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
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
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
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
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
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
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