getDerivedShaderProgram performance issue

I’m using Cesium to render 1000’s of billboards. I’ve made some optimizations regarding entities. The issue I have now is that ShaderCache.prototype.getDerivedShaderProgram is consuming a lot of CPU do to it’s underlying use of js:AtomizeString. As it turns out the following code
var derivedKeyword = keyword + cachedShader.keyword;
seems to be the culprit. ‘cachedShader.keyword’ is a 28K string. This is causing js:AtomizeString to spend a lot of time on that alone.
Is there any way to disable the cache or can someone think of another workaround?

Came up with a solution. I created a very simple lookup table for cachedShader.keyword that maps the 28k string to an index. The lookups are MUCH faster now.