Common Operations of Alluxio

Preparations

Create a cluster with Alluxio installed.
Log in to the active Master node in a cluster as user root using the password set during cluster creation.
Run the following command to configure environment variables:
source /opt/client/bigdata_env

Using the Alluxio Shell

The Alluxio shell contains multiple command line operations that interact with Alluxio.

View a file system operation command list:
alluxio fs
Run the ls command to list the files in Alluxio. For example, list all files in the root directory:
alluxio fs ls /
Run the copyFromLocal command to copy local files to Alluxio:
alluxio fs copyFromLocal /home/test_input.txt /test_input.txt
Command output:
```
Copied file:///home/test_input.txt to /test_input.txt
```
Run the ls command again to list the files in Alluxio. The copied test_input.txt file is listed:
alluxio fs ls /
Command output:
```
12       PERSISTED 11-28-2019 17:10:17:449 100% /test_input.txt
```
The test_input.txt file is displayed in Alluxio. The parameters in the file indicate the file size, whether the file is persistent, creation date, cache ratio of the file in Alluxio, and file name.
Run the cat command to print file content:
alluxio fs cat /test_input.txt
Command output:
```
Test Alluxio
```

Mounting Function of Alluxio

Alluxio uses a unified namespace feature to unify the access to storage systems. For details, see https://docs.alluxio.io/os/user/2.0/en/advanced/Namespace-Management.html.

This feature allows users to mount different storage systems to an Alluxio namespace and seamlessly access files across storage systems through the Alluxio namespace.

Create a directory as a mount point in Alluxio.
alluxio fs mkdir /mnt
```
Successfully created directory /mnt
```
Mount an existing OBS file system to Alluxio. (Prerequisite: An agency with the OBS OperateAccess permission has been configured for the cluster. For details, see Configuring a Storage-Compute Decoupled Cluster (Agency).) The obs-mrstest file system is used as an example. Replace the file system name with the actual one.
alluxio fs mount /mnt/obs obs://obs-mrstest/data
```
Mounted obs://obs-mrstest/data at /mnt/obs
```
List files in the OBS file system using the Alluxio namespace. Run the ls command to list the files in the OBS mount directory.
alluxio fs ls /mnt/obs
```
38       PERSISTED 11-28-2019 17:42:54:554   0% /mnt/obs/hive_load.txt
12       PERSISTED 11-28-2019 17:43:07:743   0% /mnt/obs/test_input.txt
```
You can also view the newly mounted files and directories on the Alluxio web UI.

After the mounting is complete, you can seamlessly exchange data between different storage systems through the unified namespace of Alluxio. For example, run the ls -R command to list all files in a directory recursively:

alluxio fs ls -R /

        0       PERSISTED 11-28-2019 11:15:19:719  DIR /app-logs
        1       PERSISTED 11-28-2019 11:18:36:885  DIR /apps
        1       PERSISTED 11-28-2019 11:18:40:209  DIR /apps/templeton
239440292       PERSISTED 11-28-2019 11:18:40:209   0% /apps/templeton/hive.tar.gz
.....
        1       PERSISTED 11-28-2019 19:00:23:879  DIR /mnt
        2       PERSISTED 11-28-2019 19:00:23:879  DIR /mnt/obs
       38       PERSISTED 11-28-2019 17:42:54:554   0% /mnt/obs/hive_load.txt
       12       PERSISTED 11-28-2019 17:43:07:743   0% /mnt/obs/test_input.txt
.....

The command output shows all files that are from the mounted storage system in the root directory of the Alluxio file system (the default directory is the HDFS root directory, that is, hdfs://hacluster/). The /app-logs and /apps directories are in HDFS, and the /mnt/obs/ directory is in OBS.

Using Alluxio to Accelerate Data Access

Alluxio can accelerate data access, because it uses memory to store data. Example commands are provided as follows:

Upload the test_data.csv file (a sample that records recipes) to the /data directory of the obs-mrstest file system. Run the ls command to display the file status.
alluxio fs ls /mnt/obs/test_data.csv
```
294520189       PERSISTED 11-28-2019 19:38:55:000   0% /mnt/obs/test_data.csv
```
The output indicates that the cache percentage of the file in Alluxio is 0%, that is, the file is not in Alluxio memory.
Count the occurrence times of the word "milk" in the file, and calculate the time consumed.
time alluxio fs cat /mnt/obs/test_data.csv | grep -c milk
```
52180

real    0m10.765s
user    0m5.540s
sys     0m0.696s
```
Data is stored in memory after being read for the first time. When Alluxio reads data again, the data access speed is increased. For example, after running the cat command to obtain a file, run the ls command to check the file status.
alluxio fs ls /mnt/obs/test_data.csv
```
294520189       PERSISTED 11-28-2019 19:38:55:000 100% /mnt/obs/test_data.csv
```
The output shows that the file has been fully loaded to Alluxio.
Access the file again, count the occurrence times of the word "eggs", and calculate the time consumed.
time alluxio fs cat /mnt/obs/test_data.csv | grep -c eggs
```
59510

real    0m5.777s
user    0m5.992s
sys     0m0.592s
```
According to the comparison of the two time consumption records, the time consumed for accessing data stored in Alluxio memory is significantly reduced.