Consider reusing active buffer.

9 files changed, 138 insertions, 37 deletions

diff --git a/vespalib/src/tests/datastore/array_store/array_store_test.cpp b/vespalib/src/tests/datastore/array_store/array_store_test.cpp
index 417d8b80d87..562ecaaecfa 100644
--- a/vespalib/src/tests/datastore/array_store/array_store_test.cpp
+++ b/vespalib/src/tests/datastore/array_store/array_store_test.cpp
@@ -150,13 +150,13 @@ TEST("require that we test with trivial and non-trivial types")
 
 TEST_F("control static sizes", NumberFixture(3)) {
 #ifdef _LIBCPP_VERSION
-    EXPECT_EQUAL(400u, sizeof(f.store));
+    EXPECT_EQUAL(424u, sizeof(f.store));
     EXPECT_EQUAL(296u, sizeof(NumberFixture::ArrayStoreType::DataStoreType));
 #else
-    EXPECT_EQUAL(432u, sizeof(f.store));
+    EXPECT_EQUAL(456u, sizeof(f.store));
     EXPECT_EQUAL(328u, sizeof(NumberFixture::ArrayStoreType::DataStoreType));
 #endif
-    EXPECT_EQUAL(72u, sizeof(NumberFixture::ArrayStoreType::SmallArrayType));
+    EXPECT_EQUAL(96u, sizeof(NumberFixture::ArrayStoreType::SmallArrayType));
     MemoryUsage usage = f.store.getMemoryUsage();
     EXPECT_EQUAL(960u, usage.allocatedBytes());
     EXPECT_EQUAL(32u, usage.usedBytes());
diff --git a/vespalib/src/tests/datastore/buffer_type/buffer_type_test.cpp b/vespalib/src/tests/datastore/buffer_type/buffer_type_test.cpp
index 414c35864ac..4cd192f602f 100644
--- a/vespalib/src/tests/datastore/buffer_type/buffer_type_test.cpp
+++ b/vespalib/src/tests/datastore/buffer_type/buffer_type_test.cpp
@@ -49,7 +49,7 @@ struct Fixture {
     }
     ~Fixture() {
         for (auto& setup : setups) {
-            bufferType.onHold(&setup._usedElems, &setup._deadElems);
+            bufferType.onHold(setup._bufferId, &setup._usedElems, &setup._deadElems);
             bufferType.onFree(setup._usedElems);
         }
     }
@@ -134,9 +134,9 @@ TEST("arrays to alloc considers used elements across all active buffers of same
 {
     Fixture f(Setup().used(6 * 4));
     f.assertArraysToAlloc(6 * 0.5);
-    f.add_setup(Setup().used(8 * 4));
+    f.add_setup(Setup().used(8 * 4).bufferId(2));
     f.assertArraysToAlloc((6 + 8) * 0.5);
-    f.add_setup(Setup().used(10 * 4));
+    f.add_setup(Setup().used(10 * 4).bufferId(3));
     f.assertArraysToAlloc((6 + 8 + 10) * 0.5);
 }
 
@@ -144,7 +144,7 @@ TEST("arrays to alloc considers used elements across all active buffers of same
 {
     Fixture f(Setup().used(6 * 4));
     f.assertArraysToAlloc(6 * 0.5);
-    f.add_setup(Setup().used(8 * 4).resizing(true));
+    f.add_setup(Setup().used(8 * 4).resizing(true).bufferId(2));
     f.assertArraysToAlloc(8 + (6 + 8) * 0.5);
 }
 
@@ -152,9 +152,9 @@ TEST("arrays to alloc considers (and subtracts) dead elements across all active
 {
     Fixture f(Setup().used(6 * 4).dead(2 * 4));
     f.assertArraysToAlloc((6 - 2) * 0.5);
-    f.add_setup(Setup().used(12 * 4).dead(4 * 4));
+    f.add_setup(Setup().used(12 * 4).dead(4 * 4).bufferId(2));
     f.assertArraysToAlloc((6 - 2 + 12 - 4) * 0.5);
-    f.add_setup(Setup().used(20 * 4).dead(6 * 4));
+    f.add_setup(Setup().used(20 * 4).dead(6 * 4).bufferId(3));
     f.assertArraysToAlloc((6 - 2 + 12 - 4 + 20 - 6) * 0.5);
 }
 
