ST_ClipByBox2D crashes backend

[strk]

I've found inputs that make ST_ClipByBox2D stuck, and attempts to interrupt it eventually crashes the backend.

It's some geometries in the gadm4 dataset. Those with cartodb_id=5 in the gadm4 test created as part of Windshaft-CartoDB tests.

This is probably a GEOS issue, anyway the symptom bubbles up here so I'm marking it as a blocker here (GEOS-3.5.0 isn't out yet)

[strk]

It actually seems to be a postgis issue, in that copying the offending input and using it as a literal fixes the problem, so it must have to do with memory management inside postgis.

The working query is:

SELECT ST_ClipByBox2d('0103000020110F00000100000008000000AA2120B4A7FB1241ECF43DA6E035524154CA0AA7A2FB1241E021BA67DD35524103868A5979FB1241A20C161ADC355241B9B52D4A3BFB12411890EA10DD3552416F3B80D811FB12418D1BAAA7DF355241C9C8206726FB1241C867BFE6E235524174D4D4B76EFB12415A4A8635E4355241AA2120B4A7FB1241ECF43DA6E0355241', 'BOX(-2661231.576776697 2348145.508920613,156543.033928043 5165920.119625353)'::box2d);

But if the geometry is retrived from a table, then it doesn't work anymore:

create table test (g geometry);
insert into test values ('0103000020110F00000100000008000000AA2120B4A7FB1241ECF43DA6E035524154CA0AA7A2FB1241E021BA67DD35524103868A5979FB1241A20C161ADC355241B9B52D4A3BFB12411890EA10DD3552416F3B80D811FB12418D1BAAA7DF355241C9C8206726FB1241C867BFE6E235524174D4D4B76EFB12415A4A8635E4355241AA2120B4A7FB1241ECF43DA6E0355241');
SELECT ST_ClipByBox2d(g, 'BOX(-2661231.576776697 2348145.508920613,156543.033928043 5165920.119625353)'::box2d) from test;

[strk]

Simpler case:

CREATE TEMPORARY TABLE t AS SELECT                                              
'POLYGON((41 20,41 0,21 0,1 20,1 40,21 40,41 20))'
::geometry g;                                                                   
SELECT ST_AsText(ST_ClipByBox2d(g, ST_MakeEnvelope(-20,-20,-10,-10))) FROM t;

[strk]

Got it, it's a wrong index passed to PG_FREE_IF_COPY :'( It's scary to realize such error is not catched by PostgreSQL at compile time…

[strk]

Fixed by r13028