db_slice) : db_slice_(*db_slice) {
+TieredStorage::TieredStorage(DbSlice* db_slice) : db_slice_(*db_slice), pending_req_(256) {
 }
 
 TieredStorage::~TieredStorage() {
@@ -129,8 +139,9 @@ TieredStorage::~TieredStorage() {
 error_code TieredStorage::Open(const string& path) {
   error_code ec = io_mgr_.Open(path);
   if (!ec) {
-    if (io_mgr_.Size()) {  // Add initial storage.
-      alloc_.AddStorage(0, io_mgr_.Size());
+    if (io_mgr_.Span()) {  // Add initial storage.
+      alloc_.AddStorage(0, io_mgr_.Span());
+      stats_.storage_capacity = io_mgr_.Span();
     }
   }
   return ec;
@@ -146,6 +157,13 @@ void TieredStorage::Shutdown() {
   io_mgr_.Shutdown();
 }
 
+bool TieredStorage::ShouldFlush() {
+  if (num_active_requests_ >= FLAGS_tiered_storage_max_pending_writes)
+    return false;
+
+  return pending_req_.size() > pending_req_.capacity() / 2;
+}
+
 error_code TieredStorage::UnloadItem(DbIndex db_index, PrimeIterator it) {
   CHECK_EQ(OBJ_STRING, it->second.ObjType());
 
@@ -153,148 +171,146 @@ error_code TieredStorage::UnloadItem(DbIndex db_index, PrimeIterator it) {
   error_code ec;
 
   pending_unload_bytes_ += blob_len;
-  if (db_index >= db_arr_.size()) {
+  /*if (db_index >= db_arr_.size()) {
     db_arr_.resize(db_index + 1);
   }
 
   if (db_arr_[db_index] == nullptr) {
     db_arr_[db_index] = new PerDb;
+  }*/
+
+  // PerDb* db = db_arr_[db_index];
+  pending_req_.EmplaceOrOverride(PendingReq{it.bucket_cursor().value(), db_index});
+  // db->pending_upload[it.bucket_cursor().value()] += blob_len;
+
+  // size_t grow_size = 0;
+
+  if (ShouldFlush()) {
+    FlushPending();
   }
 
-  PerDb* db = db_arr_[db_index];
-  db->pending_upload[it.bucket_cursor().value()] += blob_len;
-
-  size_t grow_size = 0;
-  if (!io_mgr_.grow_pending() && pending_unload_bytes_ >= ExternalAllocator::kMinBlockSize) {
-    grow_size = SerializePendingItems();
-  }
-
-  if (grow_size == 0 && alloc_.allocated_bytes() > size_t(alloc_.capacity() * 0.85)) {
-    grow_size = 1ULL << 28;
-  }
-
-  if (grow_size && !io_mgr_.grow_pending()) {
-    size_t start = io_mgr_.Size();
-
-    auto cb = [start, grow_size, this](int io_res) {
-      if (io_res == 0) {
-        alloc_.AddStorage(start, grow_size);
-        stats_.storage_capacity += grow_size;
-      } else {
-        LOG_FIRST_N(ERROR, 10) << "Error enlarging storage " << io_res;
-      }
-    };
-
-    ec = io_mgr_.GrowAsync(grow_size, move(cb));
+  // if we reached high utilization of the file range - try to grow the file.
+  if (alloc_.allocated_bytes() > size_t(alloc_.capacity() * 0.85)) {
+    InitiateGrow(1ULL << 28);
   }
 
   return ec;
 }
 
-size_t TieredStorage::SerializePendingItems() {
-  DCHECK(!io_mgr_.grow_pending());
+bool IsObjFitToUnload(const PrimeValue& pv) {
+  return pv.ObjType() == OBJ_STRING && !pv.IsExternal() && pv.Size() >= 64 && !pv.HasIoPending();
+};
 
-  vector<pair<size_t, uint64_t>> sorted_cursors;
-  constexpr size_t kArrLen = 64;
+void TieredStorage::FlushPending() {
+  DCHECK(!io_mgr_.grow_pending() && !pending_req_.empty());
 
-  PrimeTable::iterator iters[kArrLen];
-  unsigned iter_count = 0;
-  bool break_early = false;
+  vector<pair<DbIndex, uint64_t>> canonic_req;
+  canonic_req.reserve(pending_req_.size());
 
