Bug #108537 gtid_subset should reset null_value to false
Submitted: 19 Sep 13:29 Modified: 19 Sep 13:58
Reporter: casa zhang (OCA) Email Updates:
Status: Verified Impact on me:
None 
Category:MySQL Server: Replication Severity:S2 (Serious)
Version:5.7 OS:Any
Assigned to: CPU Architecture:Any

[19 Sep 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 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 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.