[Interpretation of the DataNode source code for loading Schema in Mycat1.6]

1. Interpretation of the DataNode source code for loading Schema in Mycat1.6

//<dataNode name="dn1" dataHost="localhost1_gaojingsong1" database="scott" />
private void load(String dtdFile, String xmlFile) {
	InputStream dtd = null;
	InputStream xml = null;
		 
	dtd = XMLSchemaLoader.class.getResourceAsStream(dtdFile);
	xml = XMLSchemaLoader.class.getResourceAsStream(xmlFile);
	Element root = ConfigUtil.getDocument(dtd, xml).getDocumentElement();
	//Load all DataHost first
	loadDataHosts(root);
	//Reload all DataNodes
	 loadDataNodes(root);
	//Finally load all schemas
	loadSchemas(root);
		 
}
//<dataNode name="dn1" dataHost="localhost1_gaojingsong1" database="scott" />
private void loadDataNodes(Element root) {
    //Read the DataNode branch
    NodeList list = root.getElementsByTagName("dataNode");
	for (int i = 0, n = list.getLength(); i < n; i++) {
		Element element = (Element) list.item(i);
		String dnNamePre = element.getAttribute("name");

		String databaseStr = element.getAttribute("database");
		String host = element.getAttribute("dataHost");
		// string is not empty
		if (empty(dnNamePre) || empty(databaseStr) || empty(host)) {
			throw new ConfigException("dataNode " + dnNamePre + " define error
,attribute can't be empty");
		}
		//dnNames (name), databases (database), hostStrings (dataHost) can be configured with multiple
, separated by ',', '$', '-',
		//But you need to ensure the number of databases * the number of dataHosts = the number of names
		//If multiple dataHost and multiple databases are written in one tag, each dataHost owns all databases
		//E.g:
		//Then: localhost1 has dn1$0-75, localhost2 also has dn1$0-75 (corresponding to db$76-151)
	String[] dnNames = io.mycat.util.SplitUtil.split(dnNamePre, ',', '$', '-'); 
	String[] databases = io.mycat.util.SplitUtil.split(databaseStr, ',' , '$', '-');
	 String[] hostStrings = io.mycat.util.SplitUtil.split(host, ',', '$', '-'); 
      //Please see the complex configuration relationship here Step 2 Experimental results to understand  
		if (dnNames.length > 1 && dnNames.length != databases.length * hostStrings.length) {
			throw new ConfigException("dataNode " + dnNamePre
							+ " define error ,dnNames.length must be=databases.length*hostStrings.length");
		}
		if (dnNames.length > 1) {
			
			List<String[]> mhdList = mergerHostDatabase(hostStrings, databases);
			for (int k = 0; k < dnNames.length; k++) {
				String[] hd = mhdList.get(k);
				String dnName = dnNames[k];
				String databaseName = hd[1];
				String hostName = hd[0];
				createDataNode(dnName, databaseName, hostName);
			}

		} else {
			createDataNode(dnNamePre, databaseStr, host);
		}

	}
}

/**
	 * Match DataHost and Database, each DataHost has each Database name
	 * @param hostStrings
	 * @param databases
     * @return
     */
private List<String[]> mergerHostDatabase(String[] hostStrings,	String[] databases) {
	List<String[]> mhdList = new ArrayList<>();
	for (int i = 0; i < hostStrings.length; i++) {
		String hostString = hostStrings[i];
		for (int i1 = 0; i1 < databases.length; i1++) {
			String database = databases[i1];
			String[] hd = new String[2];
			hd[0] = hostString;
			hd[1] = database;
			mhdList.add(hd);
		}
	}
	return mhdList;
}

private void createDataNode(String dnName, String database, String host) {
	DataNodeConfig conf = new DataNodeConfig(dnName, database, host);		
	if (dataNodes.containsKey(conf.getName())) {
		throw new ConfigException("dataNode " + conf.getName() + " duplicated!");
	}
	
	if (!dataHosts.containsKey(host)) {
		throw new ConfigException("dataNode " + dnName + " reference dataHost:" + host + " not exists!");
	}

	dataHosts.get(host).addDataNode(conf.getName());
	dataNodes.put(conf.getName(), conf);
}

public final class DataNodeConfig {
	private final String name;
	private final String database;
	private final String dataHost;
}

2. Validation of experimental results

 

 in conclusion:

<dataNode name="dn1$0-75" dataHost="localhost$1-10" database="db$0-759" />

         name.length must be=databases.length*dataHost.length"

//There is no direct path from A to C, and it needs to transit through B. It is known that there are three databases from A to B, and two dataHost roads from B to C.

//, how about there are several options from A to C