-  auto is_good = [](const PrimeValue& pv) {
-    return pv.ObjType() == OBJ_STRING && !pv.IsExternal() && pv.Size() >= 64 && !pv.HasIoPending();
-  };
-
-  auto tr_cb = [&](PrimeTable::iterator it) {
-    if (is_good(it->second)) {
-      CHECK_LT(iter_count, kArrLen);
-      iters[iter_count++] = it;
-    }
-  };
-
-  size_t open_block_size = 0;
-  size_t file_offset = 0;
-  size_t block_offset = 0;
-  ActiveIoRequest* active_req = nullptr;
-
-  for (size_t i = 0; i < db_arr_.size(); ++i) {
-    PerDb* db = db_arr_[i];
-    if (db == nullptr || db->pending_upload.empty())
-      continue;
-
-    sorted_cursors.resize(db->pending_upload.size());
-    size_t index = 0;
-    for (const auto& k_v : db->pending_upload) {
-      sorted_cursors[index++] = {k_v.second, k_v.first};
-    }
-    sort(sorted_cursors.begin(), sorted_cursors.end(), std::greater<>());
-    DbIndex db_ind = i;
-
-    for (const auto& pair : sorted_cursors) {
-      uint64_t cursor_val = pair.second;
-      PrimeTable::cursor curs(cursor_val);
-      db_slice_.GetTables(db_ind).first->Traverse(curs, tr_cb);
-
-      for (unsigned j = 0; j < iter_count; ++j) {
-        PrimeIterator it = iters[j];
-        size_t item_size = it->second.Size();
-        DCHECK_GT(item_size, 0u);
-
-        if (item_size + block_offset > open_block_size) {
-          if (open_block_size > 0) {  // need to close
-            // save the block asynchronously.
-            ++submitted_io_writes_;
-            submitted_io_write_size_ += open_block_size;
-
-            SendIoRequest(file_offset, open_block_size, active_req);
-            open_block_size = 0;
-          }
-
-          if (pending_unload_bytes_ < unsigned(0.8 * ExternalAllocator::kMinBlockSize)) {
-            break_early = true;
-            break;
-          }
-
-          DCHECK_EQ(0u, open_block_size);
-          int64_t res = alloc_.Malloc(item_size);
-          if (res < 0) {
-            return -res;
-          }
-
-          file_offset = res;
-          open_block_size = ExternalAllocator::GoodSize(item_size);
-          block_offset = 0;
-          ++num_active_requests_;
-          active_req = new ActiveIoRequest(open_block_size);
-        }
-
-        DCHECK_LE(item_size + block_offset, open_block_size);
-
-        it->second.GetString(active_req->block_ptr + block_offset);
-
-        DCHECK(!it->second.HasIoPending());
-        it->second.SetIoPending(true);
-
-        IndexKey key(db_ind, it->first.AsRef());
-        bool added = active_req->entries.emplace(move(key), file_offset + block_offset).second;
-        CHECK(added);
-        block_offset += item_size;  // saved into opened block.
-        pending_unload_bytes_ -= item_size;
-      }
-      iter_count = 0;
-      db->pending_upload.erase(cursor_val);
-    }  // sorted_cursors
-
-    if (break_early)
-      break;
-    DCHECK(db->pending_upload.empty());
-  }  // db_arr
-
-  if (open_block_size > 0) {
-    SendIoRequest(file_offset, open_block_size, active_req);
+  for (size_t i = 0; i < pending_req_.size(); ++i) {
+    const PendingReq* req = pending_req_.GetItem(i);
+    canonic_req.emplace_back(req->db_indx, req->cursor);
+  }
+  pending_req_.ConsumeHead(pending_req_.size());
+  // remove duplicates and sort.
+  {
+    sort(canonic_req.begin(), canonic_req.end());
+    auto it = unique(canonic_req.begin(), canonic_req.end());
+    canonic_req.resize(it - canonic_req.begin());
   }
 
