Previously, on most platforms, we allowed hstore_plpython's references
to hstore and plpython to be unresolved symbols at link time, trusting
the dynamic linker to resolve them when the module is loaded. This
has a number of problems, the worst being that the dynamic linker
does not know where the references come from and can do nothing but
fail if those other modules haven't been loaded. We've more or less
gotten away with that for the limited use-case of datatype transform
modules, but even there, it requires some awkward hacks, most recently
commit 83c249200.
Instead, let's not treat these references as linker-resolvable at all,
but use function pointers that are manually filled in by the module's
_PG_init function. There are few enough contact points that this
doesn't seem unmaintainable, at least for these use-cases. (Note that
the same technique wouldn't work at all for decoupling from libpython
itself, but fortunately that's just a standard shared library and can
be linked to normally.)
This is an initial patch that just converts hstore_plpython. If the
buildfarm doesn't find any fatal problems, I'll work on the other
transform modules soon.
Tom Lane, per an idea of Andres Freund's.
Discussion: <2652.1475512158@sss.pgh.pa.us>
Extension scripts should never use CREATE OR REPLACE for initial object
creation. If there is a collision with a pre-existing (probably
user-created) object, we want extension installation to fail, not silently
overwrite the user's object. Bloom and sslinfo both violated this precept.
Also fix a number of scripts that had no standard header (the file name
comment and the \echo...\quit guard). Probably the \echo...\quit hack
is less important now than it was in 9.1 days, but that doesn't mean
that individual extensions get to choose whether to use it or not.
And fix a couple of evident copy-and-pasteos in file name comments.
No need for back-patch: the REPLACE bugs are both new in 9.6, and the
rest of this is pretty much cosmetic.
Andreas Karlsson and Tom Lane
Commit 866566a690 is insufficient to prevent dump/reload failures
when using transform modules in a database with both plpython2 and
plpython3 installed. The reason is that the transform extension scripts
use DO blocks as a mechanism to pull in the libpython library before
creating the transform function. It's necessary to preload the library
because the dynamic loader won't do it for us on every platform, leading
to "unresolved symbol" failures when the transform library is loaded.
But it's *not* necessary to execute Python code, and doing so will
provoke a multiple-Pythons-are-loaded error even after the preceding
commit.
To fix, use LOAD instead of a DO block. That requires superuser privilege,
but creation of a C function does anyway. It also embeds knowledge of
the underlying library name for each PL language; but that's wired into
the initdb-time contents of pg_pltemplate too, so that doesn't seem like
a large problem either. Note that CREATE TRANSFORM as such doesn't call
the language module at all.
Per a report from Paul Jones. Back-patch to 9.5 where transform modules
were introduced.
This provides a mechanism for specifying conversions between SQL data
types and procedural languages. As examples, there are transforms
for hstore and ltree for PL/Perl and PL/Python.
reviews by Pavel Stěhule and Andres Freund
Tom Lane
Peter Eisentraut