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If you call $sth->fetchall_arrayref(undef,$max_rows) like you do, then your result will be an array of arrays, not an array of hashes, like you would like.

Moreover, your usage of $max_rows is not recommended. The docs state clearly that you should use a buffer to fetch records using that parameter.

# example from DBI docs my $max_rows=10_000; my $rows = []; # cache for batches of rows while( my $row = ( shift(@$rows) || shift(@{$rows=$sth->fetchall_arrayref({},$max_rows) || []}) ) ) { ... # do something with $row (not $rows, which is only the cache) }

Last, but not least, be aware that you are using the same statement handler for a outer and an inner loop. That is a mistake! The second "prepare" will reset $sth, and it will not continue fetching records. You must use two of them, one for fetching records, and one for updating.

Please see:

Update
Before trusting your code with 1 million records, try it with some smaller data set, to ensure that it's doing what you need.

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In reply to Re: DBI fetchall_arrayref using $max_size doesn't dereference normally. by gmax
in thread DBI fetchall_arrayref using $max_size doesn't dereference normally. by Tatnall

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