@@ -162,7 +162,7 @@ TEST("arrays to alloc considers (and subtracts) dead elements across all active
 {
     Fixture f(Setup().used(6 * 4).dead(2 * 4));
     f.assertArraysToAlloc((6 - 2) * 0.5);
-    f.add_setup(Setup().used(12 * 4).dead(4 * 4).resizing(true));
+    f.add_setup(Setup().used(12 * 4).dead(4 * 4).resizing(true).bufferId(2));
     f.assertArraysToAlloc(12 + (6 - 2 + 12 - 4) * 0.5);
 }
 
diff --git a/vespalib/src/tests/datastore/datastore/datastore_test.cpp b/vespalib/src/tests/datastore/datastore/datastore_test.cpp
index 548ab9199da..1c4817ea35f 100644
--- a/vespalib/src/tests/datastore/datastore/datastore_test.cpp
+++ b/vespalib/src/tests/datastore/datastore/datastore_test.cpp
@@ -55,6 +55,7 @@ public:
 
 
 using GrowthStats = std::vector<int>;
+using BufferStats = std::vector<int>;
 
 constexpr float ALLOC_GROW_FACTOR = 0.4;
 constexpr size_t HUGE_PAGE_ARRAY_SIZE = (MemoryAllocator::HUGEPAGE_SIZE / sizeof(int));
@@ -123,6 +124,19 @@ public:
             ++i;
         }
     }
+    BufferStats getBuffers(size_t bufs) {
+        BufferStats buffers;
+        while (buffers.size() < bufs) {
+            RefType iRef = (_type.getArraySize() == 1) ?
+                           (_store.template allocator<DataType>(_typeId).alloc().ref) :
+                           (_store.template allocator<DataType>(_typeId).allocArray(_type.getArraySize()).ref);
+            int buffer_id = iRef.bufferId();
+            if (buffers.empty() || buffers.back() != buffer_id) {
+                buffers.push_back(buffer_id);
+            }
+        }
+        return buffers;
+    }
     vespalib::MemoryUsage getMemoryUsage() const { return _store.getMemoryUsage(); }
 };
 
@@ -563,7 +577,7 @@ TEST(DataStoreTest, require_that_buffer_growth_works)
     assertGrowStats({ 4, 4, 4, 4, 8, 16, 16, 32, 64, 64 },
                     { 4 }, 20, 4, 0);
     // Resize if buffer size is less than 4, min size 0
-    assertGrowStats({ 4, 4, 8, 32, 32, 32, 64, 128, 128, 128 },
+    assertGrowStats({ 4, 4, 8, 32, 32, 64, 64, 128, 128, 128 },
                     { 0, 1, 2, 4 }, 4, 0, 4);
     // Always switch to new buffer, min size 16
     assertGrowStats({ 16, 16, 16, 32, 32, 64, 128, 128, 128 },
@@ -580,7 +594,7 @@ TEST(DataStoreTest, require_that_buffer_growth_works)
 
     // Buffers with sizes larger than the huge page size of the mmap allocator.
     ASSERT_EQ(524288u, HUGE_PAGE_ARRAY_SIZE);
-    assertGrowStats({ 262144, 524288, 524288, 524288 * 3, 524288 * 3, 524288 * 4, 524288 * 5, 524288 * 5, 524288 * 5, 524288 * 5 },
+    assertGrowStats({ 262144, 524288, 524288, 524288 * 3, 524288 * 3, 524288 * 5, 524288 * 5, 524288 * 5, 524288 * 5, 524288 * 5 },
                     { 0, 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384, 32768, 65536, 131072, 262144 },
                     4, 0, HUGE_PAGE_ARRAY_SIZE / 2, HUGE_PAGE_ARRAY_SIZE * 5);
 }
@@ -615,10 +629,10 @@ TEST(DataStoreTest, require_that_offset_in_EntryRefT_is_within_bounds_when_alloc
      *      The max bytes to alloc is: maxArrays * arraySize * elementSize.
      */
     assertGrowStats<uint8_t>({8192,16384,16384,65536,65536,98304,98304,98304,98304,98304,98304,98304}, 3);
-    assertGrowStats<uint8_t>({16384,16384,65536,65536,65536,131072,163840,163840,163840,163840,163840,163840}, 5);
+    assertGrowStats<uint8_t>({16384,16384,65536,65536,131072,131072,163840,163840,163840,163840,163840,163840}, 5);
     assertGrowStats<uint8_t>({16384,32768,32768,131072,131072,229376,229376,229376,229376,229376,229376,229376}, 7);
     assertGrowStats<uint32_t>({8192,16384,16384,65536,65536,98304,98304,98304,98304,98304,98304,98304}, 3);
-    assertGrowStats<uint32_t>({16384,16384,65536,65536,65536,131072,163840,163840,163840,163840,163840,163840}, 5);
+    assertGrowStats<uint32_t>({16384,16384,65536,65536,131072,131072,163840,163840,163840,163840,163840,163840}, 5);
     assertGrowStats<uint32_t>({16384,32768,32768,131072,131072,229376,229376,229376,229376,229376,229376,229376}, 7);
 }
 
