replication: Support GTID tag in PreviousGTIDsEvent #952

dveeden · 2024-11-21T12:25:00Z

Issue: ref #845

The PreviousGTIDsEvent / PREVIOUS_GTIDS_LOG_EVENT has changed to work with tagged GTIDs.

First the uuidCount has changed, it encodes the GTID format. Here format 1 is tagged and format 0 is untagged.

Then each entry may have a tag. If there is a tag then the uuid itself isn't printed but the tag is appended to the last entry.

Example 1

896e7882-18fe-11ef-ab88-22222d34d411:1-3

regular format, compatible with both formats

Example 2

896e7882-18fe-11ef-ab88-22222d34d411:1-4:aaaa:1

tagged format.

Combination of

896e7882-18fe-11ef-ab88-22222d34d411:1-4
896e7882-18fe-11ef-ab88-22222d34d411:aaaa:1

Example 3

896e7882-18fe-11ef-ab88-22222d34d411:1-4:aaaa:1:abc:1-3:bbbbb:1:bbbbbb:1:x:1,896e7882-18fe-11ef-ab88-22222d34d412:1-2

Combination of:

896e7882-18fe-11ef-ab88-22222d34d411:1-4
                                    :aaaa:1
                                    :abc:1-3
                                    :bbbbb:1
                                    :bbbbbb:1
                                    :x:1,
896e7882-18fe-11ef-ab88-22222d34d412:1-2

Please also see: mysqlbinlog --read-from-remote-server --hexdump $binlogfile to see how MySQL encodes/decodes this.

See also:

https://dev.mysql.com/doc/refman/8.4/en/replication-gtids-concepts.html

Issue: ref go-mysql-org#845 The `PreviousGTIDsEvent` / `PREVIOUS_GTIDS_LOG_EVENT` has changed to work with tagged GTIDs. First the `uuidCount` has changed, it encodes the GTID format. Here format 1 is tagged and format 0 is untagged. Then each entry may have a tag. If there is a tag then the uuid itself isn't printed but the tag is appended to the last entry. Examples: `896e7882-18fe-11ef-ab88-22222d34d411:1-3` regular format, compatible with both formats `896e7882-18fe-11ef-ab88-22222d34d411:1-4:aaaa:1` tagged format. Combination of - `896e7882-18fe-11ef-ab88-22222d34d411:1-4` - `896e7882-18fe-11ef-ab88-22222d34d411:aaaa:1` `896e7882-18fe-11ef-ab88-22222d34d411:1-4:aaaa:1:abc:1-3:bbbbb:1:bbbbbb:1:x:1,896e7882-18fe-11ef-ab88-22222d34d412:1-2` Combination of: ``` 896e7882-18fe-11ef-ab88-22222d34d411:1-4 :aaaa:1 🔤1-3 :bbbbb:1 :bbbbbb:1 ❌1, 896e7882-18fe-11ef-ab88-22222d34d412:1-2 ``` Please also see: `mysqlbinlog --read-from-remote-server --hexdump $binlogfile` to see how MySQL encodes/decodes this. See also: - https://dev.mysql.com/doc/refman/8.4/en/replication-gtids-concepts.html

lance6716

I'm not sure Example 3 in PR description has the same format as MySQL. In https://dev.mysql.com/doc/refman/8.4/en/replication-gtids-concepts.html , there's

GTIDs originating from the same server but having different tags are treated in a manner similar to those originating from different servers, like this:

3E11FA47-71CA-11E1-9E33-C80AA9429562:Domain_1:1-3:15-21, 3E11FA47-71CA-11E1-9E33-C80AA9429562:Domain_2:8-52

rather than 3E11FA47-71CA-11E1-9E33-C80AA9429562:Domain_1:1-3:15-21:Domain_2:8-52. I guess the reason is if Domain_2 is replaced by tag 23, we will see 3E11FA47-71CA-11E1-9E33-C80AA9429562:Domain_1:1-3:15-21:23:8-52, which is ambiguous.

