Hi hackers,
ALTER PROPERTY GRAPH ... ALTER ... DROP LABEL currently allows removing
the last label from an element, leaving it with zero labels.
On assert-enabled builds, pg_get_propgraphdef() hits
TRAP: failed Assert("count > 0"), File: "ruleutils.c", Line: 1837, PID: 1821840
Repro:
CREATE TABLE t (x int PRIMARY KEY, y int, z int);
CREATE PROPERTY GRAPH g VERTEX TABLES (t KEY (x) LABEL l1 LABEL l2);
ALTER PROPERTY GRAPH g ALTER VERTEX TABLE t DROP LABEL l2;
ALTER PROPERTY GRAPH g ALTER VERTEX TABLE t DROP LABEL l1;
SELECT pg_get_propgraphdef('g'::regclass);
We can fix it two ways, (1) Prevent dropping the last label; (2) handle zero labels.
I feel it is easier to prevent dropping the last label than handling zero labels. Thoughts?
The attached patch adds a check in AlterPropGraph() before
performDeletion(). It scans pg_propgraph_element_label to count labels
for the element, and raises an error if only one remains. A regression test is included
that drops labels down to the last one, verifies the error, then re-adds them back.
Thanks,
Satya
