MySQL Bugs: #103305: Significantly reduced performance in the NativeDriver class

Bug #103305	Significantly reduced performance in the NativeDriver class
Submitted:	13 Apr 2021 13:10	Modified:	19 Apr 2021 11:38
Reporter:	Slava Tretyak	Email Updates:
Status:	Duplicate	Impact on me:	None
Category:	Connector / NET	Severity:	S1 (Critical)
Version:	8.0.23	OS:	Any
Assigned to:		CPU Architecture:	Any

Description:
The app is very very slow when loads a lot of records from the database.
it does not matter if it is getting a dataset or a data reader.
the more records query returns the slower the application.

I have found that NativeDriver class was added with a Regexp check in function 
public IMySqlValue ReadColumnValue(int index, MySqlField field, IMySqlValue valObject) (mysql-connector-net\MySQL.Data\src\NativeDriver.cs)

the function is called every time you read the data from each column and each row.

and each time it creates Regexp class like

Regex regex = new Regex(@"(?i)^[0-9A-F]{8}[-](?:[0-9A-F]{4}[-]){3}[0-9A-F]{12}$"); // check for GUID format

and it is very very expensive operation.

So when you load for instance 1M records with 5 columns from the database
it takes (in our case) about 10-15 minutes.

Also the entire CPU usage of the application became much higher.

How to repeat:
To repeat the issue just request 1M records from a table.
you can use either dataset or data reader

Suggested fix:
Regexp class is thread safe
so it can be moved to a static variable and be created one time

like

    private static Regex _guidRegexp = new Regex(@"(?i)^[0-9A-F]{8}[-](?:[0-9A-F]{4}[-]){3}[0-9A-F]{12}$"); // check for GUID format

and to use that one instance in 

public IMySqlValue ReadColumnValue

I have fixed the same in our fork and the same query with the same data is loaded 6 times faster.

I think it is critical issue because all the requests are affected.

Duplicate of bug #101714.

Hello Slava Tretyak,

Thank you for the report and feedback.
Imho this is duplicate of Bug #101714, please see Bug #101714.

Regards,
Ashwini Patil

Yes, it is the duplicate.
Sorry, I did not find somehow the same before reporting the issue.
Thanks.