Custom Block – Unique Identifier

Is there is a unique identifier that can be used in the block (There isn’t anything in the $options variable).

From my understanding (at least with what I read about WordPress shortcodes being generated for each individual email) is that If I create a block that has a MySQL query in it, that it would run that query for each email that is being generated (let me know if I’m wrong). My list is over 50,000 subscribers so I could see this adding a lot of processing on the server, I would like to save the query in memory to be retrieved but I’m looking at adding a unique identifier to it (I can create my own, just thought there may already be something in place that could be used).