block.state.commit is slow

I found that `block.state.commit` function is slow.
In Corgi network, when a block has a transaction that splits one UTXO to 100 UTXOs, the `block.state.commit` function takes 7 seconds when called by a proposer, takes 5 seconds when is called by other validators.

I added logs to find the function. You can see the logs in this [link](https://github.com/CodeChain-io/codechain/pull/1718)

Here are the sample logs.

```
// in proposer
#105317671 2019-07-25 10:51:27 UTC Client Worker CodeChain-io/codechain#2 TRACE miner Adding transaction 0x7a2813b09fc75f31e94f10af6f8e80d4fdf9e7ab3a856852a5c76a75b5b62018 took 13.64375ms
#105317671 2019-07-25 10:51:27 UTC Client Worker CodeChain-io/codechain#2 DEBUG miner Pushed 1/1 transactions
#105317671 2019-07-25 10:51:27 UTC Client Worker CodeChain-io/codechain#2 DEBUG miner Get parent hash
#105317671 2019-07-25 10:51:27 UTC Client Worker CodeChain-io/codechain#2 DEBUG miner Get parent header
#105317671 2019-07-25 10:51:27 UTC Client Worker CodeChain-io/codechain#2 DEBUG miner Get parent view
#105317671 2019-07-25 10:51:27 UTC Client Worker CodeChain-io/codechain#2 DEBUG miner Get transactions root
#105317671 2019-07-25 10:51:27 UTC Client Worker CodeChain-io/codechain#2 DEBUG miner Clone block state
#105317671 2019-07-25 10:51:27 UTC Client Worker CodeChain-io/codechain#2 DEBUG miner Call on_close_block
#105317671 2019-07-25 10:51:27 UTC Client Worker CodeChain-io/codechain#2 TRACE state add_balance(0x6850…65e1, 50): 2639520825
#105317671 2019-07-25 10:51:27 UTC Client Worker CodeChain-io/codechain#2 TRACE state add_balance(0x6202…8750, 19): 1300650642
#105317671 2019-07-25 10:51:27 UTC Client Worker CodeChain-io/codechain#2 TRACE state add_balance(0x263b…fcb1, 30): 1762899421
#105317671 2019-07-25 10:51:27 UTC Client Worker CodeChain-io/codechain#2 TRACE state add_balance(0x0968…b3f6, 1): 919023814
#105317671 2019-07-25 10:51:27 UTC Client Worker CodeChain-io/codechain#2 DEBUG miner commit state

#105317671 2019-07-25 10:51:34 UTC Client Worker CodeChain-io/codechain#2 DEBUG miner Set transactions root
#105317671 2019-07-25 10:51:34 UTC Client Worker CodeChain-io/codechain#2 DEBUG miner set state root
#105317671 2019-07-25 10:51:34 UTC event.loop INFO rpc RPC call(slog([]))
#105317671 2019-07-25 10:51:34 UTC Client Worker CodeChain-io/codechain#2 DEBUG miner Close block
#105317671 2019-07-25 10:51:34 UTC Client Worker CodeChain-io/codechain#2 DEBUG miner Before get write access of mem_pool
#105317671 2019-07-25 10:51:34 UTC Client Worker CodeChain-io/codechain#2 DEBUG miner After get write access of mem_pool
#105317671 2019-07-25 10:51:34 UTC Client Worker CodeChain-io/codechain#2 TRACE mem_pool remove() called, time: 2126657, timestamp: 1564051884
#105317671 2019-07-25 10:51:34 UTC Client Worker CodeChain-io/codechain#2 TRACE miner update_sealing: engine indicates internal sealing
#105317671 2019-07-25 10:51:34 UTC Client Worker CodeChain-io/codechain#2 TRACE miner seal_block_internally: attempting internal seal.
#105317671 2019-07-25 10:51:34 UTC tendermint TRACE engine Proposer nonce: 26
```

```
// in another validator
#608329186 2019-07-25 11:17:25 UTC Blocks Verifier CodeChain-io/codechain#1 DEBUG miner Before lock block 2126978

#608329186 2019-07-25 11:17:30 UTC Blocks Verifier CodeChain-io/codechain#1 DEBUG miner After lock block 2126978
```

Bắt đầu với lời gọi block.state.commit được xác định trong các log và kiểm tra các đường đi của proposer và validator được mô tả trong issue. Profile trường hợp 100-UTXO dựa trên các timing log được cung cấp; được xem là hoàn tất khi xác định được nút thắt cổ chai của commit và giảm được các độ trễ đã báo cáo.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.