Add elapsed time in update index command

[pauloxnet]

I moved the transaction.atomic from decorator to context manager and added the elapsed time information in the command output.

I used this code to perform this check on the documentation update in the issue #1693

See #1693 (comment)

[bmispelon]

I'm a bit late to the party here (didn't have time to review this last night).

I don't really understand the reasoning behind moving the code from a decorator to a context manager, could you expand on that?

Since the PR had no tests (which I understand might be a little tricky to write), there's not really anything preventing someone from reverting to a decorator in the future. If this is about performance, a comment indicating that would be helpful.

[pauloxnet]

I don't really understand the reasoning behind moving the code from a decorator to a context manager, could you expand on that?

Following the Django documentation about "Database transactions":

"Open transactions have a performance cost for your database server. To minimize this overhead, keep your transactions as short as possible."

I wanted to leave in the transaction only the two lines of code for which it made sense to have it, leaving out the calculation of the elapsed time or the writing to the terminal.

Since the PR had no tests (which I understand might be a little tricky to write), there's not really anything preventing someone from reverting to a decorator in the future. If this is about performance, a comment indicating that would be helpful.

I agree that a comment would be nice, and if you want I can add it, but the short-term goal is to convert the vector search field to a generated field (see #1650), which will allow us to completely remove the need to perform this update.