[Mobilitydb-dev] Initial MEOS implementation

[Krishna Chaitanya]

Dear Professor,

This is really great progress, thanks for the update. As such, everything
looks good to me. Once timezone management and documentation is also in
place, I think MEOS should be in a really good position, unlocking a lot of
possibilities of extension on top of it. Even from a technical architecture
perspective as well the build process and everything else seems perfect.

The only minor question which I had, although I did not dive into it in too
much detail myself, is whether the borrowing of code from postgres to meos
could at any time backfire. I understand this is necessary to make things
easier to allow reusability of common definitions of for example
timestamp/timestamptz structures. But at the same time, this also makes
MEOS somewhat coupled with postgres. I am wondering if this borrowing could
ever lead to any compatibility issues which a MEOS user might not expect?
Like for example could this lead to a situation where data
analyzed/processed with version X of MEOS only supports to be saved back
into say postgres versions of only version Y and above? Hopefully, however,
this should be a very rare situation as we only seem to borrow very base
level definitions which won't generally change and even the borrowed code
would be anyway be indirectly tested against all common use cases.

Thanks & Regards
Krishna

On Sat, 23 Jul 2022 at 04:17, Esteban Zimanyi <estebanzimanyi at gmail.com>
wrote:

> Dear Krishna
>
> We were able to finalize a first version of the MEOS library in the
> latest commit of the develop branch.
> https://github.com/estebanzimanyi/MobilityDB/commits/develop
>
> What is still missing is the timezone management. The reason for this
> is that PostgreSQL uses its own version of the standard files for
> timezones
>
> $ ls -l /usr/local/pgsql/14/share/timezone
> total 244
> drwxr-xr-x 2 root root 4096 May 10 20:17 Africa
> drwxr-xr-x 6 root root 4096 May 10 20:17 America
> drwxr-xr-x 2 root root 4096 May 10 20:17 Antarctica
> ...
>
> which is different from those of the underlying operating system,
> e.g., the files used in Linux
>
> $ ls -l /etc/localtime
> lrwxrwxrwx 1 root root 35 Jun 10 08:21 /etc/localtime ->
> /usr/share/zoneinfo/Europe/Brussels
>
> Both MySQL and Python use the standard timezone files
> https://docs.oracle.com/cd/E17952_01/mysql-8.0-en/time-zone-support.html
> https://docs.python.org/3/library/zoneinfo.html
>
> Our current approach in MEOS is to use the files of the operating
> systems. We will start this work from now on.
>
> We have also started writing a wiki page about the architecture
> enabling us to generate with the same codebase both MobilityDB and
> MEOS libraries.
> https://github.com/MobilityDB/MobilityDB/wiki/Building-MobilityDB-and-MEOS
>
> However, all the documentation of the MEOS library still needs to be
> written, as marked in the disclaimers of the web pages
> https://libmeos.org/
> We will work on it in the forthcoming weeks.
>
> The MobilityDB code has been thoroughly improved and tested, but the
> MEOS library is NOT yet ready, it is this commit that enables us to
> start working on it.
>
> We would appreciate any technical feedback you may have about this
> architecture.
>
> Best regards
>
> Esteban
>
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