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Oracle: after the tables grow and shrink, a labelled match with a property and an edge type finds nothing (wrong-results plan?)

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Una pull request collegata è già stata integrata.

  • #206 di @jasperblues — integrata

Valutazione

Difficoltà
5/5
Tempo stimato
Più di una settimana
Idoneità per principianti
24/100
Tipo di issue
Bug
Chiarezza
Abbastanza chiara
Stato di attività
Attiva
Stack tecnologico
python, sql
Ambito
backend, databases

Direzione di ricerca

Start by reproducing the issue with the Cypher spec followed by the heavy tests in the same Oracle session, then inspect the generated SQL and compare the executed plan using DISPLAY_CURSOR as a user with V$SESSION access. Try the issue's suggested checks: disable optimizer_adaptive_plans, gather statistics, and drop or rebuild the label index. Done means identifying a reproducible cause and confirming whether the proposed checks resolve the missing match; the issue also suggests checking drivine4j and drivine.

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

Descrizione

What happens: on Oracle, after a test session has run the Cypher spec (v0.6.1) and then written a hub of 2,500 and 5,000 relationships in the same tables, a labelled match with a property and a typed edge finds nothing, though the data is there:

MATCH (:Person {name: 'Keanu'})-[:KNOWS]->(p) RETURN p.name    -- []

When it fails, the store holds 9 nodes and 8 edges, Keanu KNOWS Carrie among them. These still find the row:

  • MATCH (a:Person)-[:KNOWS]->(p);
  • MATCH (a {name: 'Keanu'})-[:KNOWS]->(p).

(a:Person {name: 'Keanu'})-[r]->(p) finds nothing.

It's on main: main's compiler with the v0.6.1 spec copy and the heavy tests reproduced it in 2 of 2 runs in one session. Without the heavy tests, or without the spec run before them, it passes.

The SQL is plain and identical on main and on the batch-2 branch: drivine_node n1 CROSS JOIN drivine_node n2 CROSS JOIN drivine_edge e3, with n1's label JSON_EXISTS, JSON_QUERY(n1.props, '$.name') = JSON('"Keanu"'), e3.src = n1.nid, e3.dst = n2.nid and e3.type = 'KNOWS'.

EXPLAIN PLAN shows an adaptive plan with dynamic sampling at level 2: nested loops, a full scan of DRIVINE_EDGE filtered on type, DRIVINE_NODE by unique nid for n1 filtered on labels and name, then n2 by nid. Table statistics are NULL. The executed plan may differ; DISPLAY_CURSOR needs V$SESSION, which the test user lacks.

So this looks like an Oracle wrong-results plan, possibly with the multivalue label index or the adaptive plan, once the tables have grown and shrunk without statistics.

Next steps:

  • reproduce with DISPLAY_CURSOR as a user that can read V$SESSION;
  • try optimizer_adaptive_plans = FALSE, gathering statistics, and dropping or rebuilding the label index;
  • if it's an Oracle bug, report it with the minimal SQL;
  • check drivine4j and drivine (TypeScript) for the same, since they share the layout and the compiled SQL.

Found while porting Cypher batch 2 (drivine4j #206); that port works around it by writing its heavy tests' hub in a graph of its own.

Lingua principale
Python
Stelle
1
Fork
0
Merge medio
1h 19m
PR unite (30g)
122

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Come iniziare

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  4. Apri una pull request che faccia riferimento al numero della issue.

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