Hi all,
I’m trying to implement an spgist index in the PostGIS extension, which seems like it should work, but is thus far not
workingfor what appear (to me) to be issues in the way spgist expects to pass pointers to user-defined functions.
Right before anything happens, spgist calls a ‘config’ routine in the user code. This is the code from the example
implementation(which is internal to pgsql, not a run-time add-on like postgis)
Datum
spg_quad_config(PG_FUNCTION_ARGS)
{
/* spgConfigIn *cfgin = (spgConfigIn *) PG_GETARG_POINTER(0); */
spgConfigOut *cfg = (spgConfigOut *) PG_GETARG_POINTER(1);
cfg->prefixType = POINTOID;
cfg->labelType = VOIDOID; /* we don't need node labels */
cfg->canReturnData = true;
cfg->longValuesOK = false;
PG_RETURN_VOID();
}
It is called from the spgist core in the spgGetCache() function, via
FunctionCall2Coll(procinfo,
index->rd_indcollation[0],
PointerGetDatum(&in),
PointerGetDatum(&cache->config));
The part the user function cares about is the pointer to cache->config.
In the core code, the call stack to the user function goes like this:
postgres`spg_quad_config(fcinfo=0x00007fff5f0faf90) + 18 at spgquadtreeproc.c:29
postgres`FunctionCall2Coll(flinfo=0x00007ff59a804cc8, collation=0, arg1=140734788252568, arg2=140692835814944) + 150 at
fmgr.c:1327
postgres`spgGetCache(index=0x000000010254be68) + 220 at spgutils.c:71
So, spgGetCache to FunctionCall2Coll to spg_quad_config.
In my user-defined version of the same thing (I just copied the C code and wrote a CREATE OPERATOR CLASS for it) the
callstack is this
postgis-2.2.so`gserialized_spgist_quadtree_2d_config(fcinfo=0x00007fff5f0fb398) + 30 at gserialized_spgist_2d.c:60
postgres`fmgr_oldstyle(fcinfo=0x00007fff5f0faf90) + 424 at fmgr.c:678
postgres`FunctionCall2Coll(flinfo=0x00007ff59a039cc8, collation=0, arg1=140734788252568, arg2=140692827643424) + 150 at
fmgr.c:1327
postgres`spgGetCache(index=0x000000010254be68) + 220 at spgutils.c:71
So, spgGetCache to FunctionCall2Coll to fmgr_oldstyle to
gserialized_spgist_quadtree_2d_config!
On the way through fmgr_oldstyle things go very much awry and the gserialized_spgist_quadtree_2d_config doesn’t get
calledwith a pointer to an fcinfo, but with a pointer to the block of memory occupied by the first argument, and from
therethings naturally stop working.
So, I’m wondering what I could have done that is causing my calls to route through fmgr_oldstyle instead of the usual
path?
P.
--
Paul Ramsey
http://cleverelephant.ca
http://postgis.net
