ddl: ddl-owner try to use memory infoSchema to check first

[crazycs520]

What problem does this PR solve?

Make ddl-owner try to use memory infoschema to check first if the owner tidb-server already has loaded the latest schema.

Here is a simple test, There are 11394 tables in test20.
Deploy 1 tidb, 1 pd, 1 tikv.

create table

mysql root@localhost:test20> show tables;
11394 rows in set
Time: 0.253s

Before, spend 0.37s, checkTableNotExists spend 0.34s

mysql root@localhost:test20> create table tb (a int);
Query OK, 0 rows affected
Time: 0.371s 

In this PR: spend 0.07s, checkTableNotExists spend 267us.

mysql root@localhost:test20> create table ta (a int);
Query OK, 0 rows affected
Time: 0.070s

Create database

There are 18500 databases already in TiDB.

mysql root@localhost:test> show databases;
18500 rows in set
Time: 0.546s

Before: spend 0.32S, and checkSchemaExist spend 250ms.

mysql root@localhost:test> create database dbd4
Query OK, 0 rows affected
Time: 0.326s

In this PR: 0.08s, checkSchemaExist spend 1 ms.

mysql root@localhost:test> create database dbd2
Query OK, 0 rows affected
Time: 0.080s

What is changed and how it works?

Change checkTableNotExists function.

Check List

Tests

• No test...

Code changes

• Has exported function/method change

Related changes

• Need to cherry-pick to the release branch ?

[codecov]

Codecov Report

Merging #10170 into master will increase coverage by 0.0167%.
The diff coverage is 77.4647%.

@@               Coverage Diff                @@
##             master     #10170        +/-   ##
================================================
+ Coverage   77.9363%   77.9531%   +0.0167%     
================================================
  Files           407        407                
  Lines         83463      83531        +68     
================================================
+ Hits          65048      65115        +67     
+ Misses        13588      13584         -4     
- Partials       4827       4832         +5

[crazycs520]

/run-all-tests

[winkyao]

LGTM

[bb7133]

LGTM

[tiancaiamao]

LGTM