[IMPALA-4257] Parallel Queries fired from Cognos get stuck forever.

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Cannot Reproduce
• Affects Version/s: Impala 2.5.0
• Component/s: Clients
• Labels: performance
• Environment: Dev
• Target Version: Product Backlog
• Assignee: Unassigned
• Reporter: Deepak Nagar
• Created: 07/Oct/16 16:50
• Updated: 07/Mar/18 17:15
• Resolved: 07/Mar/18 17:15

Description

We are using cloudera Impala 2.5.0 and created Parquet table (snappy compression). These tables are being accessed by Cognos 10.2 version for generating the reports and cognos 10.2 runs the queries in Dynamic Query Mode (Dynamic Query Mode introduces the concept of a memory-resident data cache in cognos. The query engine ultimately issue SQL code against the database in order to populate the cache, only minimal and simplified queries are issued against the database). These simplified queries are however fired to Impala in parallel.

The parallel execution of these queries seems to slowing down the whole process and most of the queries (6 out of 8 fired in parallel in our case) never finish, they run for days. The same set of queries when run individually in sequence take only few seonds to complete.