why lighttpd complain "sendfile: Broken pipe 32 "

[Ken Chen]

What causes this happen?

2007-12-12 21:17:47: (network_freebsd_sendfile.c.173) sendfile:  Broken pipe
32
2007-12-12 21:17:47: (connections.c.603) connection closed: write failed on
fd 149
2007-12-12 21:19:19: (network_freebsd_sendfile.c.173) sendfile:  Broken pipe
32
2007-12-12 21:19:19: (connections.c.603) connection closed: write failed on
fd 476
2007-12-12 21:19:19: (network_freebsd_sendfile.c.173) sendfile:  Broken pipe
32
2007-12-12 21:19:19: (connections.c.603) connection closed: write failed on
fd 476
2007-12-12 21:20:30: (network_freebsd_sendfile.c.173) sendfile:  Broken pipe
32
2007-12-12 21:20:30: (connections.c.603) connection closed: write failed on
fd 158
2007-12-12 21:20:30: (network_freebsd_sendfile.c.173) sendfile:  Broken pipe
32
2007-12-12 21:20:30: (connections.c.603) connection closed: write failed on
fd 158

web# sysctl -a | grep maxfiles
kern.maxfiles: 32768
kern.maxfilesperproc: 32768
web# netstat -m
2126/1654/3780 mbufs in use (current/cache/total)
793/495/1288/25600 mbuf clusters in use (current/cache/total/max)
855/2538/6656 sfbufs in use (current/peak/max)
2117K/1403K/3521K bytes allocated to network (current/cache/total)
0 requests for sfbufs denied
0 requests for sfbufs delayed
273045 requests for I/O initiated by sendfile
325 calls to protocol drain routines

web# uname -a
FreeBSD web 6.0-RELEASE FreeBSD 6.0-RELEASE #4: Tue Dec 11 18:30:27 CST
2007     root at web:/usr/src/sys/i386/compile/WEB  i386