statistics: remove unreachable code

[hi-rustin]

What is changed and how it works?

Removed some unreachable code. The code is now unreachable as TiDB no longer sends mixed analyze requests to TiKV if the statistics version is set to 2.

You can only find one reference of the mixed request type in TiDB.

You can find it here: https://github.com/pingcap/tidb/blob/12b37d88dceb4eb4da6fe316fb4d0af2024ab58b/pkg/executor/builder.go#L2706

But for version 2, we use buildAnalyzeSamplingPushdown to build the analysis task.

Issue Number: Ref #16463

What's Changed:

statistics: remove unreachable code

The code is now unreachable as TiDB no longer
sends mixed analyze requests to TiKV if the
statistics version is set to 2.

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• Need to cherry-pick to the release branch

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Release note

None

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This pull request has been approved by:

• Connor1996
• JmPotato

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[hi-rustin]

🔢 Self-check (PR reviewed by myself and ready for feedback.)

[Connor1996]

LGTM

[hi-rustin]

🔢 Self-check (PR reviewed by myself and ready for feedback.)

[hi-rustin]

🔢 Self-check (PR reviewed by myself and ready for feedback.)

[hi-rustin]

Test locally:

1. Start the tidb cluster with patch: tiup playground nightly --kv.binpath /Volumes/t7/code/tikv/target/aarch64-apple-darwin/debug/tikv-server

mysql>  select * from information_schema.cluster_info;
+---------+-----------------+-----------------+---------------------------+------------------------------------------+---------------------+--------------+-----------+
| TYPE    | INSTANCE        | STATUS_ADDRESS  | VERSION                   | GIT_HASH                                 | START_TIME          | UPTIME       | SERVER_ID |
+---------+-----------------+-----------------+---------------------------+------------------------------------------+---------------------+--------------+-----------+
| tidb    | 127.0.0.1:4000  | 127.0.0.1:10080 | 8.2.0-alpha-3-g79c1499bec | 79c1499bec7e609a051634c87460511b203c5389 | 2024-05-11 15:01:48 | 9m0.4416s    |       713 |
| pd      | 127.0.0.1:2379  | 127.0.0.1:2379  | 8.2.0-alpha-1-g4a7bffcb3  | 4a7bffcb3baf7a8e2515e70834d8567bc17439da | 2024-05-11 15:01:18 | 9m30.441602s |         0 |
| tiflash | 127.0.0.1:3930  | 127.0.0.1:20292 | 8.2.0-alpha-17-g8e50de84e | 8e50de84e6d6ecdcc108990217b70b6bb3f50271 | 2024-05-11 15:01:55 | 8m53.441603s |         0 |
| tikv    | 127.0.0.1:20160 | 127.0.0.1:20180 | 8.2.0-alpha               | 87c9a2a0965ae512fd254e26733ccc0c424bb36a | 2024-05-11 15:01:27 | 9m21.441603s |         0 |
+---------+-----------------+-----------------+---------------------------+------------------------------------------+---------------------+--------------+-----------+
4 rows in set (0.01 sec)

2. Create a table and analyze with stats version 2:

create table t(a int);

import { Client } from "https://deno.land/x/mysql/mod.ts";

const client = await new Client().connect({
  hostname: "127.0.0.1",
  port: 4000,
  username: "root",
  db: "test",
  password: "",
});

for (let i = 0; i < 2000; i++) {
  await client.execute(`INSERT INTO t (a) VALUES (?)`, [i]);
  if (i % 2 === 0) {
    await client.execute(`INSERT INTO t (a) VALUES (?)`, [i]);
  }
}

await client.close();;

analyze table t;

4. Create another table and analyze it with statistics version 1:

create table t1(a int);

import { Client } from "https://deno.land/x/mysql/mod.ts";

const client = await new Client().connect({
  hostname: "127.0.0.1",
  port: 4000,
  username: "root",
  db: "test",
  password: "",
});

for (let i = 0; i < 2000; i++) {
  await client.execute(`INSERT INTO t1 (a) VALUES (?)`, [i]);
  if (i % 2 === 0) {
    await client.execute(`INSERT INTO t1 (a) VALUES (?)`, [i]);
  }
}

await client.close();;

set @@session.tidb_analyze_version=1;
analyze table t1;

6. Create a new table with a string index:

create table t2(a varchar(50), b int, PRIMARY KEY (a));

import { Client } from "https://deno.land/x/mysql/mod.ts";

const client = await new Client().connect({
  hostname: "127.0.0.1",
  port: 4000,
  username: "root",
  db: "test",
  password: "",
});

for (let i = 0; i < 2000; i++) {
  const a = `string${i}`;
  const b = i;
  await client.execute(`INSERT INTO t2 (a, b) VALUES (?, ?)`, [a, b]);
}

await client.close();

set @@session.tidb_analyze_version=1;
analyze table t2;

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[hi-rustin]

For the backward compatibility:

1. This code has been unreachable since v5.1.0.
2. For tidb v5.0.x, we didn't allow users to use the analysis version 2.

[overvenus]

/merge

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This pull request has been accepted and is ready to merge.

Commit hash: cca919d