lance6716 · 2024-11-23T14:31:50Z

replication/event.go

+	GtidFormatTagged
+)
+
+func decodeSid(data []byte) (format GtidFormat, sidnr uint64) {


can you put the referenced MySQL source code or document in comment, so other reviewers can double check the implementation?

dveeden · 2024-11-26T19:23:48Z

I'm not sure Example 3 in PR description has the same format as MySQL. In https://dev.mysql.com/doc/refman/8.4/en/replication-gtids-concepts.html , there's

GTIDs originating from the same server but having different tags are treated in a manner similar to those originating from different servers, like this:

3E11FA47-71CA-11E1-9E33-C80AA9429562:Domain_1:1-3:15-21, 3E11FA47-71CA-11E1-9E33-C80AA9429562:Domain_2:8-52

rather than 3E11FA47-71CA-11E1-9E33-C80AA9429562:Domain_1:1-3:15-21:Domain_2:8-52. I guess the reason is if Domain_2 is replaced by tag 23, we will see 3E11FA47-71CA-11E1-9E33-C80AA9429562:Domain_1:1-3:15-21:23:8-52, which is ambiguous.

mysql-9.1.0> SET gtid_next='automatic:aaa';
Query OK, 0 rows affected (0.00 sec)

mysql-9.1.0> INSERT INTO t1 VALUES (1);
Query OK, 1 row affected (0.01 sec)

mysql-9.1.0> INSERT INTO t1 VALUES (2);
Query OK, 1 row affected (0.01 sec)

mysql-9.1.0> SET gtid_next='automatic:bbbb';
Query OK, 0 rows affected (0.00 sec)

mysql-9.1.0> INSERT INTO t1 VALUES (3);
Query OK, 1 row affected (0.01 sec)

mysql-9.1.0> INSERT INTO t1 VALUES (4);
Query OK, 1 row affected (0.01 sec)

mysql-9.1.0> INSERT INTO t1 VALUES (5);
Query OK, 1 row affected (0.01 sec)

mysql-9.1.0> INSERT INTO t1 VALUES (6);
Query OK, 1 row affected (0.01 sec)

mysql-9.1.0> SET gtid_next='automatic:c';
Query OK, 0 rows affected (0.00 sec)

mysql-9.1.0> INSERT INTO t1 VALUES (7);
Query OK, 1 row affected (0.01 sec)

mysql-9.1.0> SET gtid_next='automatic:d';
Query OK, 0 rows affected (0.00 sec)

mysql-9.1.0> INSERT INTO t1 VALUES (8);
Query OK, 1 row affected (0.01 sec)

mysql-9.1.0> SET gtid_next='automatic';
Query OK, 0 rows affected (0.00 sec)

mysql-9.1.0> INSERT INTO t1 VALUES (9);
Query OK, 1 row affected (0.01 sec)

mysql-9.1.0> SET gtid_next='automatic:123';
ERROR 1774 (HY000): Malformed GTID specification 'automatic:123'.
mysql-9.1.0> show global variables like 'gtid_executed';
+---------------+-----------------------------------------------------------------+
| Variable_name | Value                                                           |
+---------------+-----------------------------------------------------------------+
| gtid_executed | 30c380a5-ac28-11ef-b590-ba33c4017a43:1:aaa:1-2:bbbb:1-4:c:1:d:1 |
+---------------+-----------------------------------------------------------------+
1 row in set (0.02 sec)

mysql-9.1.0> SELECT VERSION();
+-----------+
| VERSION() |
+-----------+
| 9.1.0     |
+-----------+
1 row in set (0.00 sec)

It looks like my example might be correct and the MySQL docs might not be in sync with the actual behavior.

Note that 23 can't be a valid tag.

From https://dev.mysql.com/doc/dev/mysql-server/latest/classmysql_1_1gtid_1_1Tag.html

Representation of the GTID tag.

