====== SIGUSR1 received.  Doing graceful restart ======

<file>
[Mon Sep 21 23:44:09.650215 2015] [mpm_event:notice]
[pid 188:tid 2945215190848] AH00493: SIGUSR1 received.  Doing graceful restart
</file>

The warnings messages "SIGUSR1 received. Doing graceful restart "are normals and are related to the log rotation. They has no impact on site performance.