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AGE lets a later `MERGE` feed a node into an earlier unrestricted `MATCH` scan

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Evaluación

Dificultad
4/5
Tiempo estimado
3-5 días
Aptitud para principiantes
45/100
Tipo de issue
Error
Claridad
Bastante claro
Estado de actividad
Activo
Stack tecnológico
c, postgresql
Área
database, databases

Línea de trabajo

Start by tracing how AGE plans and executes MATCH scans when later clauses such as DETACH DELETE and MERGE write to the same graph; the reproduction compares a direct query with one that materializes the earlier rows through collect and UNWIND. Find the relevant planner or executor code and tests for clause composition, then add coverage for both queries. Done means both return 2 rows on the reported environment.

Escrito por el modelo de indexación a partir del texto del issue.

Descripción

bug

Environment

  • Apache AGE 1.8.0, PostgreSQL 18.6
  • Docker image: apache/age:release_PG18_1.8.0

Reproduction

Create two initially unlabeled nodes in each of two clean graphs:

LOAD 'age';
SET search_path = ag_catalog, public;

SELECT ag_catalog.create_graph('age_repro24_left');
SELECT *
FROM ag_catalog.cypher('age_repro24_left', $$
CREATE (), ()
$$) AS (v agtype);

SELECT ag_catalog.create_graph('age_repro24_right');
SELECT *
FROM ag_catalog.cypher('age_repro24_right', $$
CREATE (), ()
$$) AS (v agtype);
Baseline — age_repro24_left
SELECT *
FROM ag_catalog.cypher('age_repro24_left', $$
MATCH (n)
DETACH DELETE n
MERGE (:New)
RETURN count(*) AS rows
$$) AS (rows agtype);
Row-materialized variant — age_repro24_right
SELECT *
FROM ag_catalog.cypher('age_repro24_right', $$
MATCH (n)
WITH {n: n} AS row
WITH collect(row) AS rows
UNWIND rows AS row
WITH row.n AS n
DETACH DELETE n
MERGE (:New)
RETURN count(*) AS rows
$$) AS (rows agtype);

The collect/UNWIND block preserves the two input rows and their bindings;
it materializes the earlier MATCH result before the later writes.

Expected and actual

The initial MATCH should bind the two nodes that exist when that clause is
evaluated. The later MERGE must not add another row to that already-completed
scan. Both queries should therefore return 2.

On AGE 1.8.0 / PostgreSQL 18.6:

baseline: 3 rows
barrier:  2 rows

The official Cypher clause-composition documentation states that a clause
cannot observe writes made by a later clause and notes that a MATCH before
CREATE does not find the node created later in the query: Neo4j Cypher
clause composition.

Lenguaje dominante
C
Estrellas
4.9k
Forks
535
Merge medio
10 d 13 h
PR fusionados (30 d)
7

Preparar el entorno

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  3. Haz un fork del repositorio y trabaja en una rama.
  4. Abre un pull request que haga referencia al número del issue.

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