1. Spark can set the timestamp precision by the following configuration:
spark.sql.parquet.outputTimestampType = INT96(NANOS), TIMESTAMP_MICROS, TIMESTAMP_MILLIS
DATETIME V1 only keeps the second precision, DATETIME V2 keeps the microsecond precision.
2. If using DECIMAL V2, the BE saves the value as decimal128, and keeps the precision of decimal as (precision=27, scale=9). DECIMAL V3 can maintain the right precision of decimal
Increase compatibility with mysql
1. Added two system tables files and partitions
2. Improved the return logic of mysql error code to make the error code more compatible with mysql
3. Added lock/unlock tables statement and show columns statement for compatibility with mysql dump
4. Compatible with mysqldump tool, now you can use mysql dump to dump data and table structure from doris
now use mysqldump may print error message like
```
$ mysqldump -h127.0.0.1 -P9130 -uroot test_query_qa > a
mysqldump: Error: 'errCode = 2, detailMessage = select list expression not produced by aggregation output (missing from GROUP BY clause?): `EXTRA`' when trying to dump tablespaces
```
This error message not effect the export file, you can add `--no-tablespaces` to avoid this error
1. replace all boost::shared_ptr to std::shared_ptr
2. replace all boost::scopted_ptr to std::unique_ptr
3. replace all boost::scoped_array to std::unique<T[]>
4. replace all boost:thread to std::thread
1. Add metadata table 'statistics' to store index information;
2. In the header information returned by mysql, the data type length is returned according to the actual type.
