58d9acc18d
If convert_to_scalar is passed a pair of datatypes it can't cope with, its former behavior was just to elog(ERROR). While this is OK so far as the core code is concerned, there's extension code that would like to use scalarltsel/scalargtsel/etc as selectivity estimators for operators that work on non-core datatypes, and this behavior is a show-stopper for that use-case. If we simply allow convert_to_scalar to return FALSE instead of outright failing, then the main logic of scalarltsel/scalargtsel will work fine for any operator that behaves like a scalar inequality comparison. The lack of conversion capability will mean that we can't estimate to better than histogram-bin-width precision, since the code will effectively assume that the comparison constant falls at the middle of its bin. But that's still a lot better than nothing. (Someday we should provide a way for extension code to supply a custom version of convert_to_scalar, but today is not that day.) While poking at this issue, we noted that the existing code for handling type bytea in convert_to_scalar is several bricks shy of a load. It assumes without checking that if the comparison value is type bytea, the bounds values are too; in the worst case this could lead to a crash. It also fails to detoast the input values, so that the comparison result is complete garbage if any input is toasted out-of-line, compressed, or even just short-header. I'm not sure how often such cases actually occur --- the bounds values, at least, are probably safe since they are elements of an array and hence can't be toasted. But that doesn't make this code OK. Back-patch to all supported branches, partly because author requested that, but mostly because of the bytea bugs. The change in API for the exposed routine convert_network_to_scalar() is theoretically a back-patch hazard, but it seems pretty unlikely that any third-party code is calling that function directly. Tomas Vondra, with some adjustments by me Discussion: https://postgr.es/m/b68441b6-d18f-13ab-b43b-9a72188a4e02@2ndquadrant.com
The PostgreSQL contrib tree
---------------------------
This subtree contains porting tools, analysis utilities, and plug-in
features that are not part of the core PostgreSQL system, mainly
because they address a limited audience or are too experimental to be
part of the main source tree. This does not preclude their
usefulness.
User documentation for each module appears in the main SGML
documentation.
When building from the source distribution, these modules are not
built automatically, unless you build the "world" target. You can
also build and install them all by running "make all" and "make
install" in this directory; or to build and install just one selected
module, do the same in that module's subdirectory.
Some directories supply new user-defined functions, operators, or
types. To make use of one of these modules, after you have installed
the code you need to register the new SQL objects in the database
system by executing a CREATE EXTENSION command. In a fresh database,
you can simply do
CREATE EXTENSION module_name;
See the PostgreSQL documentation for more information about this
procedure.