I am working on postgres replication stream API. While working on it came across unusual behavior.
When I use replication slot writing whole code inside main block, everything works fine.
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();
}
}
}
But when I try to separate stream logic using separate method like this
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, offset, 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, 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;
try {
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();
} catch (SQLException e) {
e.printStackTrace();
}
return stream;
}
}
After reading some data, program is giving error
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
I don't see any difference between both approach. But the program is behaving differently. Can someone explain, what is wrong with second approach.
