Bug #108537 gtid_subset should reset null_value to false

• Submitted: 19 Sep 2022 13:29
• Modified: 19 Sep 2022 13:58
• Reporter: casa zhang (OCA)
• Status: Verified
• Category: MySQL Server: Replication
• Severity: S2 (Serious)
• Version: 5.7
• OS: Any
• CPU Architecture: Any

[19 Sep 2022 13:29] casa zhang

Description:
From Tencent CDB group, casazhang

hi, something go wrong with an application online, finally we found that gtid_subset should reset null_value to false, otherwise records will be lost when scanning multiple records.

How to repeat:
create table t1 ( c1 int, c2 text);

insert into t1 values (1, '{\"time\":\"2022-09-18 17:18:12\"}');
insert into t1 values (2, '{\"time\":\"2022-09-19 17:18:12\", \"gtid_set_column\":\"c55be2ea-14fc-12ec-a970-043f72e646cf:1-6667608119\"}');
insert into t1 values (3, '{\"time\":\"2022-09-20 17:18:12\"}');
insert into t1 values (4, '{\"time\":\"2022-09-21 17:18:12\", \"gtid_set_column\":\"c55be2ea-14fc-12ec-a970-043f72e646cf:1-6667608114\"}');
insert into t1 values (5, '{\"time\":\"2022-09-22 17:18:12\"}');
insert into t1 values (6, '{\"time\":\"2022-09-23 17:18:12\", \"gtid_set_column\":\"03465097-563b-12ec-a4cb-0c42a14d69f3:1-234648230\"}');
insert into t1 values (7, '{\"time\":\"2022-09-24 17:18:12\"}');

select t1.c1 from t1 where gtid_subset(trim('"' from json_extract(t1.c2, '$.gtid_set_column')), "03465097-563b-12ec-a4cb-0c42a14d69f3:1-234648290") = 0;

drop table t1;

the result should be as follows:

mysql> select t1.c1 from t1 where gtid_subset(trim('"' from json_extract(t1.c2, '$.gtid_set_column')), "03465097-563b-12ec-a4cb-0c42a14d69f3:1-234648290") = 0;
+------+
| c1   |
+------+
|    2 |
|    4 |
+------+
2 rows in set (0.00 sec)

but, it return 0 rows.

Suggested fix:
longlong Item_func_gtid_subset::val_int()
 {
   DBUG_ENTER("Item_func_gtid_subset::val_int()");
-  if (args[0]->null_value || args[1]->null_value)
-  {
-    null_value= true;
-    DBUG_RETURN(0);
-  }
   String *string1, *string2;
   const char *charp1, *charp2;
   int ret= 1;
   enum_return_status status;
-  // get strings without lock
-  if ((string1= args[0]->val_str(&buf1)) != NULL &&
-      (charp1= string1->c_ptr_safe()) != NULL &&
-      (string2= args[1]->val_str(&buf2)) != NULL &&
-      (charp2= string2->c_ptr_safe()) != NULL)
+  null_value= false;
+  if ((string1 = args[0]->val_str(&buf1)) == NULL ||
+      (string2 = args[1]->val_str(&buf2)) == NULL)
   {
+    null_value = true;
+    ret = 0;
+  } else if ((charp1= string1->c_ptr_safe()) != NULL &&
+      (charp2= string2->c_ptr_safe()) != NULL)
+  { // get strings without lock

[19 Sep 2022 13:30] casa zhang

gtid_subset should reset null_value to false

Attachment: 0001-bugfix-gtid_subset-should-reset-null_value-to-false.patch (application/octet-stream, text), 4.66 KiB.

[19 Sep 2022 13:58] MySQL Verification Team

Hi Mr. zhang,

Thank you for your bug report.

We have managed to repeat it.

Also, many, many thanks for the patch that you provided.

This bug is now verified as reported.