聊聊hikari连接池的idleTimeout及minimumIdle属性

2023-11-11 00:47| 来源: 网络整理| 查看: 265

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本文主要研究一个hikari连接池的idleTimeout及minimumIdle属性

idleTimeout

默认是600000毫秒，即10分钟。如果idleTimeout+1秒>maxLifetime 且 maxLifetime>0，则会被重置为0；如果idleTimeout!=0且小于10秒，则会被重置为10秒。如果idleTimeout=0则表示空闲的连接在连接池中永远不被移除。

只有当minimumIdle小于maximumPoolSize时，这个参数才生效，当空闲连接数超过minimumIdle，而且空闲时间超过idleTimeout，则会被移除。

minimumIdle

控制连接池空闲连接的最小数量，当连接池空闲连接少于minimumIdle，而且总共连接数不大于maximumPoolSize时，HikariCP会尽力补充新的连接。为了性能考虑，不建议设置此值，而是让HikariCP把连接池当做固定大小的处理，默认minimumIdle与maximumPoolSize一样。

当minIdlemaxPoolSize,则被重置为maxPoolSize，该值默认为10。

HikariPool.HouseKeeper

HikariCP-2.7.6-sources.jar!/com/zaxxer/hikari/pool/HikariPool.java

private final long HOUSEKEEPING_PERIOD_MS = Long.getLong("com.zaxxer.hikari.housekeeping.periodMs", SECONDS.toMillis(30)); this.houseKeeperTask = houseKeepingExecutorService.scheduleWithFixedDelay(new HouseKeeper(), 100L, HOUSEKEEPING_PERIOD_MS, MILLISECONDS); /** * The house keeping task to retire and maintain minimum idle connections. */ private final class HouseKeeper implements Runnable { private volatile long previous = plusMillis(currentTime(), -HOUSEKEEPING_PERIOD_MS); @Override public void run() { try { // refresh timeouts in case they changed via MBean connectionTimeout = config.getConnectionTimeout(); validationTimeout = config.getValidationTimeout(); leakTaskFactory.updateLeakDetectionThreshold(config.getLeakDetectionThreshold()); final long idleTimeout = config.getIdleTimeout(); final long now = currentTime(); // Detect retrograde time, allowing +128ms as per NTP spec. if (plusMillis(now, 128) < plusMillis(previous, HOUSEKEEPING_PERIOD_MS)) { LOGGER.warn("{} - Retrograde clock change detected (housekeeper delta={}), soft-evicting connections from pool.", poolName, elapsedDisplayString(previous, now)); previous = now; softEvictConnections(); return; } else if (now > plusMillis(previous, (3 * HOUSEKEEPING_PERIOD_MS) / 2)) { // No point evicting for forward clock motion, this merely accelerates connection retirement anyway LOGGER.warn("{} - Thread starvation or clock leap detected (housekeeper delta={}).", poolName, elapsedDisplayString(previous, now)); } previous = now; String afterPrefix = "Pool "; if (idleTimeout > 0L && config.getMinimumIdle() < config.getMaximumPoolSize()) { logPoolState("Before cleanup "); afterPrefix = "After cleanup "; final List notInUse = connectionBag.values(STATE_NOT_IN_USE); int toRemove = notInUse.size() - config.getMinimumIdle(); for (PoolEntry entry : notInUse) { if (toRemove > 0 && elapsedMillis(entry.lastAccessed, now) > idleTimeout && connectionBag.reserve(entry)) { closeConnection(entry, "(connection has passed idleTimeout)"); toRemove--; } } } logPoolState(afterPrefix); fillPool(); // Try to maintain minimum connections } catch (Exception e) { LOGGER.error("Unexpected exception in housekeeping task", e); } } }

这个HouseKeeper是一个定时任务，在HikariPool构造器里头初始化，默认的是初始化后100毫秒执行，之后每执行完一次之后隔HOUSEKEEPING_PERIOD_MS(30秒)时间执行。这个定时任务的作用就是根据idleTimeout的值，移除掉空闲超时的连接。首先检测时钟是否倒退，如果倒退了则立即对过期的连接进行标记evict；之后当idleTimeout>0且配置的minimumIdle 0 || getIdleConnections() < config.getMinimumIdle()); } }

shouldCreateAnotherConnection方法决定了是否需要添加新的连接

createPoolEntry /** * 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; } }

createPoolEntry方法创建一个poolEntry，同时给它的lifetime过期设定了一个延时任务。

小结 HouseKeeper是一个定时任务，在HikariPool构造器里头初始化，默认的是初始化后100毫秒执行，之后每执行完一次之后隔HOUSEKEEPING_PERIOD_MS(30秒)时间执行。如果发现时钟倒退，则立即标记evict连接，然后退出；否则都会执行fillPool，来试图维持空闲连接到minimumIdle的数值当idleTimeout>0且配置的minimumIdle

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