executor: subtract the old txn size when track the mem usage (#18000)

[ti-srebot]

cherry-pick #18000 to release-4.0

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What problem does this PR solve?

Issue Number: close #17961

Problem Summary:

What is changed and how it works?

What's Changed:
subtract the old txn size when track the memusage of InsertExec.exec and ReplaceExec.exec

How it Works:

Related changes

• Need to cherry-pick to the release branch

Check List

Tests

• Manual test (add detailed scripts or steps below)

drop table if exists t2;
create table t2(a int);
insert into t2 values(1), (2), (3);
insert into t2 select * from t2;
insert into t2 select * from t2;
insert into t2 select * from t2;
insert into t2 select * from t2;
insert into t2 select * from t2;
insert into t2 select * from t2;
insert into t2 select * from t2;
insert into t2 select * from t2;
insert into t2 select * from t2;
insert into t2 select * from t2;
insert into t2 select * from t2;
insert into t2 select * from t2;
insert into t2 select * from t2;
insert into t2 select * from t2;
insert into t2 select * from t2;
insert into t2 select * from t2;
insert into t2 select * from t2;
insert into t2 select * from t2;

set tidb_mem_quota_query=1048576;
select * from t, t2 where t.a=t2.a;

insert into t2 select * from t2;

[2020/06/15 16:08:53.597 +08:00] [INFO] [set.go:207] ["set session var"] [conn=1] [name=tidb_mem_quota_query] [val=3145728]

[2020/06/15 16:08:56.029 +08:00] [WARN] [expensivequery.go:168] [expensive_query] [cost_time=0.404118444s] [stats=t2:417387901159735296] [conn_id=1] [user=root] [database=test] [table_ids="[45]"] [txn_start_ts=417387914362880000] [mem_max="3293321 Bytes (3.1407556533813477 MB)"] [sql="select * from t2"]

[2020/06/15 16:09:06.386 +08:00] [WARN] [expensivequery.go:168] [expensive_query] [cost_time=0.406845733s] [stats=t2:417387901159735296] [conn_id=1] [user=root] [database=test] [table_ids="[45]"] [txn_start_ts=417387917077118976] [mem_max="3293321 Bytes (3.1407556533813477 MB)"] [sql="insert into t2 select * from t2"]

Side effects

N/A

Release note

• Refine the memory usage counting of InsertExec and ReplaceExec.

[ti-srebot]

/run-all-tests

[ti-srebot]

@XuHuaiyu please accept the invitation then you can push to the cherry-pick pull requests.
https://github.com/ti-srebot/tidb/invitations

[jackysp]

LGTM

[lysu]

LGTM

[lysu]

/run-unit-test