The `getaddressesbylabel` API spends a lot more time than the `getaddressesbyaccount` API.

I generated addresses by the `getnewaddress` API, then, I measured time that the `getaddressesby*` API spends. It seems the algorithm of the `getaddressesbylabel` API takes **O(N ^ 2)** time! The results of my survey are as follows.

### getaddressesbylabel

bitcoind v0.17.1 on Ubuntu 16.04 (AWS EC2 t3.large)

#### 11,001 addresses

```sh
time sudo /usr/local/bin/bitcoin-cli -conf=/etc/bitcoin/bitcoin.conf getaddressesbylabel ""
# (omitted)
real    0m1.230s # 1.2s
user    0m0.044s
sys 0m0.048s
```

#### 111,001 addresses

```sh
time sudo /usr/local/bin/bitcoin-cli -conf=/etc/bitcoin/bitcoin.conf getaddressesbylabel ""
# (omitted)
real    1m37.027s # 97.0s
user    0m0.408s
sys 0m0.544s
```

#### 211,001 addresses

```sh
time sudo /usr/local/bin/bitcoin-cli -conf=/etc/bitcoin/bitcoin.conf getaddressesbylabel ""
# (omitted)
real    6m3.727s # 363.7s
user    0m0.800s
sys 0m0.900s
```

### getaddressesbyaccount

bitcoind v0.16.3 on Ubuntu 16.04 (AWS EC2 t3.large)

#### 11,001 addresses

```sh
time sudo /usr/local/bin/bitcoin-cli -conf=/etc/bitcoin/bitcoin.conf getaddressesbyaccount ""
# (omitted)
real    0m0.500s # 0.5s
user    0m0.092s
sys 0m0.160s
```

#### 111,001 addresses

```sh
time sudo /usr/local/bin/bitcoin-cli -conf=/etc/bitcoin/bitcoin.conf getaddressesbyaccount ""
# (omitted)
real    0m1.361s # 1.4s
user    0m0.168s
sys 0m0.348s
```

#### 211,001 addresses

```sh
time sudo /usr/local/bin/bitcoin-cli -conf=/etc/bitcoin/bitcoin.conf getaddressesbyaccount ""
# (omitted)
real    0m2.220s # 2.2s
user    0m0.384s
sys 0m0.532s
```

"  \"details\" : [\n"
            "    {\n"
            "      \"address\" : \"address\",          (string) The bitcoin address involved in the transaction\n"
            "      \"category\" :                      (string) The transaction category.\n"
            "                   \"send\"                  Transactions sent.\n"
            "                   \"receive\"               Non-coinbase transactions received.\n"
            "                   \"generate\"              Coinbase transactions received with more than 100 confirmations.\n"
            "                   \"immature\"              Coinbase transactions received with 100 or fewer confirmations.\n"
            "                   \"orphan\"                Orphaned coinbase transactions received.\n"
            "      \"amount\" : x.xxx,                 (numeric) The amount in " + CURRENCY_UNIT + "\n"
            "      \"label\" : \"label\",              (string) A comment for the address/transaction, if any\n"
            "      \"vout\" : n,                       (numeric) the vout value\n"
            "      \"fee\": x.xxx,                     (numeric) The amount of the fee in " + CURRENCY_UNIT + ". This is negative and only available for the \n"
            "                                           'send' category of transactions.\n"
            "      \"abandoned\": xxx                  (bool) 'true' if the transaction has been abandoned (inputs are respendable). Only available for the \n"
            "                                           'send' category of transactions.\n"
            "    }\n"
            "    ,...\n"
            "  ],\n"
            "  \"hex\" : \"data\"         (string) Raw data for transaction\n"
            "}\n"
                },
                RPCExamples{
                    HelpExampleCli("gettransaction", "\"1075db55d416d3ca199f55b6084e2115b9345e16c5cf302fc80e9d5fbf5d48d\"")
            + HelpExampleCli("gettransaction", "\"1075db55d416d3ca199f55b6084e2115b9345e16c5cf302fc80e9d5fbf5d48d\" true")
            + HelpExampleRpc("gettransaction", "\"1075db55d416d3ca199f55b6084e2115b9345e16c5cf302fc80e9d5fbf5d48d\"")
                },
            }.ToString());