ttl deletion is not recorded in the stats

[YangKeao]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

CREATE TABLE t1(id int, id_2 int, t timestamp, PRIMARY KEY (id, id_2)) TTL=`t` + INTERVAL 1 DAY

Insert 10000 rows，6667 of them expired. After a period of time，run SHOW STATS_META to check whether the stats is updated.

2. What did you expect to see? (Required)

Auto analyze should be triggered

3. What did you see instead (Required)

It's not updated, Modify_count is also not updated.

MySQL [test]> SHOW STATS_META;
+---------+------------+----------------+---------------------+--------------+-----------+
| Db_name | Table_name | Partition_name | Update_time         | Modify_count | Row_count |
+---------+------------+----------------+---------------------+--------------+-----------+
| test    | t1         |                | 2022-12-22 16:03:34 |            0 |     10000 |
+---------+------------+----------------+---------------------+--------------+-----------+
1 row in set (0.001 sec)

4. What is your TiDB version? (Required)

Release Version: v6.6.0-alpha
Edition: Community
Git Commit Hash: fc3f04b
Git Branch: heads/refs/tags/v6.6.0-alpha
UTC Build Time: 2022-12-21 14:38:34
GoVersion: go1.19.3
Race Enabled: false
TiKV Min Version: 6.2.0-alpha
Check Table Before Drop: false
Store: tikv

[YangKeao]

The sys session is not equipped with a stats collector. But the stats collector is a private field, I'm not sure whether I should set it after getting and delete it before returning it to the pool, or setup a new session pool with stats collector 🤔