Can anyone explain to me what this mean in online.log?

02:31:14 Process exited with return code 139: /bin/sh /bin/sh -c /usr/informix/etc/log_full.sh 2 23 "Logical Log 2333 Complete." "Logical Log 2333 Complete."


And also will the fiel size of online.log affect performance?

This indicates that the ALARMPROGRAM failed or more
specifically did not return with exit code 0.
Your log backup did not finish successfully.

If you are using 'onbar', take a look at the onbar activity
log (BAR_ACT_LOG parameter in $ONCONFIG) to get
more information.
You might also trying to backup your logs manually
with (onbar -b -l) and see what is happening.
139 seems to be the returncode from the 'onbar' process
and means BAD_VERSION. So I guess that the entries in sysutils:bar_version (or $INFORMIXDIR/etc/sm_versions for newer releases of the Informix databaseserver) ) are not correctly.
.

I'm actually using ontape to do daily backup (ontape -s -L 0) and also logical log backup (ontape -c). How to I configure ? Is it onbar better than ontape?

If you use the continuous backup mechanism of
ontape, then you should set your ALARMPROGRAM
to:

$INFORMIXDIR/etc/no_log.sh

This will prevent the errors reported in the 'online.log'.

onbar is more complicated than ontape. It has advanced
features such as parallel backup to more than one
device, point-in-time restore, backup-history-database
etc.

However if you don't have a database of several
hundred gigabytes, I would recommend that you
stay with ontape. This solution is simple and easy
to use.

You will find more information in the 'Backup & Restore Guide'.

Is this mean that the logical log will be automatically backup when it's full? And is it mean that if I want to test Data Replication, I have to use onbar concept?

When you start 'ontape -c' the logical log will be
automatically backed up as soon as it is full.

You can setup HDR with onbar and ontape.