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Indexes on columns

SQL 7. In the table sysindexes, under the 'name' column, we see many indexes that begin with '_WA_Sys'. What are these? Example: We have a table that has 2 indexes and there are 24 of these '_WA_Sys' indexes for every field in the table not used in our 2 indexes.

This is a manifestation of the new dynamic configuration that exists in SQL Server 7.0 or later. You create indexes on colums to improve the data access. Previously, you had to do a lot of monitoring as data and access patterns change over time. This meant you had to either create new indexes or realign old ones. SQL Server 7.0 tracks the access patterns that are being used. If an index doesn't exist on a column that would have benefitted a query, SQL Server will create its own on the fly. These are not true indexes, but instead are statistics that SQL Server created on the fly to satisfy a query just as an index would do.

 

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