Question about dynamic pages and google

I know that dynamic pages get indexed by Google.
My question is:
Does google only hold the url data or also the dynamic contents that loads in the page.
In other words: if I have my dynamic pages created based on the _id field, will it be meaningless from the searcher point of view (because the ID is only a random sequence) or maybe the dynamic contents also appear in Google search results somehow.
Thank you!

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