If I understand ikegami correctly, you can only use a DB handle in the thread that created it. Regardless of any concurrent operations.

I didn't say that. It might be true, but it's not what I said.

I said you couldn't share one.

So how could multiple threads have a copy of the handle if it can't be shared? Through the cloning process that happens a new thread is created.

my $x = 123;

( async {
   $x = 456;
   say $x;  # 456
} )->join();

say $x;  # 123
[download]

There are two $x since the entire interpreter is cloned when it creates a thread.

There's even a callback that allows libraries with external resources to clone themselves. Whether DBI and DBD::SQLite takes advantage of that or not is unknown to me. But I find it unlikely. How do you clone a database connection? So it's probably true that one can only use DB handle in the thread that created it.