The document provides a detailed guide on migrating Hive data from an old Hadoop cluster to a new one, outlining steps for exporting, copying, and importing data. It includes commands and scripts for creating tables, exporting data by partition, using the distcp command for copying, and finally importing the data to the new cluster. Key references for further information on Hive import/export practices are also provided.

1. HIVE Data Migration
NHN Comico Data Laboratory
Bopyo Hong
2015-11-05

2. Overview
1. Concept
2. Export Data
from Old Hadoop Cluster
3. Data Copy
from Old Hadoop Cluster to New one
4. Import Data
to New Hadoop Cluster
5. Reference sites

3. Concept
Migration of Hive data from old hadoop cluster to new one
Hive
(old version)
Hive
(new version)

4. Export Data from Old Hadoop Cluster - 1
1. To make table list of database you want to export
Hive doesn’t support to export/import by DB unit
$ hive --database test -e 'SHOW TABLES' | sed -e '1d' > table_list.txt
2. To make export statements that is executed by partition
when you export whole table(not use partition), if the table is very big the export will
take too long time. So I recommend use partition.
In this example, export 2015-10-01 ~ 2014-10-31 partition
ex) partition name is dt
/user/hive/warehouse/test.db/tablename/dt=2015-10-01
/user/hive/warehouse/test.db/tablename/dt=2015-10-02
/user/hive/warehouse/test.db/tablename/dt=2015-10-03
……………………………………..
/user/hive/warehouse/test.db/tablename/dt=2015-10-31
$ source make_cmd_export_by_partition.sh 20151001 20151101 > export_201510.q

5. Export Data from Old Hadoop Cluster - 2
$vi make_cmd_export_by_partition.sh
#!/bin/bash
startdate=$1
enddate=$2
rundate="$startdate"
until [ "$rundate" == "$enddate" ]
do
YEAR=${rundate:0:4}
MONTH=${rundate:4:2}
DAY=${rundate:6:2}
DATE2=${YEAR}'-'${MONTH}'-'${DAY}
TBLS=(`cat table_list.txt`)
for TBL in ${TBLS[@]}
do
echo "export table ${TBL} PARTITION (dt='$DATE2') to '/user/hadoop/temp_export_dir/${TBL}/dt=$DATE2';"
echo
done
rundate=`date --date="$rundate +1 day" +%Y%m%d`
done

6. Export Data from Old Hadoop Cluster - 3
3. Export of test DB
$ source export_by_hive.sh export_201510.q
$vi export_by_hive.sh
#!/bin/bash
echo "export start `date +'%Y-%m-%d %H:%M'`“
# all tables couldn’t have same partitions, so need a option (-hiveconf hive.cli.errors.ignore=true)
hive -hiveconf hive.cli.errors.ignore=true --database test -f $1
echo "export end `date +'%Y-%m-%d %H:%M'`"

7. Data Copy from old hadoop cluster to new one
Data copy by using distcp command
You should execute distcp command on new hadoop cluster
old cluster url -> hftp://namenode_hostname:50070
new cluster url -> hdfs://namenode_hostname:8020
$ source distcp_script.sh
$ vi distcp_script.sh
#!/bin/bash
echo "`date +'%Y-%m-%d %H:%M'` distcp start“
# -pb option is necessary to avoid errors that could happen by difference of block size between old and new cluster
hadoop distcp -pb hftp://old_host:50070/user/hadoop/temp_export_dir hdfs://new_host:8020/user/bopyo.hong/temp_import_dir
echo "`date +'%Y-%m-%d %H:%M'` distcp end“

8. Import Data to New Hadoop Cluster - 1
1. To make import statement that is executed by partition
$ source make_cmd_import_by_partition.sh 20151001 20151101 > import_201510.q
$ vi make_cmd_import_by_partition.sh
#!/bin/bash
TBLS=(`cat table_list.txt`)
startdate=$1
enddate=$2
rundate="$startdate"
until [ "$rundate" == "$enddate" ]
do
YEAR=${rundate:0:4}
MONTH=${rundate:4:2}
DAY=${rundate:6:2}
DATE2=${YEAR}'-'${MONTH}'-'${DAY}
for TBL in ${TBLS[@]}
do
echo "import table ${TBL} PARTITION (dt='$DATE2') from '/user/bopyo.hong/temp_import_dir/${TBL}/dt=$DATE2';"
echo
done
rundate=`date --date="$rundate +1 day" +%Y%m%d`
done

9. Import Data to New Hadoop Cluster - 2
2. Import tables of test DB
$ source import_by_hiveql.sh import_201510.q
$ vi import_by_hiveql.sh
#!/bin/bash
echo "import start `date +'%Y-%m-%d %H:%M'`“
# all tables couldn’t have same partitions so need a option (-hiveconf hive.cli.errors.ignore=true)
hive -hiveconf hive.cli.errors.ignore=true --database test -f $1
echo "export start `date +'%Y-%m-%d %H:%M'`"

10. Reference site
https://cwiki.apache.org/confluence/display/Hive/LanguageManual+ImportExport
http://kickstarthadoop.blogspot.jp/2012/08/how-to-migrate-hive-table-from-one-hive.html
https://hadoop.apache.org/docs/r2.7.1/hadoop-distcp/DistCp.html#Command_Line_Options