ExecuteQuerySegmentedAsync 与 ExecuteQuery 的 Azure 表查询限制

Question

调用ExecuteQuery()有哪些限制？例如，实体数量限制和下载大小。

也就是说，下面的方法什么时候会达到极限？

 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;
            }
        }

下面的方法是使用ExecuteQuerySegmentedAsync，TakeCount为50，但是50是如何确定的，我认为这是由我上面的问题决定的。

 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。这是基于 REST API 提出的限制，其中对表服务的单个请求最多可以返回 1000 个实体(引用:https://learn.microsoft.com/en-us/rest/api/storageservices/query-timeout-and-pagination)。

ExecuteQuery 方法将尝试返回与查询匹配的所有实体。在内部，它尝试在单次迭代中获取最多 1000 个实体，并且如果表服务的响应包含继续 token ，则将尝试获取下一组实体。

更新

If ExecuteQuery performs pagination automatically, it seems it is easier to use than ExecuteQuerySegmentedAsync. Why must I use ExecuteQuerySegmentedAsync? What about download size? 1000 entities regardless their sizes?

使用ExecuteQuery，您无法跳出循环。当表中有很多实体时，这会成为问题。通过 ExecuteQuerySegmentedAsync，您可以实现这种灵 active 。例如，假设您想要从一个非常大的表中下载所有实体并将它们保存在本地。如果您使用 ExecuteQuerySegmentedAsync，则可以将实体保存在不同的文件中。

关于您对 1000 个实体(无论大小)的评论，答案是肯定的。请记住，每个实体的最大大小可为 1MB。