[TAJO-356] Improve TajoClient to directly get query results in the first request

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.8.0, 0.9.0
• Fix Version/s: 0.8.0, 0.9.0
• Component/s: Java Client
• Assignee: Hyunsik Choi
• Reporter: Hyunsik Choi
• Created: 02/Dec/13 18:34
• Updated: 08/Apr/14 12:44
• Resolved: 08/Apr/14 12:38

Description

Currently, TajoClient cannot deal with simple queries (e.g., select * from table limit 1 or select 1) which are executed in TajoMaster without distributed execution. The final results are always stored in HDFS, and TajoClient gets the result via scanner with TableDesc obtained from GetQueryResultResponse.

For simple queries directly executed at TajoMaster, TajoClient needs to directly get some binary serialized rows results from GetQueryStatusResponse or GetQueryResultResponse instead of reading materialized tables.

This feature would be also useful for low latency queries, EXPLAIN clauses and expr-only statements without FROM clause.

Issue Links

• is duplicated by: TAJO-234 Does not work without 'from clause'
• is related to: TAJO-404 Tajo does not recognize boolean literal