It's a tradeoff. Open addressing is faster due to cache locality, but needs a good hash function. If the hash function tends to cluster values and generate coll

It's a tradeoff. Open addressing is faster due to cache locality, but needs a good hash function. If the hash function tends to cluster values and generate collisions you might (key word here "might", as usual you need to do profiling to check each case) end up with way more operations per query. But for 90% of cases, you don't really care that much about performance and whether it's open or closed addressing, as long as the mapping works.