[GitHub] [druid] nishantmonu51 opened a new issue #10560: Datasources tab generates a query which can cause ArithmeticException divide by zero

[GitBox]

nishantmonu51 opened a new issue #10560:
URL: https://github.com/apache/druid/issues/10560


   ### Description
   Noticed this on the datasources tab in druid management console. 
   Datasources tab was not showing any data since the underlying SQL was 
running into java.lang.ArithmeticException divide by zero. 
   
   <img width="1483" alt="Screen Shot 2020-11-06 at 12 25 34 AM" 
src="https://user-images.githubusercontent.com/5023786/98284502-3a2e5500-1fc7-11eb-8d9a-c714f31922fd.png";>
   
   Here is the query generated by the view - 
   ```
   SELECT
   datasource,
   COUNT(*) FILTER (WHERE (is_published = 1 AND is_overshadowed = 0) OR 
is_realtime = 1) AS num_segments,
   COUNT(*) FILTER (WHERE is_available = 1 AND ((is_published = 1 AND 
is_overshadowed = 0) OR is_realtime = 1)) AS num_available_segments,
   COUNT(*) FILTER (WHERE is_published = 1 AND is_overshadowed = 0 AND 
is_available = 0) AS num_segments_to_load,
   COUNT(*) FILTER (WHERE is_available = 1 AND NOT ((is_published = 1 AND 
is_overshadowed = 0) OR is_realtime = 1)) AS num_segments_to_drop,
   SUM("size") FILTER (WHERE (is_published = 1 AND is_overshadowed = 0) OR 
is_realtime = 1) AS total_data_size,
   SUM("size" * "num_replicas") FILTER (WHERE (is_published = 1 AND 
is_overshadowed = 0) OR is_realtime = 1) AS replicated_size,
   MIN("size") FILTER (WHERE (is_published = 1 AND is_overshadowed = 0) OR 
is_realtime = 1) AS min_segment_size,
   (SUM("size") FILTER (WHERE (is_published = 1 AND is_overshadowed = 0) OR 
is_realtime = 1) / COUNT(*) FILTER (WHERE (is_published = 1 AND is_overshadowed 
= 0) OR is_realtime = 1)) AS avg_segment_size,
   MAX("size") FILTER (WHERE (is_published = 1 AND is_overshadowed = 0) OR 
is_realtime = 1) AS max_segment_size,
   SUM("num_rows") FILTER (WHERE (is_published = 1 AND is_overshadowed = 0) OR 
is_realtime = 1) AS total_rows,
   (SUM("size") FILTER (WHERE (is_published = 1 AND is_overshadowed = 0) OR 
is_realtime = 1) / SUM("num_rows") FILTER (WHERE (is_published = 1 AND 
is_overshadowed = 0) OR is_realtime = 1)) AS avg_row_size
   FROM sys.segments
   GROUP BY 1
   ```
   Below snapshot showing total_rows reported by druid as 0 that causes the 
calculation of avg_row_size to break
   
   <img width="1457" alt="Screen Shot 2020-11-06 at 12 38 13 AM" 
src="https://user-images.githubusercontent.com/5023786/98285311-64344700-1fc8-11eb-9aec-50d68b96f428.png";>
   
   multiple issues here which could be improved - 
   
   1. Improve the UI so that the generated SQL query do not run into divide by 
zero issue
   2. Figure out why druid is returning num_rows as zero
   


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