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Improved DB connection handling

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Support for aggressive connection timeouts, with exponential backoff
for multiple failures.
This commit is contained in:
Marco Cunha 2012-10-22 14:45:16 +02:00
parent e29484e14b
commit 34ae64706e
2 changed files with 118 additions and 60 deletions
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5
src/main/java/com/gmail/nossr50/runnables/SQLReconnect.java
View File

@ -15,9 +15,7 @@ public class SQLReconnect implements Runnable {
@Override
public void run() {
if (!Database.isConnected()) {
Database.connect();
if (Database.isConnected()) {
if (Database.checkConnection()) {
Users.saveAll(); //Save all profiles
Users.clearAll(); //Clear the profiles
@ -26,5 +24,4 @@ public class SQLReconnect implements Runnable {
}
}
}
}
}

157
src/main/java/com/gmail/nossr50/util/Database.java
View File

@ -22,24 +22,28 @@ public class Database {
private static String tablePrefix = configInstance.getMySQLTablePrefix();
private static Connection connection = null;
private static mcMMO plugin = null;
private static long reconnectTimestamp = 0;
// Scale waiting time by this much per failed attempt
private static final double SCALING_FACTOR = 5;
// Minimum wait in nanoseconds (default 500ms)
private static final long MIN_WAIT = 500*100000L;
// Maximum time to wait between reconnects (default 5 minutes)
private static final long MAX_WAIT = 5*60000000000L;
// How long to wait when checking if connection is valid (default 3 seconds)
private static final int VALID_TIMEOUT = 3;
// When next to try connecting to Database in nanoseconds
private static long nextReconnectTimestamp = 0L;
// How many connection attemtps have failed
private static int reconnectAttempt = 0;
public Database(mcMMO instance) {
plugin = instance;
connect(); //Connect to MySQL
// Load the driver instance
try {
Class.forName("com.mysql.jdbc.Driver");
DriverManager.getConnection(connectionString);
}
catch (ClassNotFoundException e) {
plugin.getLogger().warning(e.getLocalizedMessage());
}
catch (SQLException ex) {
plugin.getLogger().warning(ex.getLocalizedMessage());
printErrors(ex);
}
checkConnected(); //Connect to MySQL
}
/**
@ -49,6 +53,8 @@ public class Database {
try {
System.out.println("[mcMMO] Attempting connection to MySQL...");
// Force driver to load if not yet loaded
Class.forName("com.mysql.jdbc.Driver");
Properties connectionProperties = new Properties();
connectionProperties.put("autoReconnect", "false");
connectionProperties.put("maxReconnects", "0");
@ -57,9 +63,14 @@ public class Database {
System.out.println("[mcMMO] Connection to MySQL was a success!");
}
catch (SQLException ex) {
connection = null;
System.out.println("[mcMMO] Connection to MySQL failed!");
ex.printStackTrace();
printErrors(ex);
} catch (ClassNotFoundException ex) {
connection = null;
System.out.println("[mcMMO] MySQL database driver not found!");
ex.printStackTrace();
}
}
@ -185,7 +196,7 @@ public class Database {
* @return true if the query was successfully written, false otherwise.
*/
public boolean write(String sql) {
if (isConnected()) {
if (checkConnected()) {
try {
PreparedStatement statement = connection.prepareStatement(sql);
statement.executeUpdate();
@ -197,9 +208,6 @@ public class Database {
return false;
}
}
else {
attemptReconnect();
}
return false;
}
@ -214,7 +222,7 @@ public class Database {
ResultSet resultSet;
int result = 0;
if (isConnected()) {
if (checkConnected()) {
try {
PreparedStatement statement = connection.prepareStatement(sql);
resultSet = statement.executeQuery();
@ -232,45 +240,101 @@ public class Database {
printErrors(ex);
}
}
else {
attemptReconnect();
}
return result;
}
/**
* Get connection status
* Check connection status and re-establish if dead or stale.
*
* If the very first immediate attempt fails, further attempts
* will be made in progressively larger intervals up to MAX_WAIT
* intervals.
*
* This allows for MySQL to time out idle connections as needed by
* server operator, without affecting McMMO, while still providing
* protection against a database outage taking down Bukkit's tick
* processing loop due to attemping a database connection each
* time McMMO needs the database.
*
* @return the boolean value for whether or not we are connected
*/
public static boolean isConnected() {
if (connection == null) {
public static boolean checkConnected() {
boolean isClosed = true;
boolean isValid = false;
boolean exists = (connection != null);
// Initialized as needed later
long timestamp=0;
// If we're waiting for server to recover then leave early
if (nextReconnectTimestamp > 0 && nextReconnectTimestamp > System.nanoTime()) {
return false;
}
if (exists) {
try {
return connection.isValid(3);
isClosed = connection.isClosed();
} catch (SQLException e) {
isClosed = true;
e.printStackTrace();
printErrors(e);
}
catch (SQLException e) {
if (!isClosed) {
try {
isValid = connection.isValid(VALID_TIMEOUT);
} catch (SQLException e) {
// Don't print stack trace because it's valid to lose idle connections
// to the server and have to restart them.
isValid = false;
}
}
}
// Leave if all ok
if (exists && !isClosed && isValid) {
// Housekeeping
nextReconnectTimestamp = 0;
reconnectAttempt = 0;
return true;
}
// Cleanup after ourselves for GC and MySQL's sake
if (exists && !isClosed) {
try {
connection.close();
} catch (SQLException ex) {
// This is a housekeeping exercise, ignore errors
}
}
// Try to connect again
connect();
// Leave if connection is good
try {
if (connection != null && !connection.isClosed()) {
// Schedule a database save if we really had an outage
if (reconnectAttempt > 1) {
plugin.getServer().getScheduler().scheduleSyncDelayedTask(plugin, new SQLReconnect(plugin), 5);
}
nextReconnectTimestamp = 0;
reconnectAttempt = 0;
return true;
}
} catch (SQLException e) {
// Failed to check isClosed, so presume connection is bad and attempt later
e.printStackTrace();
printErrors(e);
}
reconnectAttempt++;
nextReconnectTimestamp = (long)(System.nanoTime() + Math.min(MAX_WAIT, (reconnectAttempt*SCALING_FACTOR*MIN_WAIT)));
return false;
}
}
/**
* Schedules a Sync Delayed Task with the Bukkit Scheduler to attempt reconnection after a minute has elapsed
* This will check for a connection being present or not to prevent unneeded reconnection attempts
*/
public static void attemptReconnect() {
final int RECONNECT_WAIT_TICKS = 60000;
final int RECONNECT_DELAY_TICKS = 1200;
if (reconnectTimestamp + RECONNECT_WAIT_TICKS < System.currentTimeMillis()) {
System.out.println("[mcMMO] Connection to MySQL was lost! Attempting to reconnect in 60 seconds..."); //Only reconnect if another attempt hasn't been made recently
reconnectTimestamp = System.currentTimeMillis();
plugin.getServer().getScheduler().scheduleSyncDelayedTask(plugin, new SQLReconnect(plugin), RECONNECT_DELAY_TICKS);
}
}
/**
* Read SQL query.
@ -282,7 +346,7 @@ public class Database {
ResultSet resultSet;
HashMap<Integer, ArrayList<String>> rows = new HashMap<Integer, ArrayList<String>>();
if (isConnected()) {
if (checkConnected()) {
try {
PreparedStatement statement = connection.prepareStatement(sql);
resultSet = statement.executeQuery();
@ -303,9 +367,6 @@ public class Database {
printErrors(ex);
}
}
else {
attemptReconnect();
}
return rows;
}