@@global.default_week_format was not immediately loaded on new session, causing week() to use the wrong mode

[kennytm]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

First, change the global default_week_format

mysql -u root -h 127.0.0.1 -P 4000 -e "set global default_week_format = 4"

Then execute week() in a new connection.

mysql -u root -h 127.0.0.1 -P 4000 -E -e "select week('2020-02-02'), @@default_week_format, week('2020-02-02')"

2. What did you expect to see? (Required)

*************************** 1. row ***************************
   week('2020-02-02'): 6
@@default_week_format: 4
   week('2020-02-02'): 6

3. What did you see instead (Required)

*************************** 1. row ***************************
   week('2020-02-02'): 5
@@default_week_format: 4
   week('2020-02-02'): 6

The first execution of week('2020-02-02') used mode 0 instead of 4.

4. What is your TiDB version? (Required)

Repro with both v4.0.8 and nightly 62fd2b7

Release Version: v4.0.8
Edition: Community
Git Commit Hash: 66ac9fc31f1733e5eb8d11891ec1b38f9c422817
Git Branch: heads/refs/tags/v4.0.8
UTC Build Time: 2020-10-30 08:21:16
GoVersion: go1.13
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false

Release Version: v4.0.0-beta.2-1734-g62fd2b735
Edition: Community
Git Commit Hash: 62fd2b735934e67580fefade0584e9eeb63f32d3
Git Branch: master
UTC Build Time: 2020-12-04 12:32:58
GoVersion: go1.13
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false

[kennytm]

/label component/session,sig/DDL

[ti-srebot]

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