聊聊canal的Position

序

本文主要研究一下canal的Position

Position

canal-1.1.4/protocol/src/main/java/com/alibaba/otter/canal/protocol/position/Position.java

public abstract class Position implements Serializable {

    private static final long serialVersionUID = 2332798099928474975L;

    public String toString() {
        return ToStringBuilder.reflectionToString(this, CanalToStringStyle.DEFAULT_STYLE);
    }

}

• Position定义了toString方法，使用ToStringBuilder.reflectionToString方法以CanalToStringStyle.DEFAULT_STYLE来转换

TimePosition

canal-1.1.4/protocol/src/main/java/com/alibaba/otter/canal/protocol/position/TimePosition.java

public class TimePosition extends Position {

    private static final long serialVersionUID = 6185261261064226380L;
    protected Long            timestamp;

    public TimePosition(Long timestamp){
        this.timestamp = timestamp;
    }

    public Long getTimestamp() {
        return timestamp;
    }

    public void setTimestamp(Long timestamp) {
        this.timestamp = timestamp;
    }

    //......
}

• TimePosition继承了Position，它定义了timestamp属性

EntryPosition

canal-1.1.4/protocol/src/main/java/com/alibaba/otter/canal/protocol/position/EntryPosition.java

public class EntryPosition extends TimePosition {

    private static final long serialVersionUID      = 81432665066427482L;
    public static final int   EVENTIDENTITY_SEGMENT = 3;
    public static final char  EVENTIDENTITY_SPLIT   = (char) 5;

    private boolean           included              = false;
    private String            journalName;
    private Long              position;
    // add by agapple at 2016-06-28
    private Long              serverId              = null;              // 记录一下位点对应的serverId
    private String            gtid                  = null;

    //......
}

• EntryPosition继承了TimePosition，它定义了included、journalName、position、serverId、gtid属性

SlaveEntryPosition

canal-1.1.4/parse/src/main/java/com/alibaba/otter/canal/parse/inbound/mysql/SlaveEntryPosition.java

public class SlaveEntryPosition extends EntryPosition {

    private static final long serialVersionUID = 5271424551446372093L;
    private final String      masterHost;
    private final String      masterPort;

    public SlaveEntryPosition(String fileName, long position, String masterHost, String masterPort){
        super(fileName, position);

        this.masterHost = masterHost;
        this.masterPort = masterPort;
    }

    public String getMasterHost() {
        return masterHost;
    }

    public String getMasterPort() {
        return masterPort;
    }
}

• SlaveEntryPosition继承了EntryPosition，它定义了masterHost、masterPort属性

LogPosition

canal-1.1.4/protocol/src/main/java/com/alibaba/otter/canal/protocol/position/LogPosition.java

public class LogPosition extends Position {

    private static final long serialVersionUID = 3875012010277005819L;
    private LogIdentity       identity;
    private EntryPosition     postion;

    public LogIdentity getIdentity() {
        return identity;
    }

    public void setIdentity(LogIdentity identity) {
        this.identity = identity;
    }

    public EntryPosition getPostion() {
        return postion;
    }

    public void setPostion(EntryPosition postion) {
        this.postion = postion;
    }

    //......
}

• LogPosition继承了Position，它定义了identity、postion两个属性

cursor

canal-1.1.4/meta/src/main/java/com/alibaba/otter/canal/meta/CanalMetaManager.java

public interface CanalMetaManager extends CanalLifeCycle {
    
    //......

    /**
     * 获取 cursor 游标
     */
    Position getCursor(ClientIdentity clientIdentity) throws CanalMetaManagerException;

    /**
     * 更新 cursor 游标
     */
    void updateCursor(ClientIdentity clientIdentity, Position position) throws CanalMetaManagerException;

    //......

}

• CanalMetaManager定义了getCursor、updateCursor方法；其中getCursor方法根据clientIdentity返回Position；updateCursor方法则更新指定clientIdentity的position

MemoryMetaManager

canal-1.1.4/meta/src/main/java/com/alibaba/otter/canal/meta/MemoryMetaManager.java

public class MemoryMetaManager extends AbstractCanalLifeCycle implements CanalMetaManager {

    protected Map>              destinations;
    protected Map batches;
    protected Map                  cursors;

    //......

    public Position getCursor(ClientIdentity clientIdentity) throws CanalMetaManagerException {
        return cursors.get(clientIdentity);
    }

    public void updateCursor(ClientIdentity clientIdentity, Position position) throws CanalMetaManagerException {
        cursors.put(clientIdentity, position);
    }

    //......
}

• MemoryMetaManager实现了CanalMetaManager接口，它定义了Map结构的cursors，key为ClientIdentity，value为Position；getCursor方法则根据clientIdentity从cursors获取Position；updateCursor方法则更新cursors中key为clientIdentity的value为position

小结

Position定义了toString方法，使用ToStringBuilder.reflectionToString方法以CanalToStringStyle.DEFAULT_STYLE来转换；它有两个直接子类，分别是TimePosition、LogPosition；而EntryPosition继承了TimePosition；SlaveEntryPosition继承了EntryPosition；LogPosition则组合了EntryPosition

doc

• Position