Run Compaction on Hive Tables

You must use the Hive pre-upgrade tool JAR you downloaded to run compaction on Hive tables. The pre-upgrade tool looks for files in an ACID table that contains update or delete events, and generates scripts to compact these tables. You can run the pre-upgrade tool command on the command line before or after upgrading Ambari. You do not actually use Ambari to run this command.

Some transactional tables in HDP 2.6.5.x require a major compaction before upgrading the tables to Hive 3.0 in Cloudera Private Cloud Base. Running the Hive pre-upgrade tool identifies the tables that need such a compaction and provides scripts that you run to perform the compaction. Depending on the number of tables and partitions, and the amount of data involved, compactions might take a significant amount of time and resources. The script output of the pre-upgrade tool includes some heuristics that might help estimate the time required. If no script output is produced, no compaction is needed.

Log in as the hive user.
```
$ sudo su - hive
```
Export the JAVA_HOME environment variable if necessary.
```
$ export JAVA_HOME=[ path to your installed JDK ]
```

Set STACK_VERSION to the HDP version you are running.

$ export STACK_VERSION=`hdp-select status hive-server2 | awk '{ print $3;
}'`

Run the pre-upgrade tool command.

$ $JAVA_HOME/bin/java -cp /usr/hdp/$STACK_VERSION/hive/lib/derby-10.10.2.0.jar:/usr/hdp/$STACK_VERSION/hive/lib/*:/usr/hdp/$STACK_VERSION/hadoop/*:/usr/hdp/$STACK_VERSION/hadoop/lib/*:/usr/hdp/$STACK_VERSION/hadoop-mapreduce/*:/usr/hdp/$STACK_VERSION/hadoop-mapreduce/lib/*:/usr/hdp/$STACK_VERSION/hadoop-hdfs/*:/usr/hdp/$STACK_VERSION/hadoop-hdfs/lib/*:/usr/hdp/$STACK_VERSION/hadoop/etc/hadoop/*:/tmp/hive-pre-upgrade-3.1.0.3.1.0.258-3.jar:/usr/hdp/$STACK_VERSION/hive/conf/conf.server:/etc/hadoop/conf/:/etc/hive/conf/ org.apache.hadoop.hive.upgrade.acid.PreUpgradeTool > {hive_log_dir}/pre_upgrade_{target_version}.log

The output indicates whether you need to perform compaction or not. In the /tmp directory, scripts named compacts_nnnnnnnnnnnnn.sql appear that contain ALTER statements for compacting tables.

ALTER TABLE default.t COMPACT 'major';
- Generated total of 1 compaction commands
- The total volume of data to be compacted is 0.001155MB

From the volume of data to be compacted, you can gauge how long the actual upgrade might take. If no scripts appear, a message in the output says you do not need to compact tables:

... org.apache.hadoop.hive.upgrade.acid.PreUpgradeTool - No compaction
                       is necessary

Check the logs on the Hive Metastore host for any errors.
- {hive_log_dir}/pre_upgrade_{target_version}.log
- /tmp/hive/hive.log
If there are no errors, proceed; otherwise, resolve the errors, and repeat this procedure.
On the node where the Hive Metastore resides, log in as a user who has privileges to alter the Hive database.

Start Beeline as the Hive service user.

$ beeline -u 'jdbc:hive2://<Metastore host name>:10000' -n hive

On the Hive command line run the compaction script.
```
hive> !run /tmp/compacts_nnnnnnnnnnnnn.sql
```
Output confirms that compaction is queued:
```
INFO : Compaction enqueued with id 3
...
```

Run Compaction on Hive Tables

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