![]() In the article, it was noted that tables that are joined have to bring the data across the wire to a common location in order to perform the join. It states that the optimizer evaluates the query locally even for the remote objects being fetched via the linked server. The article makes no claims about whether the predicate will be performed or not. In Randy’s words, “We've assembled a great team of SQL Server Consultants at SQL Solutions Group, and we have the talent to tackle anything." In addition to getting elbow-deep in data, Randy enjoys taking part in and presenting at SQL Server events nationwide, including SQLSaturday, User Groups, SQL PASS Rally and SQL PASS Summit. Prior to founding SSG, he spent many years as a Database Administrator in a variety of industries, including financial services, telecommunications, and with well-known dot com properties.Īs a data professional, Randy says he has done lots of fun stuff, encountering the most interesting data during his time as database architect for (and no, he didn’t meet his wife while working there). In addition, he has numerous Novell, Microsoft, and Cisco legacy certifications. In 2020 he completed certification for Azure Fundamentals. Randy is a Microsoft Certified Solutions Master in SQL Server 2008. His prowess with SQL Server earned him the label “database whisperer” from one satisfied customer. Randy has a passion for solving what can seem to others to be insurmountable problems. ![]() Randy Knight, a Microsoft Certified Master, founded SQL Solutions Group in October 2010, after more than 20 years in the technology industry. I have “fixed” queries that were taking 12+ hours to run and reduced the time to just minutes by making this simple change to the code. The inefficient table scan plus bringing all that over the network so that it can be filtered locally. This is a simple example, but imagine if the remote table had a million plus rows. Note that this is remotely executing so if the server was to another DBMS, you’d want the query written in that engine’s flavor of SQL. The remote server to execute the query on, and the query itself. Essentially what we are doing is executing a remote query on the linked server and just asking for the results back. In addition, all of the data will be sent across the network only to be filtered for Gender on the local system.Ī better way to do this is to use a function like OPENQUERY(). ![]() So this query will result in a table scan, every time, regardless of remote indexes. There may well be an index on Gender which could be taken advantage of, but the local optimizer has no way to know that. But it doesn’t know anything about indexes and statistics that exist on the Employee table on the remote server. In this case, the optimizer on the local server will determine the execution plan. To understand this, you need to always ask the following question: “Where will the query be optimized?” While this is the most popular way to use Linked Servers, it is also the worst way in terms of performance. The most common way to do this is to use four part names to refer to objects on the remote server.įROM Now that we have a linked server set up, we can access it from the local SQL Server instance. SQL Solutions Group, we do your database dirty The security implications of these choices are beyond the scope of this post but the most important thing is that in most cases Options 2 and 4 should not be used. I could also choose to always use a certain security context or to map local login’s to remote logins. In this case, I am saying to just pass through the login’s security context to the remote server. I prefer this practice because you can use the same linked server name in multiple environments (Development, QA, Production, etc.)Īuthentication settings have to be configured as well. It does not have to be the name of the instance. Note that the Linked Server name can be whatever we want it to. This allows us to use the linked server name ADVENTUREWORKS to access the AdventureWorks database on the instance RKLAPTOPSS. We configure a linked server by specifying the remote data source and a name for the sever. To start with, lets look at how a linked server works. In this article we’ll take a look at using linked servers the right way (and a few wrong ones). Linked Servers are a very popular way to access distributed data in environments with lots of SQL Server instances on different serves, or even on other Database Management Systems like Oracle or MySQL. While linked servers can be very useful if used correctly, I have found that more often than not, they are not used correctly and are a source of lots of performance problems.
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