LOAD DATA behavior change causes upgrade issue #19809
Description
Bug Report
Please answer these questions before submitting your issue. Thanks!
1. Minimal reproduce step (Required)
See my comment here and pingcap/docs#3838
There is an issue in that to restore the previous behavior for LOAD DATA, because tidb_dml_batch_size is only session scope. Therefore, you must SET tidb_dml_batch_size=20000 for each session, but there are some common cases where that is hard to do:
- It is a closed source app (and they can't modify the code)
- The client library handles session scope in a weird way (by default Golang uses a connection pool, and will only provide session scope guarantees with a connection pool).
Because this is a breaking change, I propose allowing GLOBAL | SESSION scope. This will allow an upgrade path, because the TiDB server can be set to the previous behavior.
2. What did you expect to see? (Required)
A small change: tidb_dml_batch_size is SESSION | GLOBAL scope. I prefer the new behavior, I am just concerned about upgrades.
3. What did you see instead (Required)
SESSION scope only
4. What is your TiDB version? (Required)
mysql> select tidb_version()\G
*************************** 1. row ***************************
tidb_version(): Release Version: v4.0.0-beta.2-1142-gebb557386
Edition: Community
Git Commit Hash: ebb55738695d01048f747a43592331e3e2443988
Git Branch: master
UTC Build Time: 2020-09-03 15:56:39
GoVersion: go1.13
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false
1 row in set (0.00 sec)