change default maxLifetime variance from 2.5% to 25% to further avoid mass connection die-off dips

CHANGES

@@ -1,8 +1,12 @@
 HikariCP Changes
 
+Changes in 6.0.1
+
+ * change default maxLifetime variance from 2.5% to 25% to further avoid mass connection die-off dips
+
 Changes in 6.0.0
 
- * fixed #2152 duplicate connection in try with resources clause caused close() being called twice on each connection.
+ * fixed #2152 duplicate connection in try with resources clause caused close() being called twice on each connection
 
  * merged #2226 consistent handling of errorCode and sqlState in timeout exception
 

src/main/java/com/zaxxer/hikari/pool/HikariPool.java

@@ -64,6 +64,7 @@ public final class HikariPool extends PoolBase implements HikariPoolMXBean, IBag
 
    private final long aliveBypassWindowMs = Long.getLong("com.zaxxer.hikari.aliveBypassWindowMs", MILLISECONDS.toMillis(500));
    private final long housekeepingPeriodMs = Long.getLong("com.zaxxer.hikari.housekeeping.periodMs", SECONDS.toMillis(30));
+   private final long lifeTimeVarianceFactor = Math.min(40, Math.max(2, Long.getLong("com.zaxxer.hikari.lifeTimeVarianceFactor", 4))); // variance% = 100 / factor
    private final boolean isRequestBoundariesEnabled = Boolean.getBoolean("com.zaxxer.hikari.enableRequestBoundaries");
 
    private static final String EVICTED_CONNECTION_MESSAGE = "(connection was evicted)";
@@ -470,7 +471,7 @@ public final class HikariPool extends PoolBase implements HikariPoolMXBean, IBag
    // ***********************************************************************
 
    /**
-    * Creating new poolEntry.  If maxLifetime is configured, create a future End-of-life task with 2.5% variance from
+    * Creating new poolEntry. If maxLifetime is configured, create a future End-of-life task with variance from
     * the maxLifetime time to ensure there is no massive die-off of Connections in the pool.
     */
    private PoolEntry createPoolEntry()
@@ -480,8 +481,8 @@ public final class HikariPool extends PoolBase implements HikariPoolMXBean, IBag
 
          final var maxLifetime = config.getMaxLifetime();
          if (maxLifetime > 0) {
-            // variance up to 2.5% of the maxlifetime
-            final var variance = maxLifetime > 10_000 ? ThreadLocalRandom.current().nextLong( maxLifetime / 40 ) : 0;
+            // default variance upto 25% of the maxLifetime (random)
+            final var variance = maxLifetime > 10_000L ? ThreadLocalRandom.current().nextLong( maxLifetime / lifeTimeVarianceFactor ) : 0L;
             final var lifetime = maxLifetime - variance;
             poolEntry.setFutureEol(houseKeepingExecutorService.schedule(new MaxLifetimeTask(poolEntry), lifetime, MILLISECONDS));
          }
@@ -605,11 +606,11 @@ public final class HikariPool extends PoolBase implements HikariPoolMXBean, IBag
    /**
     * "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}.
-    *
+    * <p>
     * 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.
-    *
+    * <p>
     * @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
@@ -683,7 +684,7 @@ public final class HikariPool extends PoolBase implements HikariPoolMXBean, IBag
     * timeout, e.g. a SQLException thrown by the driver while trying to create a new Connection, then use the
     * SQL State from that exception as our own and additionally set that exception as the "next" SQLException inside
     * our exception.
-    *
+    * <p>
     * As a side effect, log the timeout failure at DEBUG, and record the timeout failure in the metrics tracker.
     *
     * @param startTime the start time (timestamp) of the acquisition attempt