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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，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(); } } 复制代码

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

讯享网 / * 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 } } 复制代码

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

讯享网

 / * 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; } 复制代码

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。

doc

• configuration-knobs-baby