Understanding LAST_CONFLICT_FREE_TRANSACTION and TRANSACTIONS_COMMITTED_ALL_MEMBERS

[Geert Vanderkelen]

I am trying to understand the values for LAST_CONFLICT_FREE_TRANSACTION and
TRANSACTIONS_COMMITTED_ALL_MEMBERS from the `performance_schema.replication_group_member_stats`.

Below is some output of a monitoring query I'm trying to build for our Group Replication instances.
I have edited the UUIDs, and columns named shorter. Showing is a view of the stats every 2-5 seconds.

Question: on the SECONDARY the LAST_CONFLICT_FREE_TRANSACTION (last_tx) is higher than primary.
Then it is getting settled, and finally primary shows last_tx same as secondaries.
When last_tx is all equal, TRANSACTIONS_COMMITTED_ALL_MEMBERS (tx_committed) is then getting
equal, first first on the secondaries, and then primaries. Why?

Update: Using MySQL 8.0.17

Cheers,
Geert


+------------+-----------+-------------+-------------------+---------+----------------------+
| id | role | tx_in_queue | tx_in_apply_queue | last_tx | tx_committed |
+------------+-----------+-------------+-------------------+---------+----------------------+
| 66df2415.. | SECONDARY | 0 | 0 | 278539 | 9bef21ef...:1-278526 |
| 94bd1912.. | SECONDARY | 0 | 0 | 278526 | 9bef21ef...:1-278526 |
| d1cbd881.. | PRIMARY | 0 | 0 | 278526 | 9bef21ef...:1-278526 |
+------------+-----------+-------------+-------------------+---------+----------------------+

+------------+-----------+-------------+-------------------+---------+----------------------+
| id | role | tx_in_queue | tx_in_apply_queue | last_tx | tx_committed |
+------------+-----------+-------------+-------------------+---------+----------------------+
| 66df2415.. | SECONDARY | 0 | 0 | 278631 | 9bef21ef...:1-278526 |
| 94bd1912.. | SECONDARY | 0 | 0 | 278526 | 9bef21ef...:1-278526 |
| d1cbd881.. | PRIMARY | 0 | 0 | 278526 | 9bef21ef...:1-278526 |
+------------+-----------+-------------+-------------------+---------+----------------------+

+------------+-----------+-------------+-------------------+---------+----------------------+
| id | role | tx_in_queue | tx_in_apply_queue | last_tx | tx_committed |
+------------+-----------+-------------+-------------------+---------+----------------------+
| 66df2415.. | SECONDARY | 0 | 0 | 278758 | 9bef21ef...:1-278650 |
| 94bd1912.. | SECONDARY | 0 | 1 | 278650 | 9bef21ef...:1-278526 |
| d1cbd881.. | PRIMARY | 0 | 0 | 278670 | 9bef21ef...:1-278526 |
+------------+-----------+-------------+-------------------+---------+----------------------+

+------------+-----------+-------------+-------------------+---------+----------------------+
| id | role | tx_in_queue | tx_in_apply_queue | last_tx | tx_committed |
+------------+-----------+-------------+-------------------+---------+----------------------+
| 66df2415.. | SECONDARY | 0 | 0 | 278898 | 9bef21ef...:1-278650 |
| 94bd1912.. | SECONDARY | 0 | 0 | 278849 | 9bef21ef...:1-278650 |
| d1cbd881.. | PRIMARY | 0 | 0 | 278880 | 9bef21ef...:1-278650 |
+------------+-----------+-------------+-------------------+---------+----------------------+

+------------+-----------+-------------+-------------------+---------+----------------------+
| id | role | tx_in_queue | tx_in_apply_queue | last_tx | tx_committed |
+------------+-----------+-------------+-------------------+---------+----------------------+
| 66df2415.. | SECONDARY | 0 | 0 | 278898 | 9bef21ef...:1-278650 |
| 94bd1912.. | SECONDARY | 0 | 0 | 278898 | 9bef21ef...:1-278650 |
| d1cbd881.. | PRIMARY | 0 | 0 | 278898 | 9bef21ef...:1-278650 |
+------------+-----------+-------------+-------------------+---------+----------------------+

+------------+-----------+-------------+-------------------+---------+----------------------+
| id | role | tx_in_queue | tx_in_apply_queue | last_tx | tx_committed |
+------------+-----------+-------------+-------------------+---------+----------------------+
| 66df2415.. | SECONDARY | 0 | 0 | 278898 | 9bef21ef...:1-278898 |
| 94bd1912.. | SECONDARY | 0 | 0 | 278898 | 9bef21ef...:1-278650 |
| d1cbd881.. | PRIMARY | 0 | 0 | 278898 | 9bef21ef...:1-278650 |
+------------+-----------+-------------+-------------------+---------+----------------------+

+------------+-----------+-------------+-------------------+---------+----------------------+
| id | role | tx_in_queue | tx_in_apply_queue | last_tx | tx_committed |
+------------+-----------+-------------+-------------------+---------+----------------------+
| 66df2415.. | SECONDARY | 0 | 0 | 278898 | 9bef21ef...:1-278898 |
| 94bd1912.. | SECONDARY | 0 | 0 | 278898 | 9bef21ef...:1-278898 |
| d1cbd881.. | PRIMARY | 0 | 0 | 278898 | 9bef21ef...:1-278650 |
+------------+-----------+-------------+-------------------+---------+----------------------+

+------------+-----------+-------------+-------------------+---------+----------------------+
| id | role | tx_in_queue | tx_in_apply_queue | last_tx | tx_committed |
+------------+-----------+-------------+-------------------+---------+----------------------+
| 66df2415.. | SECONDARY | 0 | 0 | 278898 | 9bef21ef...:1-278898 |
| 94bd1912.. | SECONDARY | 0 | 0 | 278898 | 9bef21ef...:1-278898 |
| d1cbd881.. | PRIMARY | 0 | 0 | 278898 | 9bef21ef...:1-278898 |
+------------+-----------+-------------+-------------------+---------+----------------------+



Edited 1 time(s). Last edit at 10/02/2019 02:02AM by Geert Vanderkelen.