Tag format: [a-z_]{a-z0-9_}{0,31} Tag may be created from a given text. Text may contain leading and trailing 
spaces which will be omitted during Tag creation. Text may also contain uppercase characters. Acceptable 
format for text is as follows: [:space:][a-zA-Z_][a-zA-Z0-9_]{0,31}[:space:]

dveeden · 2024-11-26T20:38:23Z

And with the exact GTIDs from the docs:

mysql-9.1.0> reset binary logs and gtids;
Query OK, 0 rows affected (0.03 sec)

mysql-9.1.0> set global gtid_purged='3E11FA47-71CA-11E1-9E33-C80AA9429562:Domain_1:1-3:15-21, 
    '> 3E11FA47-71CA-11E1-9E33-C80AA9429562:Domain_2:8-52';
Query OK, 0 rows affected (0.02 sec)

mysql-9.1.0> show global variables like 'gtid%';
+----------------------------------+-----------------------------------------------------------------------+
| Variable_name                    | Value                                                                 |
+----------------------------------+-----------------------------------------------------------------------+
| gtid_executed                    | 3e11fa47-71ca-11e1-9e33-c80aa9429562:domain_1:1-3:15-21:domain_2:8-52 |
| gtid_executed_compression_period | 0                                                                     |
| gtid_mode                        | ON                                                                    |
| gtid_owned                       |                                                                       |
| gtid_purged                      | 3e11fa47-71ca-11e1-9e33-c80aa9429562:domain_1:1-3:15-21:domain_2:8-52 |
+----------------------------------+-----------------------------------------------------------------------+
5 rows in set (0.00 sec)

dveeden · 2024-11-26T20:44:43Z

I've filed https://bugs.mysql.com/bug.php?id=116789 for this

dveeden · 2024-11-27T07:49:13Z

I also filed https://bugs.mysql.com/bug.php?id=116747 some days ago

lance6716

Just a pure code-related review. I'll check GTID encoding and decoding soon

lance6716 · 2024-11-27T13:10:57Z

replication/event.go

-	uuidCount := binary.LittleEndian.Uint16(data[pos : pos+8])
+
+	gtidinfo := make([]byte, 8)
+	copy(gtidinfo, data[:8])


I see that the new copy is caused by decodeSid will modify data in-place. How about let decodeSid copy the needed data? So there's no risk that in future we need to change the code and caller forget to copy it.

replication/event.go

lance6716 · 2024-11-27T13:11:39Z

replication/event.go

+		if format == GtidFormatTagged {
+			tagLength := int(data[pos]) / 2
+			pos += 1
+			if tagLength > 0 {


can the tag have zero length? please add comments

lance6716 · 2024-11-27T13:16:17Z

replication/event.go

@@ -254,9 +298,14 @@ func (e *PreviousGTIDsEvent) Decode(data []byte) error {
 			}
 			intervals[i] = interval
 		}
-		previousGTIDSets[i] = fmt.Sprintf("%s:%s", uuid, strings.Join(intervals, ":"))
+		if isTag {
+			previousGTIDSets[currentSetnr-1] += fmt.Sprintf(":%s:%s", tag, strings.Join(intervals, ":"))


Because string is immutable, string += will create a new string object each time. If there are too many tags the performance will drop. Maybe store every "tag+intervals" and join them once at all

Co-authored-by: lance6716 <[email protected]>

dveeden requested review from atercattus and lance6716 November 21, 2024 12:25

Add test

03ef43c

dveeden mentioned this pull request Nov 21, 2024

MySQL 8.3 will introduce new GTID format #845

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Merge branch 'master' into gtid_tag

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Update replication/event.go

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replication: Support GTID tag in PreviousGTIDsEvent #952

replication: Support GTID tag in PreviousGTIDsEvent #952

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replication: Support GTID tag in PreviousGTIDsEvent #952

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replication: Support GTID tag in PreviousGTIDsEvent #952

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dveeden commented Nov 21, 2024

Example 1

Example 2

Example 3

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