Message aggregation

I configured syslog-ng to forward certain type of messages to a pipe. (say, ALERT). I wrote a program in perl to read from the pipe and print them out. The perl program first try to open the pipe and it'll block at the open function untill syslog-ng has some messages to write to the pipe. Then the perl program reads using IO::File can_read() function, with a 5 seconds timeout. So the function looks like this: $sel->can_read(5). Then I send 10 valid messages to syslog-ng from a remote machine by UDP. To my supprise, the perl program got only 2 of the 10! Then I send another 1 valid message to this syslog-ng after 5 minutes, and I got not only this message, but also the 8 I lost last time!

This happens only for the first 10 messages (which includes the opening of the pipe). Everything is fine after the first round. It looks like it's related to the pipe opening and messages get queued somewhere until later messages trigger the queue to flush.