) and have some questions about versioning. First of all, I have to say that the versioning system on the sql side is wonderful. It's really simple to write migrations etc.
However when thinking through the implications of having a database cluster with databases having different extension versions installed, it was not apparently clear to me how to synchronize the installed extension version with a shared library version. For example, if I have timescaledb version 0.1.0 in one db and version 0.2.0 in another db, I'd like for
timescaledb-0.1.0.so and
timescaledb-0.2.0.so to be used, respectively. (I want to avoid having to keep backwards-compatibility for all functions in future shared-libraries). In our case, this is further complicated by the fact that we need to preload the shared library since we are accessing the planner hooks etc. Below, I'll describe some solutions I have been thinking about, but wanted to hear if anyone else on this list has already solved this problem and has some insight. It is also quite possible I am missing something.
Issue 1: Preloading the right shared library.
When preloading libraries (either via local_preload_libraries, or session_preload_libraries, shared_preload_libraries), it would be nice to preload the shared_library according to it's version. But, I looked through the code and found no logic for adding version numbers to shared library names.
Solution 1: Set session_preload_libraries on the database via ALTER DATABASE SET. This can be done in the sql and the sql version-migration scripts can change this value as you change extensions versions. I think this would work, but it seems very hack-ish and less-than-ideal.
Solution 2: Create some kind of stub shared-library that will, in turn, load another shared library of the correct version. This seems like the cleaner approach. Has anybody seen/implemented something like this already?
Issue 2: module_pathname
I believe that for user defined function the MODULE_PATHNAME substitution will not work since that setting is set once per-extension. Thus, for example, the migration scripts that include function definitions for older versions would use the latest .so file if MODULE_PATHNAME was used in the definition. This would be a problem if upgrading to an intermediate (not latest) version.
Solution: MODULE_PATHNAME cannot be used, and we should build our own templating/makefile infrastructure to link files to the right-versioned shared library in the CREATE FUNCTION definition.