Demonstation of how sharded db can reduce load

dbTest.js

function roundRobin(count, shardCount) {
  const shards = new Array(shardCount).fill(0);
  function hitShard(shard, key) {
    shards[shard]++;
    const mod = key % shards.length;
    if (mod !== shard) {
      hitShard(mod, key);
    }
  }
  let idx = 0;
  for (let i = 0; i < count; i++) {
    const num = Math.round(Math.random() * 100);
    hitShard(idx++ % shards.length, num);
  }
  const total = shards.reduce((accum, curr) => accum + curr, 0);
  return {
    shards,
    total,
    max: shards.reduce((last, curr) => (curr > last ? curr : last)),
    average: total / shardCount
  };
}

function test(count, shardCount, iterations) {
  const results = new Array(iterations);
  for (let i = 0; i < iterations; i++) {
    results[i] = roundRobin(count, shardCount);
  }
  return {
    max: results.reduce((accum, curr) => accum + curr.max, 0) / iterations,
    average:
      results.reduce((accum, curr) => accum + curr.average, 0) / iterations,
    total: results.reduce((accum, curr) => accum + curr.total, 0) / iterations
  };
}
const testCases = [[10, 1], [10, 2], [10, 5], [100, 3], [100, 5], [100, 15]];

for (const testCase of testCases) {
  console.log(`count: ${testCase[0]}`, `shardCount: ${testCase[1]}`,  test(...testCase, 100));
}

results

• count: 10, shardCount: 1, {max: 10, average: 10, total: 10}
• count: 10, shardCount: 2, {max: 8.12, average: 7.47, total: 14.94}
• count: 10, shardCount: 5, {max: 5.17, average: 3.63, total: 18.13}
• count: 100, shardCount: 3, {max: 59.39, average: 55.53, total: 166.59}
• count: 100, shardCount: 5, {max: 40.49, average: 35.91, total: 179.53}
• count: 100, shardCount: 15, {max: 17.74, average: 12.88, total: 193.26}