Understanding SQL Server Cache I have a tricky question and I do not exactly know where to find relevant information to this.

I have SQL Server 2014 Enterprise installed on a database server. On this server there exist multiple databases, some belong to us and some to other companies. 

My concern is with cache memory. I have a basic understanding of how SQL Server uses cache memory to retrieve data pages fast. You run a query, and usually, data pages get loaded to the cache and with repeatable calls, it gets results from this.  

But... our application is highly used in usual working hours by our customers but at night there are always maintenance tasks going on. I am assuming (please tell me if I am wrong) that during the day, the cache gets loaded with useful data pages, but at night it is deleted because of the maintenance tasks, and so the next day, when customers start doing transactions, data pages have to be again loaded into the cache first, which takes time and slows a lot of things down. 

So, can I somehow prove if that happens?

If yes, can I manage it? Such as somehow telling SQL Server to not load into cache?

I would be grateful for some specific articles discussing this topic. I could not find any, or better say, I do not know how to name this problem.
but at night it is deleted because of the maintenance task


I would not say deleted as more "overwritten" or "evicted". Maintenance may simply use the memory for other things. Not a big issue normally.


  and so a next day, when customers do transactions, data pages have to be again loaded 
  to  Cache, which takes time and slows a lot of things down.


If that is really that brutal the case, you have either an edge case or a hardware problem.

Generally you can preseed the cache by running a number of "maintenance queries" in the early morning (to reload the data into the cache at 0600 in the morning for example) as part of maintenance. I.e. you end it by querying for the data you want loaded into the cache. Problem solved.

But generally this should not result in an EXTREME slowdown - yes, initial requests will be slower, but that should fix itself quite fast as the cache is going to fill up with every query. Is it possible that your experienced slowdown is not "cache" but "morning spike"? There are a lot of systems where at specific times (one of them the morning when people log in and check their work) the load is a lot higher than later during the day. In this case, you need to scale the hardware up to handle this. WOuld be among the first times I would have seen maintenance as a very significant issue.