Performance with n Indices in Aliases

I was wondering what is going on behind the scenes when adding n number of
indices to an alias. Are there any performance implications?

So an alias with a single index that has a single shard will allocate a
single process to scan the index... So that would mean, with the same
data, when having two indices each with a single shard in an alias it would
require two processes in parallel to scan the index. The key being the
scan time is but in ~half due since there are two processes scanning half
the data. This scales to the point of thread saturation. The performance
is then affected by number and power of cores...

I'm wondering if there is a significant difference performance in using an
alias with 100 indices or even 10,000 vs an alias with a single index (on a
single core machine)?

What impacts are there to the performance and considerations one must take?

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