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本文主要研究一下hikari连接池的maxLifetime属性及evict操作
maxLifetime属性及evict操作
maxLifetime
用来设置一个connection在连接池中的存活时间，默认是1800000，即30分钟。如果设置为0，表示存活时间无限大。如果不等于0且小于30秒则会被重置回30分钟。
evict
用来标记连接池中的连接不可用，这样在borrow连接的时候，如果是标记evict的，则会继续获取连接
/**
* Get a connection from the pool, or timeout after the specified number of milliseconds.
*
* @param hardTimeout the maximum time to wait for a connection from the pool
* @return a java.sql.Connection instance
* @throws SQLException thrown if a timeout occurs trying to obtain a connection
*/
public Connection getConnection(final long hardTimeout) throws SQLException
{
suspendResumeLock.acquire();
final long startTime = currentTime();
try {
long timeout = hardTimeout;
do {
PoolEntry poolEntry = connectionBag.borrow(timeout, MILLISECONDS);
if (poolEntry == null) {
break; // We timed out... break and throw exception
}
final long now = currentTime();
if (poolEntry.isMarkedEvicted() || (elapsedMillis(poolEntry.lastAccessed, now) > ALIVE_BYPASS_WINDOW_MS && !isConnectionAlive(poolEntry.connection))) {
closeConnection(poolEntry, poolEntry.isMarkedEvicted() ? EVICTED_CONNECTION_MESSAGE : DEAD_CONNECTION_MESSAGE);
timeout = hardTimeout - elapsedMillis(startTime);
}
else {
metricsTracker.recordBorrowStats(poolEntry, startTime);
return poolEntry.createProxyConnection(leakTaskFactory.schedule(poolEntry), now);
}
} while (timeout > 0L);
metricsTracker.recordBorrowTimeoutStats(startTime);
throw createTimeoutException(startTime);
}
catch (InterruptedException e) {
Thread.currentThread().interrupt();
throw new SQLException(poolName + " - Interrupted during connection acquisition", e);
}
finally {
suspendResumeLock.release();
}
}
注意，这里如果取到的连接是poolEntry.isMarkedEvicted()，则会close掉，同时更新timeout值，然后继续循环borrow连接
HikariPool.evictConnection
HikariCP-2.7.6-sources.jar!/com/zaxxer/hikari/pool/HikariPool.java
/**
* Evict a Connection from the pool.
*
* @param connection the Connection to evict (actually a {@link ProxyConnection})
*/
public void evictConnection(Connection connection)
{
ProxyConnection proxyConnection = (ProxyConnection) connection;
proxyConnection.cancelLeakTask();
try {
softEvictConnection(proxyConnection.getPoolEntry(), "(connection evicted by user)", !connection.isClosed() /* owner */);
}
catch (SQLException e) {
// unreachable in HikariCP, but we're still forced to catch it
}
}
这种是主动调用evictConnection的场景
HikariPool.createPoolEntry
HikariCP-2.7.6-sources.jar!/com/zaxxer/hikari/pool/HikariPool.java
/**
* Creating new poolEntry. If maxLifetime is configured, create a future End-of-life task with 2.5% variance from
* the maxLifetime time to ensure there is no massive die-off of Connections in the pool.
*/
private PoolEntry createPoolEntry()
{
try {
final PoolEntry poolEntry = newPoolEntry();
final long maxLifetime = config.getMaxLifetime();
if (maxLifetime > 0) {
// variance up to 2.5% of the maxlifetime
final long variance = maxLifetime > 10_000 ? ThreadLocalRandom.current().nextLong( maxLifetime / 40 ) : 0;
final long lifetime = maxLifetime - variance;
poolEntry.setFutureEol(houseKeepingExecutorService.schedule(
() -> {
if (softEvictConnection(poolEntry, "(connection has passed maxLifetime)", false /* not owner */)) {
addBagItem(connectionBag.getWaitingThreadCount());
}
},
lifetime, MILLISECONDS));
}
return poolEntry;
}
catch (Exception e) {
if (poolState == POOL_NORMAL) { // we check POOL_NORMAL to avoid a flood of messages if shutdown() is running concurrently
LOGGER.debug("{} - Cannot acquire connection from data source", poolName, (e instanceof ConnectionSetupException ? e.getCause() : e));
}
return null;
}
}
/**
* "Soft" evict a Connection (/PoolEntry) from the pool. If this method is being called by the user directly
* through {@link com.zaxxer.hikari.HikariDataSource#evictConnection(Connection)} then {@code owner} is {@code true}.
*
* If the caller is the owner, or if the Connection is idle (i.e. can be "reserved" in the {@link ConcurrentBag}),
* then we can close the connection immediately. Otherwise, we leave it "marked" for eviction so that it is evicted
* the next time someone tries to acquire it from the pool.
*
* @param poolEntry the PoolEntry (/Connection) to "soft" evict from the pool
* @param reason the reason that the connection is being evicted
* @param owner true if the caller is the owner of the connection, false otherwise
* @return true if the connection was evicted (closed), false if it was merely marked for eviction
*/
private boolean softEvictConnection(final PoolEntry poolEntry, final String reason, final boolean owner)
{
poolEntry.markEvicted();
if (owner || connectionBag.reserve(poolEntry)) {
closeConnection(poolEntry, reason);
return true;
}
return false;
}
注意在createPoolEntry的时候注册了一个延时任务，并通过poolEntry.setFutureEol设置到poolEntry中
softEvictConnection，首先标记markEvicted。然后如果是用户自己调用的，则直接关闭连接；如果从connectionBag中标记不可borrow成功，则关闭连接
这个定时任务是在每次createPoolEntry的时候，根据maxLifetime随机设定一个variance，在maxLifetime - variance之后触发evict
小结
hikari连接池的maxLifetime用来标记connection在连接池中的存活时间，为0表示无限期。其到期的操作，主要是依靠在创建poolEntry的时候，注册一个延时任务，在连接存活将要到达maxLifetime之前触发evit，用来防止出现大面积的connection因maxLifetime同一时刻失效。除了这个延时任务，用户也可以主动去调用evict标记连接为evict。
触发时间距离maxlifetime的差值是根据 maxLifetime > 10_000 ? ThreadLocalRandom.current().nextLong( maxLifetime / 40 ) : 0;
来计算(up to 2.5% of the maxlifetime)。
标记为evict只是表示连接池中的该连接不可用，但还在连接池当中，还会被borrow出来，只是getConnection的时候判断了，如果是isMarkedEvicted，则会从连接池中移除该连接，然后close掉。
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