## The problem
Issue optimizely/javascript-sdk#817 (closed, 12 comments): building OptimizelyConfig redundantly iterated the datafiles feature flag list, which hurt on big datafiles. The reporter proposed consolidating the loops; the maintainers agreed, opened a PR implementing it, and shipped the improvement in release 4.9.4.
## What fixed it
Slow OptimizelyConfig construction on large datafiles was a real SDK perf bug, fixed in 4.9.4 by removing the redundant iterations over the feature flag list. If you are on an older 4.x, upgrade to 4.9.4 or later. Creating one long-lived client instance instead of one per request also avoids paying the construction cost repeatedly.