Cassandra Database Migration and Expansion
1. First, download the Cassandra tar.gz package. I installed version 3.9 of Cassandra. The download address is http://archive.apache.org/dist/cassandra/3.9/apache-cassandra-3.9-bin.tar.gz.
2. After downloading, extract the file using the command:
`tar zxvf apache-cassandra-3.9-bin.tar.gz`
3. Configuration
Navigate to the extracted Cassandra directory and modify the directories for datafile, commitlog, and saved_caches in the `conf/cassandra.yaml` file. The default paths are: `$CASSANDRA_HOME/data/data`, `$CASSANDRA_HOME/data/commitlog`, and `$CASSANDRA_HOME/data/saved_caches`. You can adjust these based on your needs.
I set the following paths: `/var/lib/cassandra/data`, `/var/lib/cassandra/commitlog`, and `/var/lib/cassandra/saved_caches`.
Create these directories and change their ownership to a regular user:
```bash
sudo mkdir /var/lib/cassandra/data
sudo mkdir /var/lib/cassandra/commitlog
sudo mkdir /var/lib/cassandra/saved_caches
sudo chown -R ly:ly /var/lib/cassandra/data
sudo chown -R ly:ly /var/lib/cassandra/commitlog
sudo chown -R ly:ly /var/lib/cassandra/saved_caches
```
If you need to configure Cassandra memory, edit the `cassandra-env.sh` file under the `conf` directory. Set `MAX_HEAP_SIZE` for maximum memory and `HEAP_NEW_SIZE` for initial memory. Both parameters should be set together; otherwise, Cassandra might fail to start.
4. Running Cassandra
Once everything is configured, start Cassandra by running:
```bash
bin/cassandra
```
Wait for the process to initialize. Then check the process with:
```bash
ps -aux | grep cassandra
```
When a process like `5012` appears, Cassandra has started successfully.
5. Start CQL
Use the following command to launch the CQL shell:
```bash
bin/cqlsh
```
This allows you to interact with the database using CQL statements. Ensure Python 2.7 or higher is installed, as it's required to run cqlsh.
6. Stop Cassandra
To stop Cassandra, use the kill command:
```bash
kill 5012
```
7. Test
Write a simple Java program to insert data into Cassandra. You can refer to tutorials such as [JDBC connection method](http://ju.outofmemory.cn/entry/210437) or [Cassandra.Client method](http://blog.csdn.net/maosijunzi/article/details/42268061).
During runtime, you may encounter an error like:
`java.lang.ClassNotFoundException: com.google.common.util.concurrent.AsyncFunction`
This usually indicates missing dependencies. Make sure the following JAR files are included:
- `cassandra-driver-core-*.jar`
- `guava-*.jar`
- `metrics-core-*.jar`
- `netty-all-*.jar`
- `slf4j-api-*.jar`
**Cassandra Database Migration (Two Methods)**
The first method: Copy Command
This method is suitable when the amount of data is small.
Use the following command to export a table:
```sql
COPY mykeyspace.mytable TO '/home/db.csv';
```
Then, in another cluster, create the same table structure and import the data using:
```sql
COPY app12345.mytable FROM '/home/db.csv';
```
However, this approach is not efficient for large datasets, as it can take a long time and result in large files.
The second method: sstableloader Tool
The `sstableloader` tool is located in the `bin` directory of Cassandra. It is used to import SSTable files from one cluster to another.
Suppose your table is `mykeyspace.mytable`, and the data is stored in directories `/disk/data1` and `/disk/data2` across multiple nodes.
First, create the same keyspace and table structure in the new cluster. Then, execute the following commands on each node of the old cluster:
```bash
bin/sstableloader -d IP -u cassandra -pw cassandra -t 100 /disk/data1/mykeyspace/mytable
bin/sstableloader -d IP -u cassandra -pw cassandra -t 100 /disk/data2/mykeyspace/mytable
```
Here, `-d` specifies the target cluster IP, `-u` and `-pw` are the username and password, and `-t` sets the traffic limit (e.g., 100MB/s).
Once all nodes are processed, the data will be imported into the new cluster. You can also run multiple nodes concurrently if your system's IO and network allow it.
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