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table variable vs temp table performance

por   |   diciembre 28, 2020

Before you continue reading this blog post I suggest you read the following blog posts: SQL SERVER – Regular Table or Temp Table – TempDB Logging Explained; SQL SERVER – Regular Table or Temp Table – A Quick Performance Comparison Temporary tables and table variables, both have their own pros and cons. I have a table named testmember with 1.5 million records. I have previously blogged about it here: SQL SERVER – Table Variables or Temp Tables – Performance … Table variable, #temp tables will snag when volume of data increases. In my experience of taking an average of all queries that have used #temp tables vs @table variables, the temp tables have come out on top. These are automatically deleted when the session that created the tables has been closed. In this blog post, we will talk about Performance Comparison between Table Variable or Temp Table. Most of the time I see the optimizer assume 1 row when accessing a table variable. Local Temp Table. This article describes: Scenarios which argue in favor of conversion to In-Memory. I tried the following to check the performance perspective of table variables and temp tables. Whereas, a Temporary table (#temp) is created in the tempdb database. This can mostly be seen when there is a lot of data. The code changes are usually minimal. If you use temporary tables, table variables, or table-valued parameters, consider conversions of them to leverage memory-optimized tables and table variables to improve performance. The time needed to execute the select alone is ~10 seconds. The real problem with the temporary table is there when we are reading more than a certain amount of the rows in the SQL Server. 2 Comments ... Of course, such an assumption can make a huge impact on performance when a suboptimal query plan is used on a large table. We tested #temp, table variables in our environment with a data volume of 600 million, Permanent temporary table created in user databases will give outstanding performance. I could see that Temp tables are quite faster than table variables if we load numerous records. However with <10000 records being loaded, the table variables were much faster than temp tables. The temp table version takes up to 10 seconds to execute, I had to stop the table variable version after 5 minutes. A workaround is to use the OPTION (RECOMPILE) hint. CTE, table variables, #temp tables are suitable only for small volume of data. Table variables use tempdb similar to how temporary tables use tempdb. Table variables are not in-memory constructs but can become them if you use memory optimized user defined table types. From [table (Transact-SQL) on MSDN][1]: >**Important** >Queries that modify table variables do not generate parallel query execution plans. Often I find temporary tables to be a much better choice than table variables. The temporary table doesn't have any keys or indexes, the select part is the same between the 2 queries, and the number of results returned by the select is ~10000 rows. We need to decide which one to use and when. Table variables are persisted just the same as #Temp tables. Since @table variables do not have statistics, there is very little for the optimizer to go on. The main performance affecting difference I see is the lack of statistics on table variables. In these situations, consider using temporary tables … The local temporary table name … ⇒ Table variable (@table) is created in the memory. Performance. The reason is that the query optimizer will sometimes generate poor plans for @table vars. Local temp tables are only available to the SQL Server session or connection (means single user) that created the tables. Let us compile the list for differences. 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