executor: fix issue of explain for connection can't show the last query plan (#21242)

[ti-srebot]

cherry-pick #21242 to release-4.0

---

What problem does this PR solve?

close #21235

This bug is imported by #19296.

As the title said, here is an example:

test> select connection_id();
+---------------------+
| connection_id()     |
+---------------------+
| 5235610488678645763 |
+---------------------+
1 row in set
Time: 0.011s
test> select * from t where a=1;
+---+---+
| a | b |
+---+---+
| 1 | 1 |
+---+---+
1 row in set
Time: 0.012s
test> explain for connection 5235610488678645763;
+-------------+---------+---------+------+---------------+----------------------------------------------------------------+---------------+--------+------+
| id          | estRows | actRows | task | access object | execution info                                                 | operator info | memory | disk |
+-------------+---------+---------+------+---------------+----------------------------------------------------------------+---------------+--------+------+
| Point_Get_1 | 1.00    | 1       | root | table:t       | time:884.141µs, loops:2, Get:{num_rpc:1, total_time:510.211µs} | handle:1      | N/A    | N/A  |
+-------------+---------+---------+------+---------------+----------------------------------------------------------------+---------------+--------+------+

What is changed and how it works?

1. Keep saving last valid plan when the connection is sleeping.

Related changes

• Need to cherry-pick to the release branch

Check List

Tests

• Unit test

Side effects

• Performance regression
  • Consumes more CPU
  • Consumes more MEM

Release note

• fix issue of explain for connection can't show the last query plan/

[ti-srebot]

/run-all-tests

[ti-srebot]

@crazycs520 you're already a collaborator in bot's repo.

[crazycs520]

/merge

[ti-srebot]

@crazycs520 Oops! This PR requires at least 1 LGTMs to merge. The current number of LGTM is 0

[SunRunAway]

LGTM

[crazycs520]

/merge

[ti-srebot]

Your auto merge job has been accepted, waiting for:

• 21287
• 21003
• 21171
• 20919
• 21211
• 21298

[ti-srebot]

/run-all-tests

[ti-srebot]

@ti-srebot merge failed.

[AilinKid]

LGTM

[crazycs520]

/merge

[ti-srebot]

/run-all-tests