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  2. IMPALA-6425

Change Mempool memory allocation size to be <1MB to avoid allocating from CentralFreeList




      While tlipcon was investigating KRPC contention he noticed that MemPool::Allocate is doing 1MB allocations, which is somewhat of an anti-pattern with tcmalloc. 
      During the tests MemPool was doing several thousand 1MB allocs per second and those have to do a full scan of the tcmalloc span linked list, which is very slow and only gets slower
       1040384 bytes on the other hand is constant time. 
      It is not clear if a Power of 2 allocation size would help, worth experimenting with 512KB and 1040384 bytes. 

       /// The maximum size of chunk that should be allocated. Allocations larger than this
       /// size will get their own individual chunk.
       static const int MAX_CHUNK_SIZE = 8192*127


      #0  0x0000000002097407 in base::internal::SpinLockDelay(int volatile*, int, int) ()
      #1  0x00000000020e2049 in SpinLock::SlowLock() ()
      #2  0x0000000002124348 in tcmalloc::CentralFreeList::Populate() ()
      #3  0x0000000002124458 in tcmalloc::CentralFreeList::FetchFromOneSpansSafe(int, void**, void**) ()
      #4  0x00000000021244e8 in tcmalloc::CentralFreeList::RemoveRange(void**, void**, int) ()
      #5  0x0000000002131ee5 in tcmalloc::ThreadCache::FetchFromCentralCache(unsigned int, int, void* (*)(unsigned long)) ()
      #6  0x0000000000b2879a in impala::MemPool::FindChunk(long, bool) ()
      #7  0x0000000000b364f6 in impala::MemPool::Allocate(long) ()
      #8  0x0000000000b36674 in impala::FreePool::Allocate(long) ()
      #9  0x0000000000b353db in impala::RowBatch::Deserialize(kudu::Slice const&, kudu::Slice const&, long, bool, impala::FreePool*) ()
      #10 0x0000000000b35795 in impala::RowBatch::RowBatch(impala::RowDescriptor const*, impala::RowBatchHeaderPB const&, kudu::Slice const&, kudu::Slice const&, impala::FreePool*) ()
      #11 0x0000000000b1644f in impala::KrpcDataStreamRecvr::SenderQueue::AddBatchWork(long, impala::RowBatchHeaderPB const&, kudu::Slice const&, kudu::Slice const&, boost::unique_lock<impala::SpinLock>*) ()
      #12 0x0000000000b19135 in impala::KrpcDataStreamRecvr::SenderQueue::AddBatch(impala::TransmitDataRequestPB const*, kudu::rpc::RpcContext*) ()
      #13 0x0000000000b0ee30 in impala::KrpcDataStreamMgr::AddData(impala::TransmitDataRequestPB const*, kudu::rpc::RpcContext*) ()
      #14 0x0000000001187035 in kudu::rpc::GeneratedServiceIf::Handle(kudu::rpc::InboundCall*) ()
      #15 0x00000000011bc1cd in impala::ImpalaServicePool::RunThread(long) ()


      Also it appears that the thread above was a victim of thread below, yet allocations <1MB will make MemPool::Allocate content less over the CentralFreeList lock. 

      #0 0x0000003173ae5407 in madvise () from /lib64/libc.so.6
      #1 0x0000000002131cca in TCMalloc_SystemRelease(void*, unsigned long) ()
      #2 0x000000000212f26a in tcmalloc::PageHeap::DecommitSpan(tcmalloc::Span*) ()
      #3 0x000000000212f505 in tcmalloc::PageHeap::MergeIntoFreeList(tcmalloc::Span*) ()
      #4 0x000000000212f864 in tcmalloc::PageHeap::Delete(tcmalloc::Span*) ()
      #5 0x0000000002123cf7 in tcmalloc::CentralFreeList::ReleaseToSpans(void*) ()
      #6 0x0000000002123d9b in tcmalloc::CentralFreeList::ReleaseListToSpans(void*) ()
      #7 0x0000000002124067 in tcmalloc::CentralFreeList::InsertRange(void*, void*, int) ()
      #8 0x00000000021320a4 in tcmalloc::ThreadCache::ReleaseToCentralCache(tcmalloc::ThreadCache::FreeList*, unsigned int, int) ()
      #9 0x0000000002132575 in tcmalloc::ThreadCache::ListTooLong(tcmalloc::ThreadCache::FreeList*, unsigned int) ()
      #10 0x0000000000b276e0 in impala::MemPool::FreeAll() ()
      #11 0x0000000000b34655 in impala::RowBatch::Reset() ()
      #12 0x0000000000fe882f in impala::PartitionedAggregationNode::GetRowsStreaming(impala::RuntimeState*, impala::RowBatch*) ()
      #13 0x0000000000fe9771 in impala::PartitionedAggregationNode::GetNext(impala::RuntimeState*, impala::RowBatch*, bool*) ()
      #14 0x0000000000b78352 in impala::FragmentInstanceState::ExecInternal() ()
      #15 0x0000000000b7adc2 in impala::FragmentInstanceState::Exec() ()
      #16 0x0000000000b6a0da in impala::QueryState::ExecFInstance(impala::FragmentInstanceState*) ()




            tarmstrong Tim Armstrong
            mmokhtar Mostafa Mokhtar
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