MetadataStore updateObject API fails occasionally with a conditional check error.

The core of the updateObject API implementation is here.

In some rare cases (mostly observed when running a very high number of metadata only operations against the file system: e.g. restoring an HBase snapshot into a directory) this method will fail with a ConditionalCheck.

What seems to be happening is that an I/O error occurs, on the server side in DynamoDB the operation completes successfully and the client retries the operation (since from its perspective it failed with an I/O error). At this point the operation fails because it is issued with a ConditionalCheck which is not idempotent.

The proposed solution is to handle this particular case: when we receive a ConditionalCheck failed error we should read the state of the item from DynamoDB and check it against the item state that was received as an update. If the two are equal that means the operation was in fact executed successfully in DynamoDB and we should not raise the error up the call stack.

src/main/java/com/adobe/s3fs/metastore/internal/dynamodb/storage/AmazonDynamoDBStorage.java の updateObject 実装から始めます。大量のメタデータのみの操作中に、ConditionalCheck の失敗とクライアントの再試行がどのように処理されるかを追跡します。完了条件は、後続の DynamoDB 読み取りによって保存済みアイテムが要求された更新と一致することが示された場合にのみ、失敗した ConditionalCheck を抑制し、それ以外の場合はエラーが引き続き伝播されることです。