Fixes experimental_approximateDocumentStoreMiB

[owenallenaz]

The ApolloServer documentation calls out a setting for experimental_approximateDocumentStoreMiB allowing you to set max size of the internal documentStore.

Current code for initializeDocumentStore:

private initializeDocumentStore(): InMemoryLRUCache<DocumentNode> {
    return new InMemoryLRUCache<DocumentNode>({
      // Create ~about~ a 30MiB InMemoryLRUCache.  This is less than precise
      // since the technique to calculate the size of a DocumentNode is
      // only using JSON.stringify on the DocumentNode (and thus doesn't account
      // for unicode characters, etc.), but it should do a reasonable job at
      // providing a caching document store for most operations.
      maxSize:
        Math.pow(2, 20) * (this.experimental_approximateDocumentStoreMiB || 30),
      sizeCalculator: approximateObjectSize,
    });
  }

That code relies on this.experimental_approximateDocumentStoreMiB , but that variable is never set in the constructor. This PR fixes that.

That being said, I would actually like to go one step further, to allow passing a custom documentStore as part of the constructor. One of our graphql server processes maintains 20 different ApolloServer that host different versions of schema-stitched APIs (cms-v1, cms-v2, cms-v3, dms-v1 etc). It would be nice if I could re-use the document store between all of those instances since there is considerable overlap in the queries between the different versions of the graphql servers. Right now it gobbles up memory because we end up with 30mb x 20 servers. I didn't want to do that step, because that's really more of a feature request, but I'd be willing to update this PR, or spin a new one to include that functionality if it's acceptable.

[apollo-cla]

@owenallenaz: Thank you for submitting a pull request! Before we can merge it, you'll need to sign the Apollo Contributor License Agreement here: https://contribute.apollographql.com/

[glasser]

Ah, good catch! I would have thought that TS would give a noUnusedLocals error on the declaration of experimental_approximateDocumentStoreMiB but its existence affects the contents of requestOptions.

[glasser]

I'll merge this improvement for now. I think it would be reasonable to offer a new documentStorageCache:KeyValueCache constructor argument, which I think could just replace experimental_approximateDocumentStoreMiB entirely. Are you able to implement that? I think it would be perfectly reasonable to entirely remove an option that is labeled as experimental and has never worked.