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Cassandra: an unavailable replica set is reported as a 500 storage fault rather than a retryable 503

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#593 0 comentarios 0 reacciones 0 asignados Ver en GitHub

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Evaluación

Dificultad
3/5
Tiempo estimado
1-2 días
Aptitud para principiantes
70/100
Tipo de issue
Error
Claridad
Bien especificado
Estado de actividad
Activo
Stack tecnológico
cassandra, rust
Área
backend, database

Línea de trabajo

Start with the map_err sites in crates/storage-cassandra/src/cassandra_util.rs and the Database error mappings in data/delete_item.rs and data/transactions.rs; read crates/storage/src/error.rs to understand StorageError::Transient. Check how the Cassandra driver represents unavailable replicas and exhausted query plans. Done when these failures map to the retryable storage error, while delete and transaction logs retain the driver's error details.

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

Descripción

backend:cassandra

Summary

Every Cassandra driver error on the data path is wrapped as StorageError::Internal and reaches the client as HTTP 500 InternalServerError. Since #591 (the fix for #560), a ConsistentRead: true read, an export or an item write that cannot reach a local quorum of replicas fails this way. The repository's class for a failure that succeeds on retry is StorageError::Transient, which the engine maps to 503 ServiceUnavailable, the status the SDKs retry.

Observed

On a keyspace at replication factor 3 with one replica up:

  • GetItem with ConsistentRead: true: 500, log Get item: General error: No nodes available in query plan! (one node; the driver retried the unavailable read once and found no next node) or Cannot achieve consistency level LOCAL_QUORUM with UnavailableError { cl: LocalQuorum, required: 2, alive: 1 } (a cluster).
  • PutItem, UpdateItem: 500 with the same texts prefixed by put_item read: or occ_read:.
  • DeleteItem of an existing item and TransactWriteItems: 500 with the text Database error, which names neither the level nor the replica counts (admin_store.rs and metadata_engine.rs produce the literal; the two data paths that return it were not traced).

Expected

The driver's Unavailable error, and the No nodes available in query plan! that follows a retried Unavailable, map to StorageError::Transient, so the client receives 503 and the SDK retries. The DeleteItem and TransactWriteItems mappings carry the driver's text so the log names the level and the replica counts.

Where

  • crates/storage-cassandra/src/cassandra_util.rs (the map_err sites in execute_at, query_rows_at, query_optional_at, query_lwt)
  • crates/storage-cassandra/src/data/delete_item.rs, data/transactions.rs (the Database error mappings)
  • crates/storage/src/error.rs (StorageError::Transient)
Lenguaje dominante
Rust
Estrellas
517
Forks
60
Merge medio
2 d 22 h
PR fusionados (30 d)
25

Preparar el entorno

Primeros pasos

  1. Lee el issue completo y luego la guía de contribución del proyecto.
  2. Comenta en el issue que vas a ocuparte — evita que dos personas hagan lo mismo.
  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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