[DRILL-5105] Query time increases exponentially with increasing nested levels

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.9.0
• Component/s: Storage - JSON
• Labels: ready-to-commit

Environment

3 Node Cluster with default memory and configurations.

• Assignee: Chunhui Shi
• Reporter: Abhishek Girish
• Reviewer: Paul Rogers
• Created: 05/Dec/16 04:32
• Updated: 27/Mar/17 05:59
• Resolved: 14/Jan/17 01:53

Description

The time taken to query any JSON dataset depends on number of nested levels within the dataset. Also, increasing the complexity of the dataset further impacts the execution time.

Tabulated below is cached query execution times for a simple select * query over two simple forms of JSON datasets:

No. Levels	Time (s) Dataset 1	Time (s) Dataset 2
1	0.22	0.27
2	0.23	0.25
4	0.24	0.22
8	0.22	0.23
16	0.34	0.48
24	25.76	72.51
26	103.48	289.6
28	336.12	1151.94
30	1342.22	4586.79
32	5360.2	Expected: ~20k

The above table lists query times for 20 different JSON files, 10 belonging to dataset 1 & 10 belonging to dataset 2. Each have 1 record, but the number of nested levels within them vary as mentioned in the "No. Levels" column.

It appears that the query time almost doubles with addition of a nested level (note that in the table above, it translates to almost 4x across levels starting 24)

The below two are the representative datasets, showcasing simple JSON structures with nested levels.

Structure of Dataset 1:

{
  "level1": {
    "field1": "a",
    "level2": {
      "field1"": "b",
      ...
    }
  }
}

Structure of Dataset 2:

"{
  "level1": {
    "field1": ""a",
    "field2": {
      "nfield1": true,
      "nfield2": 1.1
    },
    "level2": {
      "field1": "b",
      "field2": {
        "nfield1": false,
        "nfield2": 2.2
      },
      ...
    }
  }
}

Issue Links

• links to: GitHub Pull Request #715