Mikko Kivistö created HIVE-20574:
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Summary: Column statistics give erraneous numDistinct
Key: HIVE-20574
URL: https://issues.apache.org/jira/browse/HIVE-20574
Project: Hive
Issue Type: Bug
Components: Metastore, Statistics
Affects Versions: 2.3.2
Environment: Amazon EMR (BigTop based) from emr-5.9.0 to emr-5.16.0.
Reporter: Mikko Kivistö
1) Download the parquet file to s3/hdfs (e.g. hdfs:///tmp/testi_parquet/) using
some tool (aws cli, hdfs command or anything)
- S3: s3://www.smartdatahub.io/data/test.parquet
- HTTP: [http://www.smartdatahub.io/data/test.parquet]
- or the attachmen
eg. with aws cli, wget/curl/distcp can also be used
{{ aws s3 cp s3://www.smartdatahub.io/data/test.parquet .}}
{{hdfs dfs -mkdir hdfs:///tmp/testi_parquet/}}{{hdfs dfs -put test.parquet }}
{{hdfs:///tmp/testi_parquet/test.parquet}}
2) Create table default.testi_parquet2 on top of that using the schema provided
{{ CREATE TABLE `default.testi_parquet2`(}}
{{ `rakennustu` int, }}
{{ `kohdenimi` string, }}
{{ `tekstisuun` int, }}
{{ `tekstikoko` float, }}
{{ `tekstifont` string, }}
{{ `buix_bid` int, }}
{{ `paivitetty` string, }}
{{ `datanomist` string, }}
{{ `geom_geojson` string, }}
{{ `geom` binary, }}
{{ `extractdate` string)}}
{{ ROW FORMAT SERDE }}
{{ 'org.apache.hadoop.hive.ql.io.parquet.serde.ParquetHiveSerDe' }}
{{ STORED AS INPUTFORMAT }}
{{ 'org.apache.hadoop.hive.ql.io.parquet.MapredParquetInputFormat' }}
{{ OUTPUTFORMAT }}
{{ 'org.apache.hadoop.hive.ql.io.parquet.MapredParquetOutputFormat'}}
{{ LOCATION}}
{{ 'hdfs:///tmp/testi_parquet/';}}
{{ -- CHANGE THE LOCATION TO THE PREFIX/DIRECTORY YOU DOWNLOADED THE FILE FROM
STEP 1 IF IT DIFFERS FROM THE EXAMPLE}}
3) To collect the values showing you the actual reality of the data: Query the
distinct count, min and max of column "tekstisuun"
{{SELECT COUNT(DISTINCT tekstisuun), MAX(tekstisuun), MIN(tekstisuun) FROM
default.testi_parquet2; }}
and note them (min 0, max 0, distinct 1)
4) Compute statistics for the table using
{{ANALYZE TABLE default.testi_parquet2 COMPUTE STATISTICS FOR COLUMNS;}}
5) See erroneous statistics entry for numDistincts: Query the statistics by
using "
{{DESCRIBE FORMATTED default.testi_parquet2 tekstisuun}}
" and note the ERRANEOUS numDistincts value: 2
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