如何在Azure Cosmos DB（表API）上调试/排除元数据DTU限制？

Question

我们使用Azure cosmos DB来保存作业处理管道的状态信息。为此，我们使用了table API和相应的SDK。最近，我们注意到系统频繁运行到429——请求率误差太大。我们的事务性DTU利用率远低于表上配置的最大值，但是我们注意到在metrics选项卡下，系统dtu被枚举表等操作使用..被耗尽，因此429。

我们删除“CreateIfNotExists”方法调用的初始修复程序帮助修复了一段时间，但最近我们又开始遇到这个问题（尽管不像以前那么频繁）。很难对此进行调试/故障排除，因为在那里我找不到足够的文档，说明哪个SDK方法调用耗尽了这个不可扩展的资源。我已在 CosmosDB 实例上启用日志记录，但我不确定在日志中查找什么来解决此问题

这是我们用于与Azure Cosmos DB接口的单例类

public class CosmosDbTableFacade : ICosmosDbTableFacade
{
        /// <summary>
        /// Initializes a new instance of the <see cref="CosmosDbTableFacade"/> class.
        /// </summary>
        /// <param name="connectionString">
        /// The connection string.
        /// </param>
        /// <param name="tableName">
        /// The table name.
        /// </param>
        public CosmosDbTableFacade(string connectionString)
        {
            var storageAccount = CloudStorageAccount.Parse(connectionString);
            this.CosmosTableClient = storageAccount.CreateCloudTableClient();
        }

        /// <summary>
        /// Gets or sets the cosmos table.
        /// </summary>
        public CloudTableClient CosmosTableClient { get; set; }

        /// <summary>
        /// The execute async.
        /// </summary>
        /// <param name="tableName">
        /// The table Name.
        /// </param>
        /// <param name="operation">
        /// The operation.
        /// </param>
        /// <returns>
        /// The <see cref="Task"/>.
        /// </returns>
        public Task<TableResult> ExecuteAsync(string tableName, TableOperation operation)
        {
            var table = this.CosmosTableClient.GetTableReference(tableName);
            return table.ExecuteAsync(operation);
        }

        /// <summary>
        /// The execute query segmented async.
        /// </summary>
        /// <param name="tableName">
        /// The table name.
        /// </param>
        /// <param name="query">
        /// The query.
        /// </param>
        /// <param name="continuationToken">
        /// The continuation token.
        /// </param>
        /// <returns>
        /// The <see cref="Task"/> which returns the list of entities.
        /// </returns>
        public Task<TableQuerySegment<DynamicTableEntity>> ExecuteQuerySegmentedAsync(string tableName, TableQuery query, TableContinuationToken continuationToken)
        {
            var table = this.CosmosTableClient.GetTableReference(tableName);
            return table.ExecuteQuerySegmentedAsync(query, continuationToken);
        }
}

以下片段列出了我们正在使用的不同查询-

public async Task InsertOrMergeEntityAsync<T>(string tableName, T entity)
            where T : TableEntity
{
            var insertOrMergeOperation = TableOperation.InsertOrMerge(entity);
            var result = await this.CosmosDbTableFacade.ExecuteAsync(tableName, insertOrMergeOperation).ConfigureAwait(false);
            ValidateCosmosTableResult(result, "Failed to write to Cosmos Table");
}

public async Task<T> GetEntityAsync<T>(string tableName, string partitionKey, string rowKey)
            where T : TableEntity
{
            var retrieveOperation = TableOperation.Retrieve<T>(partitionKey, rowKey);
            TableResult result = await this.CosmosDbTableFacade.ExecuteAsync(tableName, retrieveOperation).ConfigureAwait(false);
            ValidateCosmosTableResult(result, "Failed to read from Cosmos Table");
            return result.Result as T;
}

public async Task<IEnumerable<T>> GetEntitiesAsync<T>(string tableName, string filterCondition)
            where T : TableEntity
{
            var query = new TableQuery().Where(filterCondition);
            var continuationToken = default(TableContinuationToken);
            var results = new List<T>();
            do
            {
                var currentQueryResults = await this.CosmosDbTableFacade.ExecuteQuerySegmentedAsync(tableName, query, continuationToken).ConfigureAwait(false);
                results.AddRange(currentQueryResults.Select(currentQueryResult =>
                    {
                        var currentEntity = TableEntity.ConvertBack<T>(currentQueryResult.Properties, null);
                        currentEntity.RowKey = currentQueryResult.RowKey;
                        currentEntity.PartitionKey = currentQueryResult.PartitionKey;
                        currentEntity.Timestamp = currentQueryResult.Timestamp;
                        currentEntity.ETag = currentQueryResult.ETag;
                        return currentEntity;
                    }));
                continuationToken = currentQueryResults.ContinuationToken;
            }
            while (continuationToken != null);

            return results;
}

下面最后一个方法中的筛选器包含分区键和自定义列

Answer 1

对于遇到类似问题的人来说，在我的例子中，元数据DTU限制的根本原因是：GetTableReference（tableName）方法（通过部署将该行移动到启动代码并监视DTU利用率的更改来找到）。我有这个，以便我可以在运行时动态指向要读/写到哪个表，但由于这会消耗元数据DTU，因此我将代码更改为使用单例作为表引用。