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
```

change_position = options["changePosition"].get_int();
        if (options.exists("change_type")) {
            if (options.exists("changeAddress")) {
                throw JSONRPCError(RPC_INVALID_PARAMETER, "Cannot specify both changeAddress and address_type options");
            }
            coinControl.m_change_type = pwallet->m_default_change_type;
            if (!ParseOutputType(options["change_type"].get_str(), *coinControl.m_change_type)) {
                throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, strprintf("Unknown change type '%s'", options["change_type"].get_str()));
            }
        }
        if (options.exists("includeWatching"))
            coinControl.fAllowWatchOnly = options["includeWatching"].get_bool();
        if (options.exists("lockUnspents"))
            lockUnspents = options["lockUnspents"].get_bool();
        if (options.exists("feeRate"))
        {
            coinControl.m_feerate = CFeeRate(AmountFromValue(options["feeRate"]));
            coinControl.fOverrideFeeRate = true;
        }
        if (options.exists("subtractFeeFromOutputs"))
            subtractFeeFromOutputs = options["subtractFeeFromOutputs"].get_array();
        if (options.exists("replaceable")) {
            coinControl.m_signal_bip125_rbf = options["replaceable"].get_bool();
        }
        if (options.exists("conf_target")) {
            if (options.exists("feeRate")) {
                throw JSONRPCError(RPC_INVALID_PARAMETER, "Cannot specify both conf_target and feeRate");
            }
            coinControl.m_confirm_target = ParseConfirmTarget(options["conf_target"]);
        }