Improve OptimizelyConfig instantiation performance

[alexZielonko]

How would the enhancement work?

Reduce the number of times that the OptimizelyConfig's instantiation iterates over the datafile's feature flag list.

Current State Summary

1. The OptimizelyConfig instance iterates over each feature flag in a datafile when the constructor calls OptimizelyConfig.getFeaturesMap
2. getDeliveryRules is called during each iteration, which in turn calls getVariableIdMap
3. getVariableIdMap iterates over each feature flag and each feature flag's variables

That is, each feature flag iteration in getFeaturesMap incurs another complete iteration of the feature flags when creating the variablesIdMap.

Due to the nested loop, creating an OptimizelyConfig instance with a hypothetical datafile containing 100 feature flags iterates over the entire feature flag list over 10,000 times.

👈 For reference, here's the complete logic flow

1. Constructor calls OptimizelyConfig.getFeaturesMap

javascript-sdk/packages/optimizely-sdk/lib/core/optimizely_config/index.ts

Line 79 in 2580ea0

this.featuresMap = OptimizelyConfig.getFeaturesMap(configObj, featureIdVariablesMap, experimentsMapById);

2. getFeaturesMap iterates over each feature flag

javascript-sdk/packages/optimizely-sdk/lib/core/optimizely_config/index.ts

Lines 399 to 405 in 2580ea0

	static getFeaturesMap(
	configObj: ProjectConfig,
	featureVariableIdMap: FeatureVariablesMap,
	experimentsMapById: OptimizelyExperimentsMap
	): OptimizelyFeaturesMap {
	const featuresMap: OptimizelyFeaturesMap = {};
	configObj.featureFlags.forEach((featureFlag) => {

3. OptimizelyConfig.getDeliveryRules is called during each feature flag iteration

javascript-sdk/packages/optimizely-sdk/lib/core/optimizely_config/index.ts

Lines 425 to 427 in 2580ea0

	const rollout = configObj.rolloutIdMap[featureFlag.rolloutId];
	if (rollout) {
	deliveryRules = OptimizelyConfig.getDeliveryRules(

4. getDeliveryRules calls OptimizelyConfig.getVariableIdMap

javascript-sdk/packages/optimizely-sdk/lib/core/optimizely_config/index.ts

Line 307 in 2580ea0

const variableIdMap = OptimizelyConfig.getVariableIdMap(configObj);

5. getVariableIdMap iterates over all of the feature flags again & each of the feature flag's variables

javascript-sdk/packages/optimizely-sdk/lib/core/optimizely_config/index.ts

Lines 281 to 291 in 2580ea0

	static getVariableIdMap(configObj: ProjectConfig): { [id: string]: FeatureVariable } {
	let variablesIdMap: { [id: string]: FeatureVariable } = {};
	variablesIdMap = (configObj.featureFlags || []).reduce((resultMap: { [id: string]: FeatureVariable }, feature) => {
	feature.variables.forEach((variable) => {
	resultMap[variable.id] = variable;
	});
	return resultMap;
	}, {});
	return variablesIdMap;
	}

---

Proposed State

My familiarity with the optimizely-sdk's internals is limited. Based on this narrow understanding, I see a couple of ways to reduce the number of times that the OptimizelyConfig iterates over the feature flag list.

👈 One option - Create a single variablesIdMap in the constructor

The constructor iterates over the features flags to generate the featureIdVariablesMap. This reducer's callback could be extended to simultaneously create a single variablesIdMap. The variablesIdMap can then be passed to the getFeaturesMap call, considerably reduceing the variablesIdMap function's overhead.

javascript-sdk/packages/optimizely-sdk/lib/core/optimizely_config/index.ts

Lines 72 to 75 in 2580ea0

	const featureIdVariablesMap = (configObj.featureFlags || []).reduce((resultMap: FeatureVariablesMap, feature) => {
	resultMap[feature.id] = feature.variables;
	return resultMap;
	}, {});

👈 Another option - Use the featureVariableIdMap to pass a specific feature's variables directly to getVariableIdMap

