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Overview | Anatomy of a Query Plan | Reading a Query Plan | Configuring Query Plans | Optimizing Queries
An Omnidex query plan is designed to provide all of the essential information needed to understand how a query will be processed, as well as basic suggestions about how to further optimize the query. A great deal can be learned by reviewing the query plan, and it is always the first step in understanding Omnidex query performance.
A query plan consists of two sections: the Summary and the Details. The Summary section shows the SQL statement, the version of Omnidex, any optimization settings or warnings that affect the query, and even occasional suggestions for optimizing the query. The Details section shows the steps that will be executed to satisfy the query. Steps are executed in the order displayed, and are indented as needed to show loops of instructions. The example below shows the skeleton of a query plan:
----------------------------------- SUMMARY ----------------------------------- <SQL Statement> Version: <Omnidex version> Request Opt: <Requested optimization settings> Optimization: <Actual optimization settings> Warnings: <Warning flags> Notes: <Optimization notes> ----------------------------------- DETAILS ----------------------------------- <Query processing step 1> <Query processing step 2> <Query processing step 3> ... -------------------------------------------------------------------------------
The Summary section describes the SQL Statement and provides general notes and flags about the query. These included optimization settings and recommendations. The Summary section is the first place to look when evaluating the optimization of a query.
The SQL Statement being explained is shown, formatted for easy viewing.
The version of Omnidex, including the compilation timestamp. This is important as optimization can be different between versions of Omnidex.
If specific optimization was required when the query was run, then these settings are shown here. If no special optimization was required, then this line is omitted.
The specific optimizations that can be required are:
| Setting | Description |
|---|---|
| Setting | Description |
| NO_XREF_FILES | Do not create Cross-Reference files when processing this query. Cross-Reference files are sometimes used to optimize complex, many-to-many table relationships, but they generally cause a query to take a lot of time, especially on large databases. |
| NO_UNOPTIMIZED_CRITERIA | Do not allow any criteria to be processed without the use of Omnidex indexing. |
| NO_CARTESIAN_PRODUCTS | Do not allow Cartesian Joins. Cartesian Joins occur when tables are joined together without any join criteria. While there are rare cases when Cartesian Joins are desireable, they are usually an indication of missing join criteria. |
| NO_UNOPTIMIZED_AGGREGATIONS | Do not allow any aggregations to be processed without the use of Omnidex indexing. |
| NO_UNOPTIMIZED_SORTS | Do not allow any sorts to be processed without the use of Omnidex indexing. |
| NO_SEQUENTIAL_SCANS | Do not allow any sequential table scans. |
| NO_SEQUENTIAL_TABLE_JOINS | Do not allow any sequential table joins. A sequential table join indicates that all rows in the second table will be scanned sequentially for each row in the first table. This is the most inefficient way to perform a join, and is only necessary when Omnidex indexing, underlying database indexing, table caching and sort/merging cannot be used. |
| NO_GRID_AGGREGATIONS | Do not allow any aggregations to be performed on the grid controller that require reaggregating data on the grid controller. |
See also: