Update docs

Signed-off-by: Tim Vaillancourt <[email protected]>

Author: timvaillancourt

doc/command-line-flags.md

@@ -106,6 +106,10 @@ Optional. Default is `safe`. See more discussion in [`cut-over`](cut-over.md)
 
 Default `3`.  Max number of seconds to hold locks on tables while attempting to cut-over (retry attempted when lock exceeds timeout).
 
+### cut-over-wait-timeout-seconds
+
+When set to a value greater than zero, this flag causes `gh-ost` to set a [MySQL `wait_timeout`](https://dev.mysql.com/doc/refman/8.0/en/server-system-variables.html#sysvar_wait_timeout) for the MySQL session performing the cut-over, specified in seconds. This timeout is to ensure the locks held by the cut-over are released if the `gh-ost` process terminates or pauses mid-cut-over.
+
 ### discard-foreign-keys
 
 **Danger**: this flag will _silently_ discard any foreign keys existing on your table.
@@ -202,10 +206,6 @@ List of metrics and threshold values; topping the threshold of any will cause th
 
 Typically `gh-ost` is used to migrate tables on a master. If you wish to only perform the migration in full on a replica, connect `gh-ost` to said replica and pass `--migrate-on-replica`. `gh-ost` will briefly connect to the master but otherwise will make no changes on the master. Migration will be fully executed on the replica, while making sure to maintain a small replication lag.
 
-### mysql-wait-timeout
-
-If set to a value greater than zero, causes `gh-ost` to set a provided [MySQL `wait_timeout`](https://dev.mysql.com/doc/refman/8.0/en/server-system-variables.html#sysvar_wait_timeout) for MySQL sessions opened by `gh-ost`, specified in seconds.
-
 ### postpone-cut-over-flag-file
 
 Indicate a file name, such that the final [cut-over](cut-over.md) step does not take place as long as the file exists.

go/logic/applier.go

@@ -977,21 +977,23 @@ func (this *Applier) AtomicCutOverMagicLock(sessionIdChan chan int64, tableLocke
 		return err
 	}
 
-	this.migrationContext.Log.Infof("Setting cut-over idle timeout as %d seconds", this.migrationContext.CutOverIdleTimeoutSeconds)
-	query = fmt.Sprintf(`set /* gh-ost */ session wait_timeout:=%d`, this.migrationContext.CutOverIdleTimeoutSeconds)
-	if _, err := tx.Exec(query); err != nil {
-		tableLocked <- err
-		return err
-	}
-	defer func() {
-		this.migrationContext.Log.Infof("Restoring applier idle timeout as %d seconds", this.migrationContext.ApplierWaitTimeout)
-		query = fmt.Sprintf(`set /* gh-ost */ session wait_timeout:=%d`, this.migrationContext.ApplierWaitTimeout)
-		if _, err := sqlutils.ExecNoPrepare(this.db, query); err != nil {
-			this.migrationContext.Log.Errorf("Failed to restore applier wait_timeout to %d seconds: %v",
-				this.migrationContext.ApplierWaitTimeout, err,
-			)
+	if this.migrationContext.CutOverIdleTimeoutSeconds > 0 {
+		this.migrationContext.Log.Infof("Setting cut-over idle timeout as %d seconds", this.migrationContext.CutOverIdleTimeoutSeconds)
+		query = fmt.Sprintf(`set /* gh-ost */ session wait_timeout:=%d`, this.migrationContext.CutOverIdleTimeoutSeconds)
+		if _, err := tx.Exec(query); err != nil {
+			tableLocked <- err
+			return err
 		}
-	}()
+		defer func() {
+			this.migrationContext.Log.Infof("Restoring applier idle timeout as %d seconds", this.migrationContext.ApplierWaitTimeout)
+			query = fmt.Sprintf(`set /* gh-ost */ session wait_timeout:=%d`, this.migrationContext.ApplierWaitTimeout)
+			if _, err := sqlutils.ExecNoPrepare(this.db, query); err != nil {
+				this.migrationContext.Log.Errorf("Failed to restore applier wait_timeout to %d seconds: %v",
+					this.migrationContext.ApplierWaitTimeout, err,
+				)
+			}
+		}()
+	}
 
 	if err := this.CreateAtomicCutOverSentryTable(); err != nil {
 		tableLocked <- err