* Our tool is totally outside the database server, thereby incurring no overhead of instrumenting
query optimizer's code, which is required by some existing tools [4-6].
SR2 adds several enhancements and refinements to VOD 8.0 including improved
query optimizer now supporting compound indexes, improved horizontal scale out with support of distributed databases, improved production environments due to new online database configuration capabilities, and general multi core performance improvements.
Sections cover foundations, identification of performance problems, the
query optimizer, and optimization.
For example, we will describe the design of a
query optimizer that compiles a query for execution and determines the best possible way among many alternative ways to execute a query.
The crux of the problem is that opportunistic caching of data at sites to which the data has been sent for query processing imposes an additional responsibility on the
query optimizer: operator site selection decisions made for one query have ramifications on the performance of subsequent queries.
Therefore, queries with C functions in the qualification cannot be optimized by the POSTGRES
query optimizer. For example, the preceding query on overpaid employees will result in a sequential scan of all instances of the class.
In addition, the INGRES
query optimizer is acknowledged to be the best, and the company offers an excellent report generator.
One central component of a
query optimizer is its search strategy or enumeration algorithm.
Similarly, the modules User Interface, Application Interface, SQL Parser, and Distributed
Query Optimizer are not used at the data location.