MySQL Bugs: #101389: getwarnings should check warning count before sending SHOW

Bug #101389	getwarnings should check warning count before sending SHOW
Submitted:	30 Oct 2020 0:30	Modified:	11 Dec 2021 18:23
Reporter:	Trey Raymond	Email Updates:
Status:	Closed	Impact on me:	None
Category:	Connector / J	Severity:	S3 (Non-critical)
Version:	8.0, 5.1	OS:	Any
Assigned to:		CPU Architecture:	Any

Description:
refs
https://github.com/mysql/mysql-connector-j/blob/release/8.0/src/main/user-impl/java/com/my...

https://github.com/mysql/mysql-connector-j/blob/release/8.0/src/main/protocol-impl/java/co...

https://github.com/mysql/mysql-connector-j/blob/release/8.0/src/main/protocol-impl/java/co...

specifically this line
https://github.com/mysql/mysql-connector-j/blob/release/8.0/src/main/protocol-impl/java/co...

this function will send a 'show warnings' statement to the server even if the statement returned warningcount=0, which is quite expensive.  it should only send the SHOW query if count>0, else it already knows there are zero results.

How to repeat:
call getwarnings after any zero-warning statement, it will still run SHOW.
or use one of the popular libs like hibernate, jooq, etc which all suffer terribly from this.

Suggested fix:
wrap an if around that SHOW call.  easy fix!

Hello Trey Raymond,

Thank you for the report and feedback.

regards,
Umesh

Posted by developer:
 
Added the following entry to the Connector/J 8.0.28 changelog: 

"getWarnings() always sent a SHOW WARNINGS query to the server. With this fix, the query is sent only if there really are warnings to be shown, in order to save resources."

Bug#77394 is marked as a duplicate of this one.