java – 为什么Postgres Replication Stream在单独的函数中使用时不起作用？

我正在研究postgres复制流API.在努力工作时遇到了不寻常的行为.

当我使用复制槽在主块内写入整个代码时,一切正常.

public class Server implements Config {

public static void main(String[] args) {
    Properties prop = new Properties();
    prop.load(new FileInputStream(System.getProperty("prop")));

    String user = prop.getProperty("user");
    String password = prop.getProperty("password");
    String url = prop.getProperty("url");

    Properties props = new Properties();
    PGProperty.USER.set(props,user);
    PGProperty.PASSWORD.set(props,password);
    PGProperty.ASSUME_MIN_SERVER_VERSION.set(props,"9.4");
    PGProperty.REPLICATION.set(props,"database");
    PGProperty.PREFER_QUERY_MODE.set(props,"simple");

    Connection conn= null;
    PGConnection replicationConnection= null;
    PGReplicationStream stream = null;

        conn = DriverManager.getConnection(url,props);
        replicationConnection = conn.unwrap(PGConnection.class);
        stream = replicationConnection.getReplicationAPI().replicationStream().logical()
                .withSlotName("replication_slot")
                .withSlotOption("include-xids",true)
                .withSlotOption("include-timestamp","on")
                .withSlotOption("skip-empty-xacts",true)
                .withStatusInterval(20,TimeUnit.SECONDS).start();

    while (true) {
            ByteBuffer msg;
            try {
                msg = stream.readPending();         

            if (msg == null) {
                TimeUnit.MILLISECONDS.sleep(10L);
                continue;
            }

            int offset = msg.arrayOffset();
            byte[] source = msg.array();
            int length = source.length - offset;
            // convert byte buffer into string
            String data = new String(source,offset,length);

            // then convert it into bufferedreader
            BufferedReader reader = new BufferedReader(new StringReader(data));
            String line = reader.readLine();

            while (line != null) {
                System.out.println(line);
                line = reader.readLine();
            }
            stream.setAppliedLSN(stream.getLastReceiveLSN());
            stream.setFlushedLSN(stream.getLastReceiveLSN());
        } catch (sqlException | IOException | InterruptedException e) {
            // Todo Auto-generated catch block
            e.printstacktrace();
        }
        }
}

但是当我尝试使用这样的单独方法分离流逻辑时

public class Server implements Config {

public static void main(String[] args) {
    PGReplicationStream stream = getReplicationStream();
        while (true) {
            ByteBuffer msg;
            try {
                msg = stream.readPending();
    if (msg == null) {
                TimeUnit.MILLISECONDS.sleep(10L);
                continue;
            }

            int offset = msg.arrayOffset();
            byte[] source = msg.array();
            int length = source.length - offset;
            String data = new String(source,length);

            BufferedReader reader = new BufferedReader(new StringReader(data));
            String line = reader.readLine();

            while (line != null) {
                System.out.println(line);
                line = reader.readLine();
            }
            stream.setAppliedLSN(stream.getLastReceiveLSN());
            stream.setFlushedLSN(stream.getLastReceiveLSN());
        } catch (sqlException | IOException | InterruptedException e) {
            e.printstacktrace();
        }
        }

}
public static PGReplicationStream getReplicationStream() {
    Properties prop = new Properties();
    try {
        prop.load(new FileInputStream(System.getProperty("prop")));
    } catch (IOException e1) {
        // Todo Auto-generated catch block
        e1.printstacktrace();
    }

    String user = prop.getProperty("user");
    String password = prop.getProperty("password");
    String url = prop.getProperty("url");

    Properties props = new Properties();
    PGProperty.USER.set(props,"simple");

    Connection conn= null;
    PGConnection replicationConnection= null;
    PGReplicationStream stream = null;
    try {
        conn = DriverManager.getConnection(url,TimeUnit.SECONDS).start();
    } catch (sqlException e) {
        e.printstacktrace();
    }
    return stream;
}

}

读完一些数据后,程序出错了

org.postgresql.util.PsqlException: Database connection Failed when reading from copy
at org.postgresql.core.v3.QueryExecutorImpl.readFromcopy(QueryExecutorImpl.java:1028)
at org.postgresql.core.v3.copyDualImpl.readFromcopy(copyDualImpl.java:41)
at org.postgresql.core.v3.replication.V3PGReplicationStream.receiveNextData(V3PGReplicationStream.java:155)
at org.postgresql.core.v3.replication.V3PGReplicationStream.readInternal(V3PGReplicationStream.java:124)
at org.postgresql.core.v3.replication.V3PGReplicationStream.readPending(V3PGReplicationStream.java:78)
at Server.main(Server.java:47)
Caused by: java.net.socketException: Socket closed
at java.net.socketInputStream.socketRead0(Native Method)
at java.net.socketInputStream.socketRead(SocketInputStream.java:116)
at java.net.socketInputStream.read(SocketInputStream.java:171)
at java.net.socketInputStream.read(SocketInputStream.java:141)
at org.postgresql.core.VisibleBufferedInputStream.readMore(VisibleBufferedInputStream.java:140)
at org.postgresql.core.VisibleBufferedInputStream.ensureBytes(VisibleBufferedInputStream.java:109)
at org.postgresql.core.VisibleBufferedInputStream.read(VisibleBufferedInputStream.java:191)
at org.postgresql.core.PGStream.receive(PGStream.java:495)
at org.postgresql.core.PGStream.receive(PGStream.java:479)
at org.postgresql.core.v3.QueryExecutorImpl.processcopyResults(QueryExecutorImpl.java:1161)
at org.postgresql.core.v3.QueryExecutorImpl.readFromcopy(QueryExecutorImpl.java:1026)
... 5 more

我认为两种方法之间没有任何区别.但该计划表现不同.有人可以解释,第二种方法有什么问题.

解决方法

我相信你的问题与连接.一旦你的函数返回它就会超出范围,并且垃圾收集器会收集并最终确定它.在最终确定中,连接已关闭,然后您的程序可能会失败.尝试在main方法中可用的范围内移动连接和其他所需的中间变量,然后重试.

原文地址：https://www.jb51.cc/java/129840.html