docs: update usage and concurrency tuning guidance

Closes #6

Closes #8

Author: obrunsmann

README.md

@@ -12,6 +12,7 @@ This is a simple backup script for MySQL servers, designed to help you easily ba
 Before you can use this tool, make sure you have the following prerequisites installed on your system:
 
 - **MySQL Client**: Ensure that you have the MySQL client installed to interact with your MySQL databases.
+- **GNU Parallel**: Required to run backup jobs concurrently.
 
 ## Setup
 
@@ -33,21 +34,23 @@ Before you can use this tool, make sure you have the following prerequisites ins
    - `db_host`: The hostname or IP address of your MySQL server.
    - `db_user`: The MySQL user with backup privileges.
    - `db_pass`: The password for the MySQL user.
-   - `max_parallel`: The maximum number of parallel database backups.
+   - `max_parallel`: The maximum number of parallel database backups, or `auto`.
+   - `max_parallel_cap`: Upper bound when `max_parallel=auto`.
+   - `mysql_connection_reserve`: Number of MySQL connections reserved for non-backup traffic when `max_parallel=auto`.
    - `max_backups`: The maximum number of backup sets to retain.
 
 4. Make sure the script file is executable.
 
    ```bash
-   chmod +x backup.sh
+   chmod +x dump.sh
    ```
 
 ## Usage
 
-To create database backups using this tool, simply run the `backup.sh` script:
+To create database backups using this tool, simply run the `dump.sh` script:
 
 ```bash
-./backup.sh
+./dump.sh
 ```
 
 The script will perform the following actions:
@@ -60,12 +63,36 @@ The script will perform the following actions:
 
 4. **Cleanup Old Backups**: It checks the number of backup sets and removes old backups if the number exceeds the `max_backups` setting.
 
+## Concurrency Tuning
+
+For large MySQL servers (for example 400+ databases), set:
+
+```bash
+max_parallel=auto
+max_parallel_cap=16
+mysql_connection_reserve=20
+```
+
+With `auto`, the script computes parallel jobs from:
+
+- detected CPU core count
+- MySQL `max_connections` minus `mysql_connection_reserve`
+- `max_parallel_cap`
+
+The minimum of these values is used as job count.
+
+Guidelines:
+
+- Many small databases: increase `max_parallel_cap` carefully and observe DB load.
+- Few large databases: lower cap can reduce I/O contention and stabilize runtime.
+- Busy production DB: increase `mysql_connection_reserve` to protect foreground traffic.
+
 ## Example
 
 Here's an example of how to run the backup script:
 
 ```bash
-./backup.sh
+./dump.sh
 ```
 
 ## License
@@ -78,4 +105,4 @@ This backup tool is released under the MIT License. See the [LICENSE](LICENSE) f
 
 ---
 
-That's it! You now have a simple backup tool to help you manage your MySQL database backups. If you encounter any issues or have suggestions for improvements, feel free to open an issue on GitHub or contribute to the project.
+That's it! You now have a simple backup tool to help you manage your MySQL database backups. If you encounter any issues or have suggestions for improvements, feel free to open an issue on GitHub or contribute to the project.