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/.
2. After downloading, extract the file. Use the command: `tar zxvf apache-cassandra-3.9-bin.tar.gz`.
3. Configuration
Navigate to the unzipped Cassandra directory and modify the `cassandra.yaml` file located in the `conf` folder. The default directories for data files, commit logs, and saved caches are `$CASSANDRA_HOME/data/data`, `$CASSANDRA_HOME/data/commitlog`, and `$CASSANDRA_HOME/data/saved_caches`. Adjust these paths based on your system's requirements.
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. For example:
```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 adjust memory settings, edit the `cassandra-env.sh` file under the `conf` directory. Set `MAX_HEAP_SIZE` for maximum heap size and `HEAP_NEW_SIZE` for initial heap size. Ensure both are set together; otherwise, Cassandra may fail to start.
4. Running Cassandra
Once all configurations are complete, start Cassandra by running the following command from the Cassandra directory:
```bash
bin/cassandra
```
Wait a few moments, then check the process using:
```bash
ps -aux | grep cassandra
```
When a process like `5012` appears, it means Cassandra has started successfully.
5. Start CQL
To access the Cassandra Query Language (CQL), run:
```bash
bin/cqlsh
```
This opens the CQL shell, where you can execute CQL commands to interact with the database. Note that this requires Python 2.7 or higher to be installed. If not available, the CQL shell will not launch.
6. Stop Cassandra
To stop Cassandra, use the `kill` command with the process ID:
```bash
kill 5012
```
7. Testing
You can test Cassandra by writing a simple Java program to insert data into the database. You can refer to tutorials such as [this one](http://ju.outofmemory.cn/entry/210437) for JDBC connection methods, or [this one](http://blog.csdn.net/maosijunzi/article/details/42268061) for using `Cassandra.Client`.
During runtime, you might 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 in your project:
- `cassandra-driver-core-*.jar`
- `guava-*.jar`
- `metrics-core-*.jar`
- `netty-all-*.jar`
- `slf4j-api-*.jar`
**Cassandra Database Migration (Two Methods)**
**Method 1: Using the Copy Command**
This method is suitable for small amounts of data. To export a table, use:
```sql
COPY mykeyspace.mytable TO '/home/db.csv';
```
This exports the `mytable` table to a CSV file named `db.csv`. Then, in the new cluster, create the same table structure and import the data using:
```sql
COPY app12345.mytable FROM '/home/db.csv';
```
However, this method is not efficient for large datasets, as it can take a long time and result in very large files.
**Method 2: Using the SSTableLoader Tool**
The `sstableloader` tool, found in the `bin` directory of Cassandra, is designed for importing SSTable files into a new cluster. Suppose your table is `mykeyspace.mytable`, and your data is stored in `/disk/data1` and `/disk/data2` on a 10-node cluster.
First, create the same keyspace and table structure in the new cluster. Then, run the following command 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's IP address, `-u` is the username, `-pw` is the password, and `-t` sets the traffic limit to 100 MB/s. Once all nodes have been processed, the data will be imported into the new cluster. If your system allows, you can run multiple nodes in parallel for faster migration.
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