pick from master #36316
expression cast( xx as decimal )'s datatype maybe decimalv3 or decimalv2
depending on enable_decimal_conversion value in fe conf file. if
enable_decimal_conversion is true, the datatype is decimalv3(9, 0), but
the datatype was decimalv3(38, 9) in 2.0 releases. So this pr change the
datatype same as 2.0 releases to keep the behavior consistent.
* (feature)(cloud) Use dynamic allocator instead of static buffer pool for better elasticity. (#28983)
* [fix](outfile) Fix unable to export empty data (#30703)
Issue Number: close#30600
Fix unable to export empty data to hdfs / S3, this behavior is inconsistent with version 1.2.7,
version 1.2.7 can export empty data to hdfs/ S3, and there will be exported files on S3/HDFS.
* [fix](file-writer) avoid empty file for segment writer (#31169)
---------
Co-authored-by: AlexYue <yj976240184@gmail.com>
Co-authored-by: zxealous <zhouchangyue@baidu.com>
If the original data is：
```sql
+-----------------------------------------------------+
| s_info |
+-----------------------------------------------------+
| {"s_id": 2, "s_name": "nereids", "s_address": "20"} |
| {"s_id": 1, "s_name": "doris", "s_address": "18"} |
+-----------------------------------------------------+
```
In the original logic, the struct type data exported to a csv file format did not contain column names,like
```
{2, "nereids", "20"}
{1, "doris", "18"}
```
This pr do not need to be merged into branch-2.0
This pr makes three changes to the display of complex types：
1. NULL value in complex types refers to being displayed as `null`, not `NULL`
2. struct type is displayed as "column_name": column_value
3. Time types such as `datetime` and `date`, are displayed with double quotes in complex types. like
`{1, "2023-10-26 12:12:12"}`
This pr also do a code refactor:
1. nesting_level is set to a member variable of the `DataTypeSerDe`, rather than a parameter in methods.
What's more, this pr fix a bug that fileSize is not correct, introduced by this pr: #25854
