Csaba Ringhofer created IMPALA-8409:
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Summary: STRINGs without stats have too low row-size in explain
plan
Key: IMPALA-8409
URL: https://issues.apache.org/jira/browse/IMPALA-8409
Project: IMPALA
Issue Type: Bug
Components: Frontend
Affects Versions: Impala 3.2.0
Reporter: Csaba Ringhofer
STRING columns without avg_size statistic are calculated into the row-size as
11 bytes, while they take 12 bytes in the tuple (+ more somewhere in the
memory if they are not empty). The issue is caused by adding -1 (meaning
unknown) to the 12 byte slot size.
I think that this doesn't cause problems, as the estimation is probably way off
without statistics anyway, but row-size >= tuple size seems like a meaningful
invariant that we shouldn't break.
Reproduce:
{code}
create table test_row_size (s string);
explain select * from test_row_size;
Result:
...
WARNING: The following tables are missing relevant table and/or column
statistics.
default.test_row_size
...
00:SCAN HDFS [default.test_row_size]
partitions=1/1 files=0 size=0B
row-size=11B cardinality=0
{code}
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