具有ExecuteQuerySegmentedAsync与ExecuteQuery的Azure表查询限制

Question

调用ExecuteQuery()的限制是什么？例如，实体数限制和下载大小。

换句话说，下面的方法何时会达到其极限？

 private static void ExecuteSimpleQuery(CloudTable table, string partitionKey, string startRowKey, string endRowKey)
        {
            try
            {
                // Create the range query using the fluid API 
                TableQuery<CustomerEntity> rangeQuery = new TableQuery<CustomerEntity>().Where(
                    TableQuery.CombineFilters(
                            TableQuery.GenerateFilterCondition("PartitionKey", QueryComparisons.Equal, partitionKey),
                            TableOperators.And,
                            TableQuery.CombineFilters(
                                TableQuery.GenerateFilterCondition("RowKey", QueryComparisons.GreaterThanOrEqual, startRowKey),
                                TableOperators.And,
                                TableQuery.GenerateFilterCondition("RowKey", QueryComparisons.LessThanOrEqual, endRowKey))));

                foreach (CustomerEntity entity in table.ExecuteQuery(rangeQuery))
                {
                    Console.WriteLine("Customer: {0},{1}\t{2}\t{3}", entity.PartitionKey, entity.RowKey, entity.Email, entity.PhoneNumber);
                }
            }
            catch (StorageException e)
            {
                Console.WriteLine(e.Message);
                Console.ReadLine();
                throw;
            }
        }

下面的方法使用ExecuteQuerySegmentedAsync的TakeCount为50，但是如何确定50，这是我上面的问题所确定的。

 private static async Task PartitionRangeQueryAsync(CloudTable table, string partitionKey, string startRowKey, string endRowKey)
        {
            try
            {
                // Create the range query using the fluid API 
                TableQuery<CustomerEntity> rangeQuery = new TableQuery<CustomerEntity>().Where(
                    TableQuery.CombineFilters(
                            TableQuery.GenerateFilterCondition("PartitionKey", QueryComparisons.Equal, partitionKey),
                            TableOperators.And,
                            TableQuery.CombineFilters(
                                TableQuery.GenerateFilterCondition("RowKey", QueryComparisons.GreaterThanOrEqual, startRowKey),
                                TableOperators.And,
                                TableQuery.GenerateFilterCondition("RowKey", QueryComparisons.LessThanOrEqual, endRowKey))));

                // Request 50 results at a time from the server. 
                TableContinuationToken token = null;
                rangeQuery.TakeCount = 50;
                int segmentNumber = 0;
                do
                {
                    // Execute the query, passing in the continuation token.
                    // The first time this method is called, the continuation token is null. If there are more results, the call
                    // populates the continuation token for use in the next call.
                    TableQuerySegment<CustomerEntity> segment = await table.ExecuteQuerySegmentedAsync(rangeQuery, token);

                    // Indicate which segment is being displayed
                    if (segment.Results.Count > 0)
                    {
                        segmentNumber++;
                        Console.WriteLine();
                        Console.WriteLine("Segment {0}", segmentNumber);
                    }

                    // Save the continuation token for the next call to ExecuteQuerySegmentedAsync
                    token = segment.ContinuationToken;

                    // Write out the properties for each entity returned.
                    foreach (CustomerEntity entity in segment)
                    {
                        Console.WriteLine("\t Customer: {0},{1}\t{2}\t{3}", entity.PartitionKey, entity.RowKey, entity.Email, entity.PhoneNumber);
                    }

                    Console.WriteLine();
                }
                while (token != null);
            }
            catch (StorageException e)
            {
                Console.WriteLine(e.Message);
                Console.ReadLine();
                throw;
            }
        }

示例来自以下链接：https://github.com/Azure-Samples/storage-table-dotnet-getting-started

Answer 1

对于ExecuteQuerySegmentedAsync，限制为1000。这基于REST API的限制，其中对表服务的单个请求最多可以返回1000个实体（参考：https://docs.microsoft.com/en-us/rest/api/storageservices/query-timeout-and-pagination）。

ExecuteQuery方法将尝试返回所有与查询匹配的实体。在内部，它尝试在一次迭代中最多获取1000个实体，并且如果表服务的响应中包含延续令牌，则将尝试获取下一组实体。

UPDATE

如果ExecuteQuery自动执行分页，似乎是比ExecuteQuerySegmentedAsync更易于使用。我为什么要用ExecuteQuerySegmentedAsync？那下载大小呢？ 1000个实体不论大小？

使用ExecuteQuery，您将无法摆脱循环。当表中有很多实体时，这将成为问题。您可以通过ExecuteQuerySegmentedAsync拥有这种灵活性。例如，假设您要从一个很大的表中下载所有实体并将其保存在本地。如果使用ExecuteQuerySegmentedAsync，则可以将实体保存在不同的文件中。

关于您对1000个实体的评论，无论其大小如何，答案是肯定的。请记住，每个实体的最大大小为1MB。