This is a bit technical and arcane, but I want to mention it because I’ve seen a lot of recent patches still using the old style of code calling $sth->finish() explicitly. I know a lot of the codebase still does this internally, but for Koha such usage is almost always wrong.
If this were just my personal contention, I would couch this in terms of an RFC to deprecate the usage. But we don’t get a choice here: DBI is telling us “don’t do it”.
Please refer to the DBI perldoc:
The finish method is rarely needed, and frequently overused, but can sometimes be helpful in a few very specific situations to allow the server to free up resources (such as sort buffers).
When all the data has been fetched from a SELECT statement, the driver should automatically call finish for you. So you should not normally need to call it explicitly except when you know that you’ve not fetched all the data from a statement handle. The most common example is when you only want to fetch one row, but in that case the selectrow_* methods are usually better anyway. Adding calls to finish after each fetch loop is a common mistake, don’t do it, it can mask genuine problems like uncaught fetch errors.
That last sentence is the most concrete and important (hence my bolding). Moral of the story: don’t do it. Or if you think you have to, at least comment why, like:
$sth->finish(); # FIXME: leaving data unfetched, should rework query
