Opensearch index mapping for single or dual

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:wave::skin-tone-2: Hello, team!
I’m working on structuring the search index for millions of items, each with available quantities at the fulfillment-center level. I’m evaluating approaches that preserve full filtering and sorting capabilities on all indexed fields with affecting performance
I’d appreciate your thoughts on whether a single index or separate indexes for item data and fulfillment-center inventory would be more appropriate.

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