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

Aperta
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Valutazione

Difficoltà
4/5
Tempo stimato
3-5 giorni
Idoneità per principianti
45/100
Tipo di issue
Bug
Chiarezza
Abbastanza chiara
Stato di attività
Attiva
Stack tecnologico
c, postgresql
Ambito
database, databases

Direzione di ricerca

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.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

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.

Lingua principale
C
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Merge medio
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PR unite (30g)
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