As getDeliveryRules has both the featureVariableIdMap and featureId, the feature's variables can be passed directly to getVariableIdMap. This removes the need to iterate over the entire feature flag list.

javascript-sdk/packages/optimizely-sdk/lib/core/optimizely_config/index.ts

Lines 301 to 304 in 2580ea0

	static getDeliveryRules(
	configObj: ProjectConfig,
	featureVariableIdMap: FeatureVariablesMap,
	featureId: string,

This enhancement might look something like,

  static getDeliveryRules(
    configObj: ProjectConfig,
    featureVariableIdMap: FeatureVariablesMap,
    featureId: string,
    experiments: Experiment[]
  ): OptimizelyExperiment[] {
    // Call `getVariableIdMap` with `featureVariableIdMap[featureId]`, an array of the feature's variables
    const variableIdMap = OptimizelyConfig.getVariableIdMap(featureVariableIdMap[featureId]);

  static getVariableIdMap(featureVariables: FeatureVariable[]): { [id: string]: FeatureVariable } {
    let variablesIdMap: { [id: string]: FeatureVariable } = {};

    // Iterate over the `featureVariables` rather than the entire datafile's feature flag list
    variablesIdMap = (featureVariables || []).reduce((resultMap: { [id: string]: FeatureVariable }, variable) => {
      resultMap[variable.id] = variable;
      return resultMap;
    }, {});

    return variablesIdMap;
  }

When would the enhancement be useful?

This is a useful performance enhancement for all @optimizely/javascript-sdk users, but particularly those with a large number of feature flags in their datafile.

[opti-jnguyen]

Hi @alexZielonko - thanks for bringing up this enhancement proposal, love the formatting and I agree that we should be consolidating redundant iterations.

Will chat with the team on this to set up a time to double check that the enhancement proposed looks good; will follow up here afterwards. Thanks!

[Lithium366]

Thank you @opti-jnguyen if it works this fix should help a lot with performance!

[alexZielonko]

hello @opti-jnguyen! I really appreciate you looking into this. Are there any updates from your team's end?

[opti-jnguyen]

@alexZielonko - hey! Sorry for the lack of communication; the team's been busy prepping for a major version update of the JS SDK. We're planning on diving into this issue after v5.0.0 releases so will provide an update after the dust settles there. Unfortunately, cannot provide an exact ETA at this time, though I can say that we are looking for a v5.0.0-beta release within the next week or so.

If you need the changes sooner, however, I would recommend forking this repository, base a branch off of v4.9.3, and manually apply your suggested changes there. If you have any further Qs, feel free to drop them below - thanks for your patience!

[alexZielonko]

@opti-jnguyen Thank you for following up with this additional information. I am disappointed to learn that you're unable to prioritize customer impacting performance issues in your SDK.

Maintaining a separate fork of vendor software isn't a pragmatic technical decision, and it inadequately resolves this issue.

Please keep me informed of any prioritization updates, as I am eager to see these improvements incorporated into the SDK.

[russell-loube-optimizely]

Hi @alexZielonko , I wanted to provide an update. One of our engineers has evaluated your proposed solutions. Both are technically viable and would achieve desired performance improvements. I'd like to discuss with our team this week to pick an implementation approach.

I'll respond here with any timeline updates once we size this effort and get started in earnest. Thank you.

[russell-loube-optimizely]

Hi again @alexZielonko , quick update - we have a PR open to implement the first option you shared with us currently in code review.

[alexZielonko]

Hello @russell-loube-optimizely thank you for the update. I'm looking forward to this performance enhancement and will keep an eye on the pull request.

[alexZielonko]

@russell-loube-optimizely I reviewed your team's PR and noticed another potential performance enhancement. Please encourage them to consider the suggestion proposed in this comment, #828 (comment).

[russell-loube-optimizely]

Hey @alexZielonko , thanks for reviewing and partnering with us on this. I see @raju-opti responded and agrees it's a sensible change.

I'll be in touch in the near future r/e delivery timelines.

[russell-loube-optimizely]

Hi @alexZielonko , you can find this performance enhancements in Release 4.9.4! We appreciate your collaboration on the change.

I'll go ahead and close this. Please let us know if any questions or concerns.