@@ -666,8 +680,24 @@ TEST(DataStoreTest, can_set_memory_allocator)
     EXPECT_EQ(AllocStats(3, 3), stats);
 }
 
+namespace {
+
+void
+assertBuffers(BufferStats exp_buffers, size_t num_arrays_for_new_buffer)
+{
+    EXPECT_EQ(exp_buffers, IntGrowStore(1, 1, 1024, num_arrays_for_new_buffer).getBuffers(exp_buffers.size()));
+}
+
+}
+
+TEST(DataStoreTest, can_reuse_active_buffer_as_primary_buffer)
+{
+    assertBuffers({ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11}, 0);
+    assertBuffers({ 1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3}, 16);
+}
+
 TEST(DataStoreTest, control_static_sizes) {
-    EXPECT_EQ(72, sizeof(BufferTypeBase));
+    EXPECT_EQ(96, sizeof(BufferTypeBase));
     EXPECT_EQ(32, sizeof(BufferState::FreeList));
     EXPECT_EQ(1, sizeof(BufferState::State));
     EXPECT_EQ(144, sizeof(BufferState));
diff --git a/vespalib/src/vespa/vespalib/datastore/buffer_type.cpp b/vespalib/src/vespa/vespalib/datastore/buffer_type.cpp
index eb5865cd68c..068c58a163c 100644
--- a/vespalib/src/vespa/vespalib/datastore/buffer_type.cpp
+++ b/vespalib/src/vespa/vespalib/datastore/buffer_type.cpp
@@ -32,10 +32,10 @@ BufferTypeBase::BufferTypeBase(uint32_t arraySize,
       _maxArrays(maxArrays),
       _numArraysForNewBuffer(std::min(numArraysForNewBuffer, maxArrays)),
       _allocGrowFactor(allocGrowFactor),
-      _activeBuffers(0),
       _holdBuffers(0),
       _holdUsedElems(0),
-      _aggr_counts()
+      _aggr_counts(),
+      _active_buffers()
 {
 }
 
@@ -48,10 +48,10 @@ BufferTypeBase::BufferTypeBase(uint32_t arraySize,
 
 BufferTypeBase::~BufferTypeBase()
 {
-    assert(_activeBuffers == 0);
     assert(_holdBuffers == 0);
     assert(_holdUsedElems == 0);
     assert(_aggr_counts.empty());
+    assert(_active_buffers.empty());
 }
 
 ElemCount
@@ -63,8 +63,9 @@ BufferTypeBase::getReservedElements(uint32_t bufferId) const
 void
 BufferTypeBase::onActive(uint32_t bufferId, ElemCount* usedElems, ElemCount* deadElems, void* buffer)
 {
-    ++_activeBuffers;
     _aggr_counts.add_buffer(usedElems, deadElems);
+    assert(std::find(_active_buffers.begin(), _active_buffers.end(), bufferId) == _active_buffers.end());
+    _active_buffers.emplace_back(bufferId);
     size_t reservedElems = getReservedElements(bufferId);
     if (reservedElems != 0u) {
         initializeReservedElements(buffer, reservedElems);
@@ -74,10 +75,12 @@ BufferTypeBase::onActive(uint32_t bufferId, ElemCount* usedElems, ElemCount* dea
 }
 
 void
-BufferTypeBase::onHold(const ElemCount* usedElems, const ElemCount* deadElems)
+BufferTypeBase::onHold(uint32_t buffer_id, const ElemCount* usedElems, const ElemCount* deadElems)
 {
-    --_activeBuffers;
     ++_holdBuffers;
+    auto itr = std::find(_active_buffers.begin(), _active_buffers.end(), buffer_id);
+    assert(itr != _active_buffers.end());
+    _active_buffers.erase(itr);
     _aggr_counts.remove_buffer(usedElems, deadElems);
     _holdUsedElems += *usedElems;
 }
@@ -90,6 +93,17 @@ BufferTypeBase::onFree(ElemCount usedElems)
     _holdUsedElems -= usedElems;
 }
 
