while (<DATA>)
{
	chomp;
	my @a=split/\s+/;
	push @{$h{$a[0]}},$a[1];
}
$"="\t";
print "$_\n@{$h{$_}}\n\n" for sort keys  %h;

__DATA__
log1    123
log1    233
log1    223
log2    465
log2    231
log2    456