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Signed-off-by: guo-shaoge <[email protected]>
pingcap · Dec 24, 2021 · 3ab1d4c · 3ab1d4c
1 parent ccbd8f2
commit 3ab1d4c
Showing 1 changed file with 2 additions and 0 deletions.
diff --git a/session/bootstrap.go b/session/bootstrap.go
@@ -1659,6 +1659,8 @@ func upgradeToVer80(s Session, ver int64) {
 		mysql.SystemDB, mysql.GlobalVariablesTable, variable.TiDBAnalyzeVersion, 1)
 }
 
+// For users that upgrade TiDB from a pre-4.0 version, we want to disable index merge by default.
+// This helps minimize query plan regressions.
 func upgradeToVer81(s Session, ver int64) {
 	if ver >= version81 {
 		return