Rather than iterating through an array to find a match like this

foreach $line (<LOGFILE1>) {
  chomp($line); 
  foreach $childid (@Task_id) {
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build a hash and use the keys to match

#!/usr/bin/perl
use strict;

my %data = ();
my @id   = ();
my $reqid = '8274';

my $infile  = 'worker.log';
my $outfile = 'data.CSV';
open IN,'<',$infile or die "$!";

# input
while (<IN>) {
  chomp;
  next unless /Task:id=(\d+)/;

  my $taskid = $1;
  my (undef,$timestamp,undef)  = split /\s+/,$_,3;
  
  if (/(Started|Done).+topic (\d+_(\d+)_.+)/){
    $data{$3}{$1}      = $timestamp;
    $data{$3}{'Topic'} = $2;
  }

  while ( /\{(\d+)-SUCCESSFUL\}/g ){
    push @id,$1 if ($taskid eq $reqid);
  }
}
close IN;

# output
open OUT,'>',$outfile or die "$!";
my @cols = qw(Topic Started Done);
printf OUT "%s,%s,%s\n",@cols;
for my $id (sort @id){
  if (exists $data{$id}){
    printf OUT "%s,%s,%s\n", map { $data{$id}{$_} } @cols;
  } else {
    print OUT "$id - no data\n";
  }
}
close OUT;
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