*: add trace support for the AllocAutoIncrementValue function

[tiancaiamao]

What problem does this PR solve?

AllocAutoIncrementValue may need to visit the network and be slow, add trace support for it.

mysql> create table xx (a int, b int key auto_increment);
Query OK, 0 rows affected (0.03 sec)
mysql> trace insert into xx (a) values (666);

For example, from the following image, we can see that dominant cost in InsertExec.Next is AllocAutoIncrementValue.

And AllocAutoIncrementValue is much faster after the first time it's been executed, because alloc would cache a batch of ids:

mysql> trace format='row' insert into xx (a) values (66);
+----------------------------------------+-----------------+------------+
| operation                              | startTS         | duration   |
+----------------------------------------+-----------------+------------+
| session.getTxnFuture                   | 11:08:11.924668 | 4.009µs    |
|   ├─session.Execute                    | 11:08:11.924660 | 940.11µs   |
|   ├─session.ParseSQL                   | 11:08:11.924717 | 33.085µs   |
|   ├─executor.Compile                   | 11:08:11.924775 | 80.327µs   |
|   ├─session.runStmt                    | 11:08:11.924876 | 669.409µs  |
|   ├─executor.handleNoDelayExecutor     | 11:08:11.924904 | 170.199µs  |
|   ├─*executor.InsertExec.Next          | 11:08:11.924913 | 142.591µs  |
|   ├─table.AllocAutoIncrementValue      | 11:08:11.924971 | 6.702µs    |
|   └─session.CommitTxn                  | 11:08:11.925113 | 396.121µs  |
+----------------------------------------+-----------------+------------+
9 rows in set (0.01 sec)

What is changed and how it works?

Add those lines to AllocAutoIncrementValue:

	if span := opentracing.SpanFromContext(ctx); span != nil && span.Tracer() != nil {
		span1 := span.Tracer().StartSpan("table.AllocAutoIncrementValue", opentracing.ChildOf(span.Context()))
		defer span1.Finish()
	}

Tiny refactor for the ctx parameter in AllocAutoIncrementValue.

Check List

Tests

• Manual test (add detailed scripts or steps below)

Code changes

• Has exported function/method change

[tiancaiamao]

PTAL @lysu @jackysp

[jackysp]

Great!

[jackysp]

LGTM

[tiancaiamao]

/run-all-tests

[tiancaiamao]

/run-unit-test

[tiancaiamao]

PTAL @lysu

[lysu]

LGTM

[codecov]

Codecov Report

Merging #11158 into master will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff             @@
##             master     #11158   +/-   ##
===========================================
  Coverage   81.0651%   81.0651%           
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  Files           423        423           
  Lines         90051      90051           
===========================================
  Hits          73000      73000           
  Misses        11773      11773           
  Partials       5278       5278