executor: only forbid setting tidb_snapshot in stale txn (pingcap#25794)

CheneyDing · Jul 12, 2021 · c8bcc3b · c8bcc3b
1 parent d4a17a6
commit c8bcc3b
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Showing 2 changed files with 7 additions and 3 deletions.
diff --git a/executor/set.go b/executor/set.go
@@ -150,8 +150,10 @@ func (e *SetExecutor) setSysVariable(ctx context.Context, name string, v *expres
 	}
 	if sessionVars.InTxn() {
 		if name == variable.TxnIsolationOneShot ||
-			name == variable.TiDBTxnReadTS ||
-			name == variable.TiDBSnapshot {
+			name == variable.TiDBTxnReadTS {
+			return errors.Trace(ErrCantChangeTxCharacteristics)
+		}
+		if name == variable.TiDBSnapshot && sessionVars.TxnCtx.IsStaleness {
 			return errors.Trace(ErrCantChangeTxCharacteristics)
 		}
 	}

diff --git a/executor/stale_txn_test.go b/executor/stale_txn_test.go
@@ -378,9 +378,11 @@ func (s *testStaleTxnSuite) TestStalenessAndHistoryRead(c *C) {
 	c.Assert(tk.Se.GetInfoSchema().SchemaMetaVersion(), Equals, schemaVer2)
 
 	// test snapshot mutex with txn
-	tk.MustExec("START TRANSACTION")
+	tk.MustExec(fmt.Sprintf(`START TRANSACTION READ ONLY AS OF TIMESTAMP '%s'`, time2.Format("2006-1-2 15:04:05.000")))
 	c.Assert(tk.Se.GetSessionVars().SnapshotTS, Equals, uint64(0))
+	c.Assert(tk.Se.GetSessionVars().TxnCtx.StartTS, Equals, time2TS)
 	c.Assert(tk.Se.GetSessionVars().SnapshotInfoschema, IsNil)
+	c.Assert(tk.Se.GetInfoSchema().SchemaMetaVersion(), Equals, schemaVer2)
 	err := tk.ExecToErr(`set @@tidb_snapshot="2020-10-08 16:45:26";`)
 	c.Assert(err, ErrorMatches, ".*Transaction characteristics can't be changed while a transaction is in progress")
 	c.Assert(tk.Se.GetSessionVars().SnapshotTS, Equals, uint64(0))