+void
+BufferTypeBase::resume_primary_buffer(uint32_t buffer_id, ElemCount* used_elems, ElemCount* dead_elems)
+{
+    auto itr = std::find(_active_buffers.begin(), _active_buffers.end(), buffer_id);
+    assert(itr != _active_buffers.end());
+    _active_buffers.erase(itr);
+    _active_buffers.emplace_back(buffer_id);
+    _aggr_counts.remove_buffer(used_elems, dead_elems);
+    _aggr_counts.add_buffer(used_elems, dead_elems);
+}
+
 const alloc::MemoryAllocator*
 BufferTypeBase::get_memory_allocator() const
 {
@@ -141,10 +155,11 @@ BufferTypeBase::calcArraysToAlloc(uint32_t bufferId, ElemCount elemsNeeded, bool
 uint32_t
 BufferTypeBase::get_scaled_num_arrays_for_new_buffer() const
 {
-    if (_activeBuffers <= 1u || _numArraysForNewBuffer == 0u) {
+    uint32_t active_buffers_count = get_active_buffers_count();
+    if (active_buffers_count <= 1u || _numArraysForNewBuffer == 0u) {
         return _numArraysForNewBuffer;
     }
-    double scale_factor = std::pow(1.0 + _allocGrowFactor, _activeBuffers - 1);
+    double scale_factor = std::pow(1.0 + _allocGrowFactor, active_buffers_count - 1);
     double scaled_result = _numArraysForNewBuffer * scale_factor;
     if (scaled_result >= _maxArrays) {
         return _maxArrays;
diff --git a/vespalib/src/vespa/vespalib/datastore/buffer_type.h b/vespalib/src/vespa/vespalib/datastore/buffer_type.h
index 1f024743c8b..62d9282aae0 100644
--- a/vespalib/src/vespa/vespalib/datastore/buffer_type.h
+++ b/vespalib/src/vespa/vespalib/datastore/buffer_type.h
@@ -61,8 +61,9 @@ public:
     virtual void cleanHold(void *buffer, size_t offset, ElemCount numElems, CleanContext cleanCtx) = 0;
     size_t getArraySize() const { return _arraySize; }
     virtual void onActive(uint32_t bufferId, ElemCount* usedElems, ElemCount* deadElems, void* buffer);
-    void onHold(const ElemCount* usedElems, const ElemCount* deadElems);
+    void onHold(uint32_t buffer_id, const ElemCount* usedElems, const ElemCount* deadElems);
     virtual void onFree(ElemCount usedElems);
+    void resume_primary_buffer(uint32_t buffer_id, ElemCount* used_elems, ElemCount* dead_elems);
     virtual const alloc::MemoryAllocator* get_memory_allocator() const;
 
     /**
@@ -72,9 +73,11 @@ public:
 
     void clampMaxArrays(uint32_t maxArrays);
 
-    uint32_t getActiveBuffers() const { return _activeBuffers; }
+    uint32_t get_active_buffers_count() const { return _active_buffers.size(); }
+    const std::vector<uint32_t>& get_active_buffers() const noexcept { return _active_buffers; }
     size_t getMaxArrays() const { return _maxArrays; }
     uint32_t get_scaled_num_arrays_for_new_buffer() const;
+    uint32_t get_num_arrays_for_new_buffer() const noexcept { return _numArraysForNewBuffer; }
 protected:
 
     struct BufferCounts {
@@ -120,6 +123,7 @@ protected:
     uint32_t _holdBuffers;
     size_t   _holdUsedElems;  // Number of used elements in all held buffers for this type.
     AggregatedBufferCounts _aggr_counts;
+    std::vector<uint32_t>  _active_buffers;
 };
 
