Validating HFiles

Before migrating to COD CDP Public Cloud ensure that your HFiles are compatible with the version Apache HBase in CDP.

After converting all the PREFIX_TREE encoded HFiles to a supported format, there may be HFiles that are not compatible with HBase in CDP.

Use the following pre-upgrade commands to validate HFiles:

```
hbase pre-upgrade validate-hfile
```
```
hbase hbck
```

The validate-hfile tool lists all the corrupt HFiles with details. The hbck command identifes HFiles that are in a bad state.

If your cluster is Kerberized, ensure that you run the kinit command as a hbase user before running the pre-upgrade commands.

Download and distribute parcels for the target version of CDP.
important
Do not activate the parcel yet.
If the downloaded parcel version is higher than the current Cloudera Manager version, the following error message displayed:
Error for parcel CDH-7.x.parcel : Parcel version 7.X is not supported by this version of Cloudera Manager. Upgrade Cloudera Manager to at least 7.X before using this version of the parcel.
You can safely ignore this error message.
Find the installed parcel at /opt/cloudera/parcels.
For example: /opt/cloudera/parcels/CDH-7.1.1-1.cdh7.1.1.p0.3224867/bin/hbase

Use the CDP parcel to run the pre-upgrade commands. Cloudera recommends that you run them on an HMaster host.

Run the hbase pre-upgrade validate-hfile command using the new CDP installation.
This command checks every HFile (including snapshots) to ensure that the HFiles are not corrupted and have the compatible block encoding. It opens every HFile, and this operation can take a long time based on the size and number of HFiles in your cluster.
For example, if you have installed the CDH-7.1.1-1 parcel, you must run the following command:
```
/opt/cloudera/parcels/CDH-7.1.1-1.cdh7.1.1.p0.3224867/bin/hbase pre-upgrade validate-hfile
```
If there are no incompatible HFiles, the following message is displayed:
```
Checked 3 HFiles, none of them are corrupted.
                        There are no incompatible HFiles.
```
If you have an incompatible HFile, a similar error message to this is displayed:
```
2018-06-05 16:20:47,322 INFO  [main] tool.HFileContentValidator: Corrupted file: hdfs://example.com:8020/hbase/data/default/t/72ea7f7d625ee30f959897d1a3e2c350/prefix/7e6b3d73263c4851bf2b8590a9b3791e
                        2018-06-05 16:20:47,383 INFO  [main] tool.HFileContentValidator: Corrupted file: hdfs://example.com:8020/hbase/archive/data/default/t/56be41796340b757eb7fff1eb5e2a905/f/29c641ae91c34fc3bee881f45436b6d1
                    
```
If you get an error message, continue with Step 2 otherwise skip to Step 5.
Identify what kind of HFiles were reported in the error message.
The report can contain two different kinds of HFiles, they differ in their path:
- If an HFile is in /hbase/data then it belongs to a table.
- If an HFile is located under /hbase/archive/data then it belongs to a snapshot.
Fix the HFiles that belong to a table.
1. Get the table name from the output.
  Our example output showed the /hbase/data/default/t/… path, which means that the HFile belongs to the t table which is in the default namespace.
2. Rewrite the HFiles by issuing a major compaction. Use the old installation.
  shell> major_compact 't'
  
  When compaction is finished, the invalid HFile disappears.

Fix the HFiles that belong to a snapshot that is needed. Use the old installation.

Find the snapshot which refers the invalid HFile. You can do this using a shell script and the following example code. In our example output, the HFile is 29c641ae91c34fc3bee881f45436b6d1:

#!/bin/bash
                                # Find the snapshot which referes to the invalid HFile
                                for snapshot in $(hbase snapshotinfo -list-snapshots 2> /dev/null | cut -f 1 -d \|); 
                                do
                                echo "checking snapshot named '${snapshot}'"
                                hbase snapshotinfo -snapshot "${snapshot}" -files 2> /dev/null | grep 29c641ae91c34fc3bee881f45436b6d1
                                done

The following output means that the invalid file belongs to the t_snap snapshot:

checking snapshot names 't__snap'
                                    1.0 K t/56be41796340b757eb7fff1eb5e2a905/f/29c641ae91c34fc3bee881f45436b6d1 (archive)

Convert snapshot to another HFile format if data encoding is the issue using the following command:

# creating a new namespace for the cleanup process
                                hbase> create_namespace 'pre_upgrade_cleanup'
                                # creating a new snapshot
                                hbase> clone_snapshot 't_snap', 'pre_upgrade_cleanup:t'
                                hbase> alter 'pre_upgrade_cleanup:t', { NAME => 'f', DATA_BLOCK_ENCODING => 'FAST_DIFF' }
                                hbase> major_compact 'pre_upgrade_cleanup:t'

# removing the invalid snapshot
                                hbase> delete_snapshot 't_snap'
                                # creating a new snapshot
                                hbase> snapshot 'pre_upgrade_cleanup:t', 't_snap'
                                # removing temporary table
                                hbase> disable 'pre_upgrade_cleanup:t'
                                hbase> drop 'pre_upgrade_cleanup:t'
                                hbase> drop_namespace 'pre_upgrade_cleanup'

Run the hbck command on to identify HFiles in a bad state and remedy those HFiles.