-  return 0;
+  // TODO: we could add item size and sort from largest to smallest before
+  // the aggregation.
+  constexpr size_t kMaxBatchLen = 64;
+  PrimeTable::iterator single_batch[kMaxBatchLen];
+  unsigned batch_len = 0;
+
+  auto tr_cb = [&](PrimeTable::iterator it) {
+    if (IsObjFitToUnload(it->second)) {
+      CHECK_LT(batch_len, kMaxBatchLen);
+      single_batch[batch_len++] = it;
+    }
+  };
+
+  size_t active_batch_size = 0;
+  size_t batch_offset = 0;
+  ActiveIoRequest* active_req = nullptr;
+
+  for (size_t i = 0; i < canonic_req.size(); ++i) {
+    DbIndex db_ind = canonic_req[i].first;
+    uint64_t cursor_val = canonic_req[i].second;
+    PrimeTable::cursor curs(cursor_val);
+    db_slice_.GetTables(db_ind).first->Traverse(curs, tr_cb);
+
+    for (unsigned j = 0; j < batch_len; ++j) {
+      PrimeIterator it = single_batch[j];
+      size_t item_size = it->second.Size();
+      DCHECK_GT(item_size, 0u);
+
+      if (item_size + batch_offset > active_batch_size) {
+        if (active_batch_size > 0) {  // need to close
+          // save the block asynchronously.
+          ++submitted_io_writes_;
+          submitted_io_write_size_ += active_batch_size;
+
+          SendIoRequest(active_batch_size, active_req);
+          active_batch_size = 0;
+        }
+
+        DCHECK_EQ(0u, active_batch_size);
+        int64_t res = alloc_.Malloc(item_size);
+        if (res < 0) {
+          InitiateGrow(-res);
+          return;
+        }
+
+        active_batch_size = ExternalAllocator::GoodSize(item_size);
+        active_req = new ActiveIoRequest(res, active_batch_size);
+        stats_.storage_reserved += active_batch_size;
+
+        batch_offset = 0;
+        ++num_active_requests_;
+      }
+
+      DCHECK_LE(item_size + batch_offset, active_batch_size);
+
+      it->second.GetString(active_req->block_ptr + batch_offset);
+
+      DCHECK(!it->second.HasIoPending());
+      it->second.SetIoPending(true);
+
+      IndexKey key(db_ind, it->first.AsRef());
+      bool added =
+          active_req->entries.emplace(move(key), active_req->file_offset + batch_offset).second;
+      CHECK(added);
+      batch_offset += item_size;  // saved into opened block.
+    }
+    batch_len = 0;
+  }
+
+  if (active_batch_size > 0) {
+    SendIoRequest(active_batch_size, active_req);
+  }
+}
+
+void TieredStorage::InitiateGrow(size_t grow_size) {
+  if (io_mgr_.grow_pending())
+    return;
+  DCHECK_GT(grow_size, 0u);
+
+  size_t start = io_mgr_.Span();
+
+  auto cb = [start, grow_size, this](int io_res) {
+    if (io_res == 0) {
+      alloc_.AddStorage(start, grow_size);
+      stats_.storage_capacity += grow_size;
+    } else {
+      LOG_FIRST_N(ERROR, 10) << "Error enlarging storage " << io_res;
+    }
+  };
+
+  error_code ec = io_mgr_.GrowAsync(grow_size, move(cb));
+  CHECK(!ec) << "TBD";  // TODO
 }
 
 }  // namespace dfly
diff --git a/src/server/tiered_storage.h b/src/server/tiered_storage.h
index b24e48f..3357772 100644
--- a/src/server/tiered_storage.h
+++ b/src/server/tiered_storage.h
@@ -5,6 +5,8 @@
 
 #include <absl/container/flat_hash_map.h>
 
+#include "base/ring_buffer.h"
+
 #include "core/external_alloc.h"
 #include "server/common.h"
 #include "server/io_mgr.h"
@@ -36,10 +38,11 @@ class TieredStorage {
  private:
   struct ActiveIoRequest;
 
-  // return 0 if everything was sent.
-  // if more storage is needed returns requested size in bytes.
-  size_t SerializePendingItems();
-  void SendIoRequest(size_t offset, size_t req_size, ActiveIoRequest* req);
+  bool ShouldFlush();
+
+  void FlushPending();
+  void InitiateGrow(size_t size);
+  void SendIoRequest(size_t req_size, ActiveIoRequest* req);
   void FinishIoRequest(int io_res, ActiveIoRequest* req);
 
   DbSlice& db_slice_;
@@ -59,12 +62,21 @@ class TieredStorage {
   };
 
   struct PerDb {
-    // map of cursor -> pending size
-    absl::flat_hash_map<uint64_t, size_t> pending_upload;
     absl::flat_hash_map<PrimeKey, ActiveIoRequest*, Hasher> active_requests;
   };
 
   std::vector<PerDb*> db_arr_;
+
+  struct PendingReq {
+    uint64_t cursor;
+    DbIndex db_indx = kInvalidDbId;
+  };
+
+  base::RingBuffer<PendingReq> pending_req_;
+
+  // map of cursor -> pending size
+  // absl::flat_hash_map<uint64_t, size_t> pending_upload;
+
   TieredStats stats_;
 };
 
diff --git a/tools/docker/Dockerfile.ubuntu-prod b/tools/docker/Dockerfile.ubuntu-prod
index b2d07ca..d4fddfe 100644
--- a/tools/docker/Dockerfile.ubuntu-prod
+++ b/tools/docker/Dockerfile.ubuntu-prod
@@ -6,7 +6,7 @@ COPY src/  ./src/
 COPY helio/  ./helio/
 COPY patches/  ./patches/
 COPY CMakeLists.txt ./
-RUN ./helio/blaze.sh -release
+RUN ./helio/blaze.sh -release -DBoost_USE_STATIC_LIBS=ON
 
 WORKDIR build-opt
 RUN ninja dragonfly