[IMPALA-4173] Stats computation on fixed length char columns still tries to compute Max & Avg column length

• Type: Bug
• Status: Resolved
• Priority: Minor
• Resolution: Won't Fix
• Affects Version/s: Impala 2.5.0
• Component/s: Frontend
• Labels: ramp-up statistics
• Target Version: Impala 2.8.0
• Assignee: Unassigned
• Reporter: Mostafa Mokhtar
• Created: 21/Sep/16 05:33
• Updated: 19/Jan/17 22:51
• Resolved: 19/Jan/17 22:51

Description

For fixed length char column the query issued to compute the statistics tried to calculate Max and Average column length which is already known from the column data type.

Query issued

SELECT NDV(l_orderkey) AS l_orderkey, CAST(-1 as BIGINT), MAX(length(l_orderkey)), AVG(length(l_orderkey)) FROM tpch_3000_parquet.l_orderkey_char_11

Table schema

describe  tpch_3000_parquet.l_orderkey_char_11;
+------------+----------+---------+
| name       | type     | comment |
+------------+----------+---------+
| l_orderkey | char(11) |         |
+------------+----------+---------+

Table statistics, not clean why the Avg size is not 11, I guess an overflow might be happening somewhere as row count is 18 Billion.

+------------+----------+------------------+--------+----------+-------------------+
| Column     | Type     | #Distinct Values | #Nulls | Max Size | Avg Size          |
+------------+----------+------------------+--------+----------+-------------------+
| l_orderkey | CHAR(11) | 4525097984       | -1     | 11       | 10.38269996643066 |
+------------+----------+------------------+--------+----------+-------------------+