Allow to include the current version in history table

[mcesar]

No description provided.

[dekiesel]

I'd be pretty interested in this too since this makes it much easier to see current and historic data at a glance.

[simoneb]

@mcesar can you please explain what this PR does and the motivation why you would need this?

[mcesar]

@simoneb this PR gives the option to store the current version in history table together with the old versions. When applied, it will provide a easier way to query data given a timestamp. For example, given a table t(id integer, name text, sys_period tstzrange), we want to query the version at a timestamp x:

a. current behavior:

SELECT * FROM t WHERE x <@ sys_period
UNION
SELECT * FROM t_history WHERE x <@ sys_period;

b. with include_current_version_in_history=true:

SELECT * FROM t_history WHERE x <@ sys_period;

[simoneb]

Considering that this has a simple solution in user space and that it would deviate from the original implementation that we're trying to adhere to, I don't see a compelling reason to include this feature, but happy to be convinced otherwise

[mcesar]

I see, I assumed that deviation from original implementation was not an issue because of this part of the readme:

Over time, new features have been introduced while maintaining backward compatibility: (...)

[simoneb]

It's not an issue per-se, but this has a very simple solution in user space

[dekiesel]

As the number of tables grows so does the number of workarounds.

I am versioning 21 tables and I have to create 21 views when stepping through historic data. This PR would simplify my life by a lot.

[simoneb]

If there is demand for this feature, I'm not strongly against including it. We just need to make sure that, if possible, this doesn't result in a breaking change for existing users, and that the default will remain that of not including the current version in the history table.

[rohaldb]

This I would find this extremely useful. Running the union for me is prohibitively expensive at inference time, meaning I then have to introduce a delay to do it periodically using cron.

[leventea1]

@mcesar can you update versioning_function_nochecks.sql and document it in Readme as well.
You might also want to consider mcesar#2
FYI @simoneb

[leventea1]

lgtm

[kieranswhite]

@mcesar @dekiesel @rohaldb I am going to close this PR as we have taken changes proposed by @mcesar and merged them in to the extension along with a few small additions. It's been released under version v0.6.0. Thanks all!