Based on my experience with the 7.1.3 user defined type API, here are
several wishlist items. (They don't seem to be in 7.2b4 either.)
1) load/unload functions
Some user-defined types and functions require initialization of
global structures. This can be handled by code like
static int initialize() { static int initialized = 0;
if (!initialized) { //... do global initialization initialized = 1; } }
but this requires that every user-defined function call this
routine.
But more importantly, there's no way to free resources when the
database shuts down or loads the shared library. A memory leak may
be acceptable, but it's not acceptable for physical or virtual devices
to remain locked.
Proposed solution: define a new data structure that contains
information about the user-defined types/function module. This
structure would contain routines that are called when the shared
library is loaded or unloaded. Something like:
typedef struct { char *name; int (*load)(); // returns nonzero on error int (*unload)(); ... }
PG_USER_TYPE_INFO;
2) autoconfiguring functions
It should be possible for a user-defined type to define itself,
perhaps via a "bootstrap" procedure in the structure mentioned
above. The bootstrap procedure could use SPI calls to define
its own types, functions, operators and secondary indexes.
All but the last item can be done by a SQL script, of course,
but this provides a cleaner mechanism for complex packages.
(My libpkixpq script, for instance, is over 1000 lines long!)
This function would probably take one or two single arguments,
the path to the shared library being bootstrapped and possibly
the name of the database
3) context information
The final wishlist item, which may not be doable, is to have
some context for the query. I know that the fcinfo structure
does have a "context" field, but what I would really like to
have is a clean way to determine:
1) the current database
2) the target relation, or NULL if it's a freestanding select clause.
The purpose is to allow the user-defined functions to pull out
metadata maintained elsewhere. E.g., I might define a catalogue
containing public encryption encryption keys to use when writing
data into certain tables. My encryption routines could pull this
information out of the database with SPI... if I knew the name of
the table that was the target of the insert or update.
