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Trying to figure out why there is such a significant difference between
select * from linkedserver..tablename
and
select * from openquery(linkedserver, select * from tablename).
4 minutes vs 13 seconds.
886
The OPENQUERY is faster than the linked server because when we use the linked server, the SQL Server breaks the query into local and remote queries. The local queries are executed on the local server, and remote queries will be sent to the remote server.
Executes the specified pass-through query on the specified linked server. This server is an OLE DB data source. OPENQUERY can be referenced in the FROM clause of a query as if it were a table name. OPENQUERY can also be referenced as the target table of an INSERT, UPDATE, or DELETE statement.
Executing a query against views on a linked server remotely takes more time than executing the same query directly against a base table on the linked server.
The alternative to using Linked Servers is to use the OPENQUERY statement, also known as a pass through query. When using an OPENQUERY statement, the WHERE clause gets executed at the remote server and the resultant (mapped) records traverse over the wire instead of an entire sourced data set.
OPENQUERY connects to the destination server and runs the query on that server and returns the resultset. Whereas, I believe the Linked Server query is executed on the local server and runs across the connection.
Hope this helps.
161
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