Hello Wise Ones-

I'm in the process of refactoring my code, and I have found a number of mistakes that we had previously made using DBI. While we are now properly using prepared statements with placeholders, in referencing the following (old) post: Tricks with DBI, I found myself getting confused on a couple of areas... Here's the general logic of what I have:

# connect parent
$dbh->connect(...);

#statement 1
$sth=$dbh->prepare($sql);
$sth->execute;
while(($var)=$sth->fetchrow_array) {

    # fork
    $pm->start and next;

    # connect child
    $dbh2->connect(...);

    #statement 2
    $sth2->prepare($sql2);
    $sth2->execute;
    while(($var2)=$sth2->fetchrow_array) {

        # condition
        if($var) {
            # statement 3 that might not be called
            $sth3->prepare($sql3);
            $sth3->execute;
            while(($var3)=$sth3->fetchrow_array) { ... }
            $sth3->finish;
        } else {
            # statement 4 that might not be called
            $sth4->prepare($sql4);
            $sth4->execute;
            while(($var4)=$sth4->fetchrow_array) { ... }
            $sth4->finish;
        }

    }
    # finish statement 2
    $sth2->finish;

    # disconnect child
    $dbh2->disconnect;

    # end fork
    $pm->finish;
    
}
# finish statement 1
$sth->finish;

# disconnect parent
$dbh->disconnect;
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With that, I have a handful of questions:

1. I read that I need to start a new $dbh within each child (which I have done above). Is that correct?
2. $sth and $sth2 don't seem that they need to be in a prepare_cached(), however $sth3 and $sth4 need to be handled better since they are in a while() loop and may get called multiple times. If I use prepare_cached() here, were would I call the finish()? Or should I just use prepare() and move the prepare()/finish() statements outside of the while loop (then I'm preparing the statement even if it never gets used)?
3. Is using $sth->bind_columns and $sth->fetch faster/more efficient/preferred to using $sth->fetchrow_array?
4. Is there anything else that I am doing wrong or can do better with my logic above?

Thank you in advance!