Database query optimization

A computer system for improving performance of queries with historically low performance in a big data environment, the computer system comprising:

• a memory;
• and
• one or more processors in communication with the memory, wherein the computer system is configured to perform a method, said method comprising:
• identifying, by the one or more processors, a query with low performance;
• generating, by the one or more processors, a small data environment from the big data environment, the small data environment for use in optimizing the query with low performance, the generating comprising:
• automatically identifying, by the one or more processors, one or more tables and one or more fields for inclusion in the small data environment, wherein each of the identified one or more tables and each of the one or more fields is referenced in the query with the low performance;
• sampling, by the one or more processors, a portion of each table of the identified such that each table in the small data environment comprises common data traits to a whole of each table, the sampling comprising:
• for each table of the identified one or more tables;
• selecting, by the one or more processors, for inclusion in the small data environment, rows in the table comprising fields with outlier values for each of the identified one or more fields;
• selecting, by the one or more processors, for inclusion in the small data environment, rows in the table comprising maximum and minimum values of the identified one or more fields excluding the outlier values;
• and
• selecting, by the one or more processors, for inclusion in the small data environment, rows in the table comprising average values for an interval of values of the identified one or more fields in the table;
• and
• generating, by the one or more processors, the small data environment, the small data environment comprising the portion of each table.

A computer program product for improving performance of queries with historically low performance in a big data environment, the computer program product comprising:

• one or more computer readable storage media and program instructions collectively stored on the one or more computer readable storage media readable by at least one processing circuit to:
• identify a query with low performance;
• generate a small data environment from the big data environment, the small data environment for use in optimizing the query with low performance, the generating comprising:
• automatically identify one or more tables and one or more fields for inclusion in the small data environment, wherein each of the identified one or more tables and each of the one or more fields is referenced in the query with the low performance;
• sample a portion of each table of the identified one or more tables such that each table in the small data environment comprises common data traits to a whole of each table, the sampling comprising:
• for each table for each table of the identified one or more tables:
• select, for inclusion in the small data environment, rows in the table comprising fields with outlier values for each of the identified one or more fields;
• select, for inclusion in the small data environment, rows in the table comprising maximum and minimum values of the identified one or more fields excluding the outlier values;
• and
• select, for inclusion in the small data environment, rows in the table comprising average values for an interval of values of the identified one or more fields in the table;
• generate the small data environment, the small data environment comprising the portion of each table;
• and
• performance test an optimized version of the query with low performance, by executing the optimized version on the small data environment.