 /**
diff --git a/vespalib/src/vespa/vespalib/datastore/bufferstate.cpp b/vespalib/src/vespa/vespalib/datastore/bufferstate.cpp
index 68606c5ea19..704fabffe25 100644
--- a/vespalib/src/vespa/vespalib/datastore/bufferstate.cpp
+++ b/vespalib/src/vespa/vespalib/datastore/bufferstate.cpp
@@ -138,7 +138,7 @@ BufferState::onActive(uint32_t bufferId, uint32_t typeId,
 
 
 void
-BufferState::onHold()
+BufferState::onHold(uint32_t buffer_id)
 {
     assert(_state == ACTIVE);
     assert(_typeHandler != nullptr);
@@ -148,7 +148,7 @@ BufferState::onHold()
     assert(_holdElems <= (_usedElems - _deadElems));
     _deadElems = 0;
     _holdElems = _usedElems; // Put everyting on hold
-    _typeHandler->onHold(&_usedElems, &_deadElems);
+    _typeHandler->onHold(buffer_id, &_usedElems, &_deadElems);
     if ( ! isFreeListEmpty()) {
         removeFromFreeListList();
         FreeList().swap(_freeList);
@@ -191,7 +191,7 @@ BufferState::onFree(void *&buffer)
 
 
 void
-BufferState::dropBuffer(void *&buffer)
+BufferState::dropBuffer(uint32_t buffer_id, void *&buffer)
 {
     if (_state == FREE) {
         assert(buffer == nullptr);
@@ -199,7 +199,7 @@ BufferState::dropBuffer(void *&buffer)
     }
     assert(buffer != nullptr || _allocElems == 0);
     if (_state == ACTIVE) {
-        onHold();
+        onHold(buffer_id);
     }
     if (_state == HOLD) {
         onFree(buffer);
@@ -301,5 +301,11 @@ BufferState::fallbackResize(uint32_t bufferId,
     std::atomic_thread_fence(std::memory_order_release);
 }
 
+void
+BufferState::resume_primary_buffer(uint32_t buffer_id)
+{
+    _typeHandler->resume_primary_buffer(buffer_id, &_usedElems, &_deadElems);
+}
+
 }
 
diff --git a/vespalib/src/vespa/vespalib/datastore/bufferstate.h b/vespalib/src/vespa/vespalib/datastore/bufferstate.h
index f8738f17daa..e95bef6f459 100644
--- a/vespalib/src/vespa/vespalib/datastore/bufferstate.h
+++ b/vespalib/src/vespa/vespalib/datastore/bufferstate.h
@@ -99,7 +99,7 @@ public:
     /**
      * Transition from ACTIVE to HOLD state.
      */
-    void onHold();
+    void onHold(uint32_t buffer_id);
 
     /**
      * Transition from HOLD to FREE state.
@@ -157,7 +157,7 @@ public:
     void cleanHold(void *buffer, size_t offset, ElemCount numElems) {
         _typeHandler->cleanHold(buffer, offset, numElems, BufferTypeBase::CleanContext(_extraUsedBytes, _extraHoldBytes));
     }
-    void dropBuffer(void *&buffer);
+    void dropBuffer(uint32_t buffer_id, void *&buffer);
     uint32_t getTypeId() const { return _typeId; }
     uint32_t getArraySize() const { return _arraySize; }
     size_t getDeadElems() const { return _deadElems; }
@@ -192,6 +192,7 @@ public:
     FreeList &freeList() { return _freeList; }
     const FreeListList *freeListList() const { return _freeListList; }
     FreeListList *freeListList() { return _freeListList; }
+    void resume_primary_buffer(uint32_t buffer_id);
 
 };
 
diff --git a/vespalib/src/vespa/vespalib/datastore/datastorebase.cpp b/vespalib/src/vespa/vespalib/datastore/datastorebase.cpp
index aff26fc7b84..008ab0f0af9 100644
--- a/vespalib/src/vespa/vespalib/datastore/datastorebase.cpp
+++ b/vespalib/src/vespa/vespalib/datastore/datastorebase.cpp
@@ -120,6 +120,47 @@ DataStoreBase::switch_primary_buffer(uint32_t typeId, size_t elemsNeeded)
     _primary_buffer_ids[typeId] = buffer_id;
 }
 
