Check also PHP-7 or 8's "open addressing" hash map. Beats the hell out of everyone else. Like C++ red-black tree default hashmap implementation taking 1.0 second -- vs PHP taking 0.5 second for the same dataset.

Here's the code I tested with.

php:

  #!/usr/bin/env php
  <?
  $ret=[];
  for($i=0; $i<5000000; $i++){
   $ret["id.".($i%500000)]="val.".$i;
  }
  print(count($ret))."\n";
  print $ret["id.10000"]."\n";

cpp:

  #include <iostream> 
  #include <map> 
  using namespace std; 
  
  int main(){ 
   map<string, string> ret; 
   for(int i=0; i<5000000; i++){
    ret[string("id.")+to_string(i%500000)] = string("val.")+to_string(i); 
   }
   cout << ret.size() << endl;
   cout << ret["id.10000"] << endl;
   return 0;
  }

Rust :

  use std::collections::HashMap;
  fn main(){
    let mut ret = HashMap::new();
    for i in 0..5000000 {
        ret.insert(format!("id.{}", i%500000), format!("val.{}",i));
    }
    println!("{}", ret.len());
    match ret.get("id.10000") {
        Some(val) => println!("{}", val),
        None => println!("ERROR")
      }
  }