When you have multiple sources requesting the same index creation, the following occurs:

• Since the index doesn't exist yet, each index build starts
• Once the first index creation finishes, index now shows up
• Remaining index builds have to complete before checking and validating that they built for nothing since the index now exists.

We saw this issue with an application requesting new index creation. After deploying un update to 50+ servers, they all made the same request on a particularly large index, which effectively took down the database servers.