I did a quick benchmark of lookup time for map vs ets as I am working with a lot of ETL stuff. ets is very convenient as you can communicate with it from other processes just by using named tables. And the performance difference between these doesn’t seem huge (lookup times for ets is 1 to 2x of map lookup times).
Here are the logs for your perusal. The benchmarking code can be found at https://github.com/minhajuddin/lookup_bench . Would love to hear your thoughts 
In the log, the first number is the number of records in the map/ets table and the second number is the number of lookups, so ‘ets_1000_100’ means it has 1000 records in the ets table and we are performing 100 lookups
There is a bug in the code which incorrectly reports the number of lookups when the size of the map/ets table is less than the number of keys, in this scenario the number of lookups is actually equal to the number of keys in the map/ets table
15:05:09.922 [debug] starting benchmark
15:05:09.922 [debug] loading data
Erlang/OTP 19 [erts-8.2] [source-fbd2db2] [64-bit] [smp:8:8] [async-threads:10] [hipe] [kernel-poll:false]
Elixir 1.4.0
Benchmark suite executing with the following configuration:
warmup: 2.0s
time: 5.0s
parallel: 1
inputs: none specified
Estimated total run time: 14.0s
Benchmarking ets_100_100...
Benchmarking map_100_100...
Name ips average deviation median
map_100_100 100.55 K 9.95 μs ±44.35% 10.00 μs
ets_100_100 52.12 K 19.19 μs ±57.85% 17.00 μs
Comparison:
map_100_100 100.55 K
ets_100_100 52.12 K - 1.93x slower
- - -
Benchmarking ets_100_1000...
Benchmarking map_100_1000...
Name ips average deviation median
map_100_1000 99.89 K 10.01 μs ±42.19% 10.00 μs
ets_100_1000 52.50 K 19.05 μs ±55.80% 17.00 μs
Comparison:
map_100_1000 99.89 K
ets_100_1000 52.50 K - 1.90x slower
- - -
Benchmarking ets_100_10000...
Benchmarking map_100_10000...
Name ips average deviation median
map_100_10000 100.04 K 10.00 μs ±40.33% 10.00 μs
ets_100_10000 52.72 K 18.97 μs ±56.81% 17.00 μs
Comparison:
map_100_10000 100.04 K
ets_100_10000 52.72 K - 1.90x slower
- - -
Benchmarking ets_1000_100...
Benchmarking map_1000_100...
Name ips average deviation median
map_1000_100 85.03 K 11.76 μs ±51.86% 11.00 μs
ets_1000_100 45.03 K 22.21 μs ±44.35% 20.00 μs
Comparison:
map_1000_100 85.03 K
ets_1000_100 45.03 K - 1.89x slower
- - -
Benchmarking ets_1000_1000...
Benchmarking map_1000_1000...
Name ips average deviation median
map_1000_1000 8.58 K 116.58 μs ±12.33% 110.00 μs
ets_1000_1000 3.93 K 254.60 μs ±14.07% 247.00 μs
Comparison:
map_1000_1000 8.58 K
ets_1000_1000 3.93 K - 2.18x slower
- - -
Benchmarking ets_1000_10000...
Benchmarking map_1000_10000...
Name ips average deviation median
map_1000_10000 8.74 K 114.38 μs ±11.29% 108.00 μs
ets_1000_10000 3.94 K 253.52 μs ±14.61% 247.00 μs
Comparison:
map_1000_10000 8.74 K
ets_1000_10000 3.94 K - 2.22x slower
- - -
Benchmarking ets_10000_100...
Benchmarking map_10000_100...
Name ips average deviation median
map_10000_100 72.80 K 13.74 μs ±102.80% 13.00 μs
ets_10000_100 41.67 K 24.00 μs ±39.73% 22.00 μs
Comparison:
map_10000_100 72.80 K
ets_10000_100 41.67 K - 1.75x slower
- - -
Benchmarking ets_10000_1000...
Benchmarking map_10000_1000...
Name ips average deviation median
map_10000_1000 5.89 K 169.64 μs ±31.67% 151.00 μs
ets_10000_1000 3.04 K 329.03 μs ±14.20% 322.00 μs
Comparison:
map_10000_1000 5.89 K
ets_10000_1000 3.04 K - 1.94x slower
- - -
Benchmarking ets_10000_10000...
Benchmarking map_10000_10000...
Name ips average deviation median
map_10000_10000 583.12 1.71 ms ±26.31% 1.48 ms
ets_10000_10000 269.62 3.71 ms ±33.27% 3.04 ms
Comparison:
map_10000_10000 583.12
ets_10000_10000 269.62 - 2.16x slower
- - -
Benchmarking ets_100000_100...
Benchmarking map_100000_100...
Name ips average deviation median
map_100000_100 43.00 K 23.26 μs ±1400.38% 14.00 μs
ets_100000_100 42.37 K 23.60 μs ±39.66% 21.00 μs
Comparison:
map_100000_100 43.00 K
ets_100000_100 42.37 K - 1.01x slower
- - -
Benchmarking ets_100000_1000...
Benchmarking map_100000_1000...
Name ips average deviation median
map_100000_1000 3.01 K 332.13 μs ±323.60% 210.00 μs
ets_100000_1000 2.75 K 363.27 μs ±15.39% 355.00 μs
Comparison:
map_100000_1000 3.01 K
ets_100000_1000 2.75 K - 1.09x slower
- - -
Benchmarking ets_100000_10000...
Benchmarking map_100000_10000...
Name ips average deviation median
map_100000_10000 232.37 4.30 ms ±66.78% 3.48 ms
ets_100000_10000 149.05 6.71 ms ±33.43% 5.88 ms
Comparison:
map_100000_10000 232.37
ets_100000_10000 149.05 - 1.56x slower
- - -
Benchmarking ets_1000000_100...
Benchmarking map_1000000_100...
Name ips average deviation median
map_1000000_100 39.71 K 25.18 μs ±4145.59% 15.00 μs
ets_1000000_100 36.51 K 27.39 μs ±107.98% 23.00 μs
Comparison:
map_1000000_100 39.71 K
ets_1000000_100 36.51 K - 1.09x slower
- - -
Benchmarking ets_1000000_1000...
Benchmarking map_1000000_1000...
Name ips average deviation median
map_1000000_1000 2.88 K 347.20 μs ±953.55% 251.00 μs
ets_1000000_1000 2.42 K 413.69 μs ±21.88% 401.00 μs
Comparison:
map_1000000_1000 2.88 K
ets_1000000_1000 2.42 K - 1.19x slower
- - -
Benchmarking ets_1000000_10000...
Benchmarking map_1000000_10000...
Name ips average deviation median
map_1000000_10000 181.11 5.52 ms ±218.75% 4.46 ms
ets_1000000_10000 138.43 7.22 ms ±12.59% 7.09 ms
Comparison:
map_1000000_10000 181.11
ets_1000000_10000 138.43 - 1.31x slower
