Most efficient way to update database

Question

I have a table that is auto-updating from time to time (say daily). All updated fields are of type TEXT, and might have lots of data. What I definitely know is that the data will not change a lot. Usually up to 30 characters added or deleted. So what would be more efficient? To merge somehow the changes or delete the old data and retrieve the new one? And, if the merge way is the way to do it, how should I do that? Is there any keyword or something in order to make this easier and more efficient?

P.S I am completely new to databases in general, it's the very first time I ever create and use a database, so sorry if it is a silly question

Answer 1

Due to the MVCC model, PostgreSQL always writes a new row for any set of changes applied in a single UPDATE. Doesn't matter, how much you change. There is no "merge way".

It's similar to (but not the same as) deleting the row and inserting a new one.

Since your columns are obviously big, they are going to be TOASTed, meaning they are compressed and stored out-of-line in a separate table. In an UPDATE, these columns can be preserved as-is if they remain unchanged, so it's considerably cheaper to UPDATE than to DELETE and INSERT. Quoting the manual here

During an UPDATE operation, values of unchanged fields are normally preserved as-is; so an UPDATE of a row with out-of-line values incurs no TOAST costs if none of the out-of-line values change.

If your rows have lots of columns and only some get updated a lot, it might pay to have two separate tables with a 1:1 relationship. But that's an extreme case.