From dafd688d335d417c7c1e05418646000fb635d87f Mon Sep 17 00:00:00 2001 From: satyanarayana narlapuram Date: Tue, 21 Apr 2026 07:52:56 +0000 Subject: [PATCH v20260512 1/4] Prevent dropping the last label from a property graph element Per SQL/PGQ standard, every graph element must have at least one label. When dropping a label from a graph element, ensure that there exists at least one other label on the element. If the label being dropped is the only label on the element, raise an error. Add a test to make sure that dropping labels concurrently from the same element has the same effect. Reported By: Satyanarayana Narlapuram Author: Ashutosh Bapat Author: Satyanarayana Narlapuram Reviewed by: Ashutosh Bapat Discussion: https://www.postgresql.org/message-id/CAHg+QDeP=mTHTV48R23zKMy1SBmCKZ_L7-z5zKnYyw+K0x-gCg@mail.gmail.com --- doc/src/sgml/ref/alter_property_graph.sgml | 4 +- src/backend/commands/propgraphcmds.c | 54 +++++++++++++++++-- .../drop-propgraph-label-concurrently.out | 20 +++++++ src/test/isolation/isolation_schedule | 1 + .../drop-propgraph-label-concurrently.spec | 36 +++++++++++++ .../expected/create_property_graph.out | 6 +++ .../regress/sql/create_property_graph.sql | 4 ++ 7 files changed, 119 insertions(+), 6 deletions(-) create mode 100644 src/test/isolation/expected/drop-propgraph-label-concurrently.out create mode 100644 src/test/isolation/specs/drop-propgraph-label-concurrently.spec diff --git a/doc/src/sgml/ref/alter_property_graph.sgml b/doc/src/sgml/ref/alter_property_graph.sgml index f517f2b2d7a..2fd0c138e12 100644 --- a/doc/src/sgml/ref/alter_property_graph.sgml +++ b/doc/src/sgml/ref/alter_property_graph.sgml @@ -99,7 +99,9 @@ ALTER PROPERTY GRAPH [ IF EXISTS ] nameALTER {VERTEX|NODE|EDGE|RELATIONSHIP} TABLE ... DROP LABEL - This form removes a label from an existing vertex or edge table. + This form removes a label from an existing vertex or edge table. The + last label on an element table cannot be dropped; every vertex or edge + table must have at least one label. diff --git a/src/backend/commands/propgraphcmds.c b/src/backend/commands/propgraphcmds.c index cc516e27020..59b2f76ca4f 100644 --- a/src/backend/commands/propgraphcmds.c +++ b/src/backend/commands/propgraphcmds.c @@ -1491,8 +1491,14 @@ AlterPropGraph(ParseState *pstate, const AlterPropGraphStmt *stmt) { Oid peoid; Oid labeloid; - Oid ellabeloid; + Oid ellabeloid = InvalidOid; ObjectAddress obj; + Relation ellabelrel; + SysScanDesc ellabelscan; + ScanKeyData ellabelkey[1]; + int nlabels = 0; + HeapTuple tuple; + if (stmt->element_kind == PROPGRAPH_ELEMENT_KIND_VERTEX) peoid = get_vertex_oid(pstate, pgrelid, stmt->element_alias, -1); @@ -1510,11 +1516,38 @@ AlterPropGraph(ParseState *pstate, const AlterPropGraphStmt *stmt) get_rel_name(pgrelid), stmt->element_alias, stmt->drop_label), parser_errposition(pstate, -1)); - ellabeloid = GetSysCacheOid2(PROPGRAPHELEMENTLABELELEMENTLABEL, - Anum_pg_propgraph_element_label_oid, - ObjectIdGetDatum(peoid), - ObjectIdGetDatum(labeloid)); + /* + * Is the given label associated with the element? Is this the only + * label associated with the element? + */ + ellabelrel = table_open(PropgraphElementLabelRelationId, AccessShareLock); + ScanKeyInit(&ellabelkey[0], + Anum_pg_propgraph_element_label_pgelelid, + BTEqualStrategyNumber, F_OIDEQ, + ObjectIdGetDatum(peoid)); + ellabelscan = systable_beginscan(ellabelrel, PropgraphElementLabelElementLabelIndexId, + true, NULL, 1, ellabelkey); + while (HeapTupleIsValid(tuple = systable_getnext(ellabelscan))) + { + Form_pg_propgraph_element_label ellabelform = (Form_pg_propgraph_element_label) GETSTRUCT(tuple); + + nlabels++; + if (ellabelform->pgellabelid == labeloid) + ellabeloid = ellabelform->oid; + + /* + * If we find more than one label associated with the given + * element and also found the label we are going to drop, we are + * done. + */ + if (nlabels > 1 && ellabeloid) + break; + } + systable_endscan(ellabelscan); + table_close(ellabelrel, AccessShareLock); + + /* Given label is not associated with the element. */ if (!ellabeloid) ereport(ERROR, errcode(ERRCODE_UNDEFINED_OBJECT), @@ -1522,6 +1555,17 @@ AlterPropGraph(ParseState *pstate, const AlterPropGraphStmt *stmt) get_rel_name(pgrelid), stmt->element_alias, stmt->drop_label), parser_errposition(pstate, -1)); + /* + * Prevent dropping the last label from an element. Every element must + * have at least one label. + */ + if (nlabels == 1) + ereport(ERROR, + (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE), + errmsg("cannot drop the last label from element \"%s\"", + stmt->element_alias), + errhint("Every element must have at least one label."))); + ObjectAddressSet(obj, PropgraphElementLabelRelationId, ellabeloid); performDeletion(&obj, stmt->drop_behavior, 0); diff --git a/src/test/isolation/expected/drop-propgraph-label-concurrently.out b/src/test/isolation/expected/drop-propgraph-label-concurrently.out new file mode 100644 index 00000000000..a3fc89fbac1 --- /dev/null +++ b/src/test/isolation/expected/drop-propgraph-label-concurrently.out @@ -0,0 +1,20 @@ +Parsed test spec with 2 sessions + +starting permutation: s1b s1drop1 s2b s2drop2 s1c s2c +step s1b: BEGIN; +step s1drop1: ALTER PROPERTY GRAPH pgg1 ALTER VERTEX TABLE pgt1 DROP LABEL pgl1; +step s2b: BEGIN; +step s2drop2: ALTER PROPERTY GRAPH pgg1 ALTER VERTEX TABLE pgt1 DROP LABEL pgl2; +step s1c: COMMIT; +step s2drop2: <... completed> +ERROR: cannot drop the last label from element "pgt1" +step s2c: COMMIT; + +starting permutation: s1b s1drop1 s2b s2drop2 s1r s2c +step s1b: BEGIN; +step s1drop1: ALTER PROPERTY GRAPH pgg1 ALTER VERTEX TABLE pgt1 DROP LABEL pgl1; +step s2b: BEGIN; +step s2drop2: ALTER PROPERTY GRAPH pgg1 ALTER VERTEX TABLE pgt1 DROP LABEL pgl2; +step s1r: ROLLBACK; +step s2drop2: <... completed> +step s2c: COMMIT; diff --git a/src/test/isolation/isolation_schedule b/src/test/isolation/isolation_schedule index 1578ba191c8..9c64ee43641 100644 --- a/src/test/isolation/isolation_schedule +++ b/src/test/isolation/isolation_schedule @@ -126,3 +126,4 @@ test: serializable-parallel-3 test: matview-write-skew test: lock-nowait test: for-portion-of +test: drop-propgraph-label-concurrently diff --git a/src/test/isolation/specs/drop-propgraph-label-concurrently.spec b/src/test/isolation/specs/drop-propgraph-label-concurrently.spec new file mode 100644 index 00000000000..ce8f4351364 --- /dev/null +++ b/src/test/isolation/specs/drop-propgraph-label-concurrently.spec @@ -0,0 +1,36 @@ +# ALTER PROPERTY GRAPH ... DROP LABEL - concurrent +# +# Verify that two concurrent transactions cannot both drop a label from +# the same element such that the element ends up with no labels. + +setup +{ + CREATE TABLE pgt1 (a int, b int); + CREATE PROPERTY GRAPH pgg1 + VERTEX TABLES (pgt1 KEY (a) + LABEL pgl1 PROPERTIES (b) + LABEL pgl2 PROPERTIES (a, b)); +} + +teardown +{ + DROP PROPERTY GRAPH IF EXISTS pgg1; + DROP TABLE pgt1; +} + +session s1 +step s1b { BEGIN; } +step s1drop1 { ALTER PROPERTY GRAPH pgg1 ALTER VERTEX TABLE pgt1 DROP LABEL pgl1; } +step s1c { COMMIT; } +step s1r { ROLLBACK; } + +session s2 +step s2b { BEGIN; } +step s2drop2 { ALTER PROPERTY GRAPH pgg1 ALTER VERTEX TABLE pgt1 DROP LABEL pgl2; } +step s2c { COMMIT; } + +# s2drop2 fails since by then pgl2 is the only remaining label on pgt1 +permutation s1b s1drop1 s2b s2drop2 s1c s2c + +# s2drop2 succeeds since rollback leaves pgl1 behind +permutation s1b s1drop1 s2b s2drop2 s1r s2c diff --git a/src/test/regress/expected/create_property_graph.out b/src/test/regress/expected/create_property_graph.out index f625524abce..dd6c67167e5 100644 --- a/src/test/regress/expected/create_property_graph.out +++ b/src/test/regress/expected/create_property_graph.out @@ -57,6 +57,12 @@ ALTER PROPERTY GRAPH g3 ALTER PROPERTY GRAPH g3 ALTER VERTEX TABLE t3 DROP LABEL t3l3x; -- error ERROR: property graph "g3" element "t3" has no label "t3l3x" ALTER PROPERTY GRAPH g3 ALTER VERTEX TABLE t3 DROP LABEL t3l3; +-- Test that the last label on an element cannot be dropped +ALTER PROPERTY GRAPH g3 ALTER VERTEX TABLE t3 DROP LABEL t3l2; +ALTER PROPERTY GRAPH g3 ALTER VERTEX TABLE t3 DROP LABEL t3l1; -- error: last label +ERROR: cannot drop the last label from element "t3" +HINT: Every element must have at least one label. +ALTER PROPERTY GRAPH g3 ALTER VERTEX TABLE t3 ADD LABEL t3l2 PROPERTIES ALL COLUMNS; ALTER PROPERTY GRAPH g3 DROP VERTEX TABLES (t2); -- fail ERROR: cannot drop vertex t2 of property graph g3 because other objects depend on it DETAIL: edge e1 of property graph g3 depends on vertex t2 of property graph g3 diff --git a/src/test/regress/sql/create_property_graph.sql b/src/test/regress/sql/create_property_graph.sql index 241f93df302..4cf771596a8 100644 --- a/src/test/regress/sql/create_property_graph.sql +++ b/src/test/regress/sql/create_property_graph.sql @@ -52,6 +52,10 @@ ALTER PROPERTY GRAPH g3 ADD LABEL t3l3 PROPERTIES ALL COLUMNS; ALTER PROPERTY GRAPH g3 ALTER VERTEX TABLE t3 DROP LABEL t3l3x; -- error ALTER PROPERTY GRAPH g3 ALTER VERTEX TABLE t3 DROP LABEL t3l3; +-- Test that the last label on an element cannot be dropped +ALTER PROPERTY GRAPH g3 ALTER VERTEX TABLE t3 DROP LABEL t3l2; +ALTER PROPERTY GRAPH g3 ALTER VERTEX TABLE t3 DROP LABEL t3l1; -- error: last label +ALTER PROPERTY GRAPH g3 ALTER VERTEX TABLE t3 ADD LABEL t3l2 PROPERTIES ALL COLUMNS; ALTER PROPERTY GRAPH g3 DROP VERTEX TABLES (t2); -- fail ALTER PROPERTY GRAPH g3 DROP VERTEX TABLES (t2) CASCADE; ALTER PROPERTY GRAPH g3 DROP EDGE TABLES (e2); base-commit: 8268e41aca23ae3414360b0a1dc6ae99ea7b43f4 -- 2.34.1