The problem can generally be written as "tuples seeing multiple
updates in the same transaction"?
I think that every time PostgreSQL is used with an ORM, there is
a certain amount of multiple updates taking place. I have actually
been reworking clientside to get around multiple updates, since they
popped up in one of my profiling runs. Allthough the time I optimized
away ended being both "roundtrip time" + "update time", but having
the database do half of it transparently, might have been sufficient
to get me to have had a bigger problem elsewhere..
To sum up. Yes I think indeed it is a real-world case.
Jesper
On the Python side, elixir and sqlalchemy have an excellent way of
handling this, basically when you start a transaction, all changes are
accumulated in a "session" object and only flushed to the database on
session commit (which is also generally the transaction commit). This has
multiple advantages, for instance it is able to issue multiple-line
statements, updates are only done once, you save a lot of roundtrips, etc.
Of course it is most of the time not compatible with database triggers, so
if there are triggers the ORM needs to be told about them.
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