+bool
+DataStoreBase::consider_grow_active_buffer(uint32_t type_id, size_t elems_needed)
+{
+    auto type_handler = _typeHandlers[type_id];
+    uint32_t buffer_id = _primary_buffer_ids[type_id];
+    uint32_t active_buffers_count = type_handler->get_active_buffers_count();
+    constexpr uint32_t min_active_buffers = 4u;
+    if (active_buffers_count < min_active_buffers) {
+        return false;
+    }
+    if (type_handler->get_num_arrays_for_new_buffer() == 0u) {
+        return false;
+    }
+    assert(!_states[buffer_id].getCompacting());
+    uint32_t min_buffer_id = buffer_id;
+    size_t min_used = _states[buffer_id].size();
+    uint32_t checked_active_buffers = 1u;
+    for (auto &alt_buffer_id : type_handler->get_active_buffers()) {
+        if (alt_buffer_id != buffer_id && !_states[alt_buffer_id].getCompacting()) {
+            ++checked_active_buffers;
+            if (_states[alt_buffer_id].size() < min_used) {
+                min_buffer_id = alt_buffer_id;
+                min_used = _states[alt_buffer_id].size();
+            }
+        }
+    }
+    if (checked_active_buffers < min_active_buffers) {
+        return false;
+    }
+    auto array_size = type_handler->getArraySize();
+    if (elems_needed + min_used > type_handler->getMaxArrays() * array_size) {
+        return false;
+    }
+    if (min_buffer_id != buffer_id) {
+        // Resume another active buffer for same type as primary buffer
+        _primary_buffer_ids[type_id] = min_buffer_id;
+        _states[min_buffer_id].resume_primary_buffer(min_buffer_id);
+    }
+    return true;
+}
+
 void
 DataStoreBase::switch_or_grow_primary_buffer(uint32_t typeId, size_t elemsNeeded)
 {
@@ -129,8 +170,11 @@ DataStoreBase::switch_or_grow_primary_buffer(uint32_t typeId, size_t elemsNeeded
     size_t numEntriesForNewBuffer = numArraysForNewBuffer * arraySize;
     uint32_t bufferId = _primary_buffer_ids[typeId];
     if (elemsNeeded + _states[bufferId].size() >= numEntriesForNewBuffer) {
-        // Don't try to resize existing buffer, new buffer will be large enough
-        switch_primary_buffer(typeId, elemsNeeded);
+        if (consider_grow_active_buffer(typeId, elemsNeeded)) {
+            fallbackResize(_primary_buffer_ids[typeId], elemsNeeded);
+        } else {
+            switch_primary_buffer(typeId, elemsNeeded);
+        }
     } else {
         fallbackResize(bufferId, elemsNeeded);
     }
@@ -214,7 +258,7 @@ DataStoreBase::dropBuffers()
 {
     uint32_t numBuffers = _buffers.size();
     for (uint32_t bufferId = 0; bufferId < numBuffers; ++bufferId) {
-        _states[bufferId].dropBuffer(_buffers[bufferId].getBuffer());
+        _states[bufferId].dropBuffer(bufferId, _buffers[bufferId].getBuffer());
     }
     _genHolder.clearHoldLists();
 }
@@ -234,7 +278,7 @@ DataStoreBase::getMemoryUsage() const
 void
 DataStoreBase::holdBuffer(uint32_t bufferId)
 {
-    _states[bufferId].onHold();
+    _states[bufferId].onHold(bufferId);
     size_t holdBytes = 0u;  // getMemStats() still accounts held buffers
     GenerationHeldBase::UP hold(new BufferHold(holdBytes, *this, bufferId));
     _genHolder.hold(std::move(hold));
@@ -429,8 +473,8 @@ DataStoreBase::startCompactWorstBuffer(uint32_t typeId)
 {
     uint32_t buffer_id = get_primary_buffer_id(typeId);
     const BufferTypeBase *typeHandler = _typeHandlers[typeId];
-    assert(typeHandler->getActiveBuffers() >= 1u);
-    if (typeHandler->getActiveBuffers() == 1u) {
+    assert(typeHandler->get_active_buffers_count() >= 1u);
+    if (typeHandler->get_active_buffers_count() == 1u) {
         // Single active buffer for type, no need for scan
         _states[buffer_id].setCompacting();
         _states[buffer_id].disableElemHoldList();
diff --git a/vespalib/src/vespa/vespalib/datastore/datastorebase.h b/vespalib/src/vespa/vespalib/datastore/datastorebase.h
index 5a50dba6a3c..97ead502408 100644
--- a/vespalib/src/vespa/vespalib/datastore/datastorebase.h
+++ b/vespalib/src/vespa/vespalib/datastore/datastorebase.h
@@ -232,6 +232,7 @@ public:
      */
     void switch_primary_buffer(uint32_t typeId, size_t elemsNeeded);
 
+    bool consider_grow_active_buffer(uint32_t type_id, size_t elems_needed);
     void switch_or_grow_primary_buffer(uint32_t typeId, size_t elemsNeeded);
 
     vespalib::MemoryUsage getMemoryUsage() const;