Reproduction of issue elastic/logstash#1675
vagrant up # apt-get logstash, create 5 log files with 1 message each
vagrant ssh
sleep 60 # wait for logstash to parse
sudo cat /var/log/upstart/logstash.log # logstash found all 5 messages
# 2014-08-29T21:39:50.637+0000 precise32 mymessage1
# 2014-08-29T21:39:50.642+0000 precise32 mymessage4
# 2014-08-29T21:39:50.648+0000 precise32 mymessage5
# 2014-08-29T21:39:50.651+0000 precise32 mymessage2
# 2014-08-29T21:39:50.664+0000 precise32 mymessage3
sudo service logstash restart
sleep 60 # wait for logstash to re-parse files
sudo cat /var/log/upstart/logstash.log # we see 9 events but only expected the original 5
# 2014-08-29T21:39:50.637+0000 precise32 mymessage1
# 2014-08-29T21:39:50.642+0000 precise32 mymessage4
# 2014-08-29T21:39:50.648+0000 precise32 mymessage5
# 2014-08-29T21:39:50.651+0000 precise32 mymessage2
# 2014-08-29T21:39:50.664+0000 precise32 mymessage3
# 2014-08-29T21:40:39.647+0000 precise32 mymessage4
# 2014-08-29T21:40:39.652+0000 precise32 mymessage5
# 2014-08-29T21:40:39.660+0000 precise32 mymessage2
# 2014-08-29T21:40:39.665+0000 precise32 mymessage3
cat /var/lib/logstash/.sincedb* # sincedb only records 1 out of 5 files
# 524303 0 64512 11