Extra memory consumption in ramping-arrival-rate if big map is used

[mkosta]

Brief summary

Noticed in ramping-arrival-rate executor that if the big map is filled at init stage and then used in the function, memory consumption is jumping to 10% per thread compared to 1% if the map is filled in the function. There are different scenarios and ration is not necessary 1 to 10, in some cases worse. For example increasing pre allocated vus x2 will increase memory per thread x2 times.

execute this strip down version of script and then comment out eventIdsMap in init stage and uncomment in default function and watch the difference in htop or whatever memory monitoring tool

  let eventIdsMap = generateEventIds(100000);
  
  export const options = {
    scenarios: {
      contacts: {
        executor: 'ramping-arrival-rate',
  
        // Start iterations per `timeUnit`
        startRate: 5000,
  
        // Start `startRate` iterations per minute
        timeUnit: '10m',
  
        // Pre-allocate necessary VUs.
        preAllocatedVUs: 250,
  
        stages: [
          { target: 5000, duration: '10m' },
          { target: 6000, duration: '20m' },
          { target: 6000, duration: '40m' },
          { target: 60, duration: '20m' },
        ],
        exec: "default"
      },
    },
  };

  export default () =>
  {
    //let eventIdsMap = generateEventIds(100000);    
    
        let randomIntEventId = Array.from(eventIdsMap.keys())[
        randomIntBetween(0, eventIdsMap.size-1)
        ]; //take random key
    
        console.log(randomIntEventId);  
  };

  export function generateEventIds(maxEventIds) {
    let dataMap = new Map();
  
    for (let i = 1; i <= maxEventIds; i++) {
      dataMap.set(i, i); //key, eventId
    }
    return dataMap;
  }
  
  export function randomIntBetween(min, max) {
    return Math.floor(Math.random() * (max - min + 1) + min);
  }

init stage map fill default function map fill

k6 version

0.50

OS

ubuntu 22.04

Docker version and image (if applicable)

No response

Steps to reproduce the problem

execute this strip down version of provided script and then comment out eventIdsMap in init stage and uncomment in default function and watch the difference in htop or whatever memory monitoring tool

Expected behaviour

memory should not be consumed at this level. in my understanding init stage should share the map and filling 100k map for each iteration should be worse than filling it in init stage

Actual behaviour

for this particular executor there is this problem with massive memory usage when the map is around 100k the bigger the worse. other executors i tried like shared iterations, pervuiterations on comparable rps are consuming little memory