Bug #97001 Dangerous optimization reconsidering_access_paths_for_index_ordering
Submitted: 25 Sep 2019 0:35 Modified: 26 Sep 2019 20:47
Reporter: Jeremy Cole (Basic Quality Contributor) (OCA) Email Updates:
Status: Verified Impact on me:
None 
Category:MySQL Server: Optimizer Severity:S2 (Serious)
Version:5.7, 5.7.27 OS:Any
Assigned to: CPU Architecture:Any
Tags: Contribution, limit, Optimizer, primary key, reconsidering_access_paths_for_index_ordering

File: Maximum allowed size is 3MB.
Description:
Privacy:

If the data you need to attach is more than 3MB, you should create a compressed archive of the data and a README file that describes the data with a filename that includes the bug number (recommended filename: mysql-bug-data-97001.zip) and upload one to sftp.oracle.com. A free Oracle Web (SSO) account (the one you use to login bugs.mysql.com) and a client that supports SFTP are required in order to access the SFTP server.

To upload the file to sftp.oracle.com:

  1. Open an SFTP client and connect to sftp.oracle.com. Specify port 2021 and remote directory /support/incoming/.
  2. Log in with your newly created Oracle Web account (email address) and password.
  3. Upload the archive to /support/incoming.
  4. Once you have uploaded the file, add a comment to this bug to notify us about it.
Example: sftp -oPort=2021 -oUser=email sftp.oracle.com:/support/incoming

Usage Notes: This directory is unlistable, which means that once you have uploaded your file, you will not be able to see it. A file cannot be uploaded more than once with the same filename. The filename must be changed before attempting to upload the file again. The filename should always start with mysql-bug- prefix. Files are retained on the SFTP server for 7 days and then permanently removed.

[25 Sep 2019 0:39] Jeremy Cole
Patch to implement reconsider_index_for_order optimizer_switch

Attachment: reconsider_index_for_order_20190924.patch.txt (text/plain), 8.20 KiB.

[25 Sep 2019 0:39] Jeremy Cole
Test case demonstrating slow query resulting from bad optimization

Attachment: reconsider_index_for_order_bad_optimization.test (application/octet-stream, text), 2.94 KiB.

[25 Sep 2019 7:10] Umesh Shastry
mtr test results -  5.7.27, 5.6.45 and 8.0.17

Attachment: 97001.results (application/octet-stream, text), 12.66 KiB.