Performance of SQL Server vs number of databases - sql-server

Does the number of databases on a SQL Server installation affect performance ?
Lets say I have a multi-tenant application, I have the option of creating a database per tenant or having management table based client table separation or configuration based client table separation.
For 10 clients who are accessing the application, the number of queries are going to be the same regardless of whether I have 10 separate databases or one database.
So does it matter or is there a benefit implementing this one way or the other ?

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How to query multiple databases from different SQL Servers

We have approx. 8 odd SQL Servers used for different purposes like inserting data in 1 server, update in another etc. (or connecting to only that database based on user’s region).
The problem is sometimes query for data needs to be done from multiple SQL Server databases. So say, I have an Id property, and based on the Id data needs to be retrieved from multiple of these 8 servers (if there is an Id match, so basically querying all database).
So basically the server which the user is logged into, will use “Linked Server” functionality and connect to other SQL Servers (with the server which the user is currently on acts as the source SQL Server), and using “UNION” functionality to club all data.
As a lot of transactions is taking place each day, this approach is not feasible, performance wise.
So any recommendations on a better approach to achieve the same above functionality. I read a concept called “Server Groups” but not sure of it.
The application is made in .Net Web Forms using Jquery/Ajax/HTML/API and ADO.NET.
If you have a .net application which is outside these 8 servers can't you establish individual connections and pass the ID from .net app to these servers ?
As far as I know "Server Group" is a concept in SSMS which helps you to group the servers and can run common scripts at same time.

Concentrating multiple MS SQL Servers into one

I have an interesting SQL challenge. I have multiple satellite (potentially in the 100s) of MS SQL express Servers that I need to concentrate into one central SQL Server. The satellite servers are basically logging transactions that occur, basically the usage of a material at a particular time. The central SQL Server will be used for reporting summary reports (e.g the amount of material used per day etc), rather than holding the full data set from each machine. I have a couple of ideas in mind of how to do this (using linked servers on the central server with a view on each satellite server is one, and a SQL task that periodically refreshes the data ). What I am not sure is how would that scale up when I am using multiple satellite servers, what would be the best solution performance wise ?
You can simply use the linked server queries. (format: server_name.database_name.schema_name.table_name)
Since your expectation is only to generate summary reports, you can create the required view / procedure definitions inside this one central SQL server without storing the data from different servers into it.

Multi tenancy - MongoDB vs SQL Server Express

Based on our requirement we need to have one database per account as we cannot have a single database. So we were thinking about multiple database on the SQL Server and based on my research we can have appx 32,000 database on single database instance but the resource limit will be reached far sooner.
How many is too many databases on SQL Server?
Another point was to use no-sql database like MongoDB. As far as I know we can create database per account with different database name.
I wanted to check reference to resources used by MongoDB, do I need more ram, processor and lots of servers for the architecture.
We are looking to have about 10,000 databases max on a server. Can that work on the a single mongodb server?
If you do have similar architecture currently running, please do share.

Should i just use 1 database?

Hi i am building a window apps retailer pos but was wondering what is the best method to design the database. Should i just use 1 database to store all my clients data?
Meaning to say if i have 100 clients from different businesses using my App, all of their data will be stored in 1 database.
e.g. i will store 1 company column in the user table to indicate which company does the customer or transaction belongs to.
My current practice is i create new database for each business and put it installed into their local machine. (Got to manually install sqlserver + sqlexpress).
Do u think it is more easier for me to design in this way? and i can just put the database online to sql server. Will i be getting any latency ? how bad will it be? I heard Window Azure able to handle this well. In my case i think the speed and data size per business is not really a concern.
Could you advice?
You should definitely look at other alternatives within Azure for storing data, specifically Azure Storage Tables and Blobs.
Utilizing all of the Azure Storage Options with SQL Azure will allow you to choose different data tiers depending on your application's needs and your desired cost structure. Running everything inside of SQL Azure will cost you more in the long run, but it makes a good place to tie together federated data for relational reporting, whereas you can store each tenant's data inside of Azure Tables, using PartitionKeys which keep each client's data separated from the others.

How to automatically synchronize tables in different databases

Little background: I'm working in a large company with a lot of branches. We have several applications with separated databases sometimes on different servers. But every database contains a table with a list of branches and their relationships. I want to automatically synchronize these tables when one of them changed.
My question is: what are the best practices of automatic synchronization of tables in different databases (Microsoft SQL Server 2008)?
Are there sql server features for that purpose? Or external tool is a good way? Or it's better to write a small application and run it as a service or use the scheduler?
You can use replication (a SQL server built-in feature) to synchronize different databases.
You can also use triggers or log shipping to sync your tables as records are added ,updated or deleted:
Here are some links about replication.
Here are some links about log shipping.

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