Free large cached payloads. Fixes #1587

If the ServerSession's payload cache has grown larger than the maximum size of a single packet, free it when the session is returned to the pool so that the memory can be reclaimed.

Author: bgrainger

src/MySqlConnector/Core/ServerSession.cs

@@ -74,6 +74,11 @@ public ValueTask ReturnToPoolAsync(IOBehavior ioBehavior, MySqlConnection? ownin
 		LastReturnedTimestamp = Stopwatch.GetTimestamp();
 		if (Pool is null)
 			return default;
+
+		// if the payload cache is too large, discard it rather than keeping it alive in the pool; see https://github.com/mysql-net/MySqlConnector/issues/1587
+		if (m_payloadCache.Array?.Length > ProtocolUtility.MaxPacketSize + 1)
+			m_payloadCache.ArraySegment = default;
+
 		MetricsReporter.RecordUseTime(Pool, Utility.GetElapsedSeconds(LastLeasedTimestamp, LastReturnedTimestamp));
 		LastLeasedTimestamp = 0;
 		return Pool.ReturnAsync(ioBehavior, this);