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Getting the Metadata Statistics of a HDFS file

 Below bash command will give you the metadata statistics such as distinct number of columns and   length of a record in a raw file. This will help you on landing phase, to determine if any raw files are corrupted.This will help you especially when there are n number of raw files are in your landing area and you need to do a quick testing of it. (The command is hard coded with .dat extension, please change according to your file type)

  1. Sample Out put of the below command is as follows:
    2. Output will be saved to a metadata file metadata_stat_<unixtimestamp>
    3. If we have more than one value for distinct_no_of_cols for a files, this means one or more records of your file is corrupted or there are some quoted strings in your records which contains delimiter itself as a value
    4. If your file is a fixed length files , distinct_no_lengths columns should have only one value per file. 

command:

metafilename=metadata_stat_$(date +%s%3N).txt;echo file_name\|distinct_no_cols\|distinct_no_lengths>$metafilename;for filename in `hadoop fs -ls /path/to/data/files/ | awk '{print $NF}' | grep .dat$ | tr '\n' ' '`; do echo $filename \|$(hadoop fs -cat $filename | awk -F "," '{print NF}'|sort|uniq|tr "\n" "," | sed 's/\(.*\),/\1 /') \|$(hadoop fs -cat $filename | awk '{print length($0)}'|sort|uniq|tr "\n" "," | sed 's/\(.*\),/\1 /') >> $metafilename;done

Note: If you have delimiters inside a quoted string (which is mentioned in 2nd point) , you can use below command 


metafilename=metadata_stat_$(date +%s%3N).txt;echo file_name\|distinct_no_cols\|distinct_no_lengths>$metafilename;for filename in `hadoop fs -ls /path/to/data/file/files | awk '{print $NF}' | grep .dat$ | tr '\n' ' '`; do echo $filename \|$(hadoop fs -cat $filename | awk -vFPAT='([^,]*)|("[^"]+")' -vOFS=, '{print NF}'|sort|uniq|tr "\n" "," | sed 's/\(.*\),/\1 /') \|$(hadoop fs -cat $filename | awk '{print length($0)}'|sort|uniq|tr "\n" "," | sed 's/\(.*\),/\1 /') >> $metafilename;done



Comments

  1. KathyMarch 31, 2021 at 1:57 AM

    Well written articles like yours renews my faith in today's writers. The article is very informative. Thanks for sharing such beautiful information.
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