Bug #121177 different innodb_ddl_buffer_size for master and slave masy cause duplicated key error
Submitted: 27 Aug 7:59
Reporter: zhang xiaojian (OCA) Email Updates:
Status: Open Impact on me:
None 
Category:MySQL Server: InnoDB storage engine Severity:S2 (Serious)
Version:8.0.45, 8.4.8, 9.6.0 OS:Any
Assigned to: CPU Architecture:Any
Tags: replication 1062

[27 Aug 7:59] zhang xiaojian 
Description:
Bug #17657223 optimize the sort for inplace DDL, when add an auto increament key wich not need to resort data, may use skip_pk_sort path. The innodb_ddl_buffer_size use to store the new column value and write to new table when buffer is full.

I find when buffer cleared, one auto increate value is wasted. for example:

original table:
A
B
C
D
E
F

alter add new auto increate key and buffer is full after write (3, B)
1. A
2. B
3. C
5. D
6. E
7. F

That not a problem if we have only one primary instance.

If we have a primary-replica, and they have different innodb_ddl_buffer_size value.

The slave may have value after alter table statement applied:
1. A
2. B
4. C
5. D
7. E
8. F

The key of 8 has beed used in replica, if one more insert execute in primary, duplicated key error would break the replication.

How to repeat:
1. init a primary and slave with binlog replication.
2. primary: --innodb_ddl_buffer_size=1048576 slave:--innodb_ddl_buffer_size=65536
3. execute sql in primary 

```
CREATE DATABASE IF NOT EXISTS repro_skip_pk_sort_autoinc;
USE repro_skip_pk_sort_autoinc;

DROP TABLE IF EXISTS t_repro;
DROP TABLE IF EXISTS digits;

-- 缩小 DDL buffer，使 overflow 更容易、结果更明显。
-- SET SESSION innodb_ddl_buffer_size = 165536;
SET SESSION innodb_ddl_threads = 1;

-- 排除非默认自增步长的影响。
SET SESSION auto_increment_increment = 1;
SET SESSION auto_increment_offset = 1;

CREATE TABLE digits (
    n TINYINT UNSIGNED NOT NULL PRIMARY KEY
) ENGINE=InnoDB;

INSERT INTO digits VALUES
    (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);

-- 旧表必须有显式主键。
-- 较宽的 payload 用于频繁填满 DDL key buffer。
CREATE TABLE t_repro (
    a       INT UNSIGNED NOT NULL,
    payload VARCHAR(4000) CHARACTER SET ascii NOT NULL,
    PRIMARY KEY (a)
) ENGINE=InnoDB ROW_FORMAT=DYNAMIC;

-- 生成 500 条、每条约 4KB 的记录。
INSERT INTO t_repro(a, payload)
SELECT seq,
       REPEAT(CHAR(65 + MOD(seq, 26)), 4000)
FROM (
    SELECT d0.n
           + d1.n * 10
           + d2.n * 100
           + 1 AS seq
    FROM digits AS d0
    CROSS JOIN digits AS d1
    CROSS JOIN digits AS d2
) AS numbers
WHERE seq <= 500
ORDER BY seq DESC;

SELECT COUNT(*) AS rows_before_alter
FROM t_repro;

-- 关键操作：
-- 1. 重建聚簇索引；
-- 2. 新增 AUTO_INCREMENT 列；
-- 3. 新主键由新增列组成；
-- 4. 生成的 id 按旧主键扫描顺序递增，因此命中 skip_pk_sort。
ALTER TABLE t_repro
    DROP PRIMARY KEY,
    ADD COLUMN id BIGINT UNSIGNED NOT NULL AUTO_INCREMENT,
    ADD PRIMARY KEY (id),
    AUTO_INCREMENT = 1,
    ALGORITHM = INPLACE,
    LOCK = SHARED;

-- 正常情况下，500 行应只消费 500 个自增值：
--   MIN(id) = 1
--   MAX(id) = 500
--   missing_sequence_values = 0
--
-- 存在该问题时：
--   MAX(id) > 500
--   missing_sequence_values > 0
SELECT
    COUNT(*) AS row_count,
    COUNT(DISTINCT id) AS distinct_id_count,
    MIN(id) AS min_id,
    MAX(id) AS max_id,
    MAX(id) - MIN(id) + 1 - COUNT(*) AS missing_sequence_values
FROM t_repro;

-- 输出每一段丢失的自增值。
WITH ordered_ids AS (
    SELECT
        id,
        LAG(id) OVER (ORDER BY id) AS previous_id
    FROM t_repro
)
SELECT
    previous_id + 1 AS missing_from,
    id - 1 AS missing_to,
    id - previous_id - 1 AS missing_count
FROM ordered_ids
WHERE previous_id IS NOT NULL
  AND id > previous_id + 1
ORDER BY missing_from;

-- 查看部分相邻记录，可以直接观察 id 跳号。
WITH ordered_rows AS (
    SELECT
        id,
        a,
        LAG(id) OVER (ORDER BY id) AS previous_id
    FROM t_repro
)
SELECT previous_id, id, a
FROM ordered_rows
WHERE previous_id IS NOT NULL
  AND id > previous_id + 1
ORDER BY id
LIMIT 20;

-- 验证 ALTER 后保存的 AUTO_INCREMENT 计数器。
SHOW CREATE TABLE t_repro;

-- 再插入一行，观察实际分配的下一个 ID。
INSERT INTO t_repro(a, payload)
VALUES (1000000, 'after alter');

SELECT id AS id_allocated_after_alter
FROM t_repro
WHERE a = 1000000;

-- 如需清理，执行：
-- DROP DATABASE repro_skip_pk_sort_autoinc;
```

rows in primary:
```
mysql> select id from t_repro;
+-----+
| id  |
+-----+
|   1 |
|   2 |
|   3 |
|   4 |
|   5 |
|   6 |
|   7 |
|   8 |
|   9 |
|  10 |
|  11 |
|  12 |
|  13 |
|  14 |
|  15 |
|  16 |
|  17 |
|  18 |
|  19 |
|  20 |
|  21 |
|  22 |
|  23 |
|  24 |
|  25 |
|  26 |
|  27 |
|  28 |
|  29 |
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| 497 |
| 498 |
| 499 |
| 500 |
| 501 |
| 502 |
| 503 |
| 504 |
+-----+
501 rows in set (0.00 sec)
```

rows in replica:
```
mysql> select id from t_repro;
+-----+
| id  |
+-----+
|   1 |
|   2 |
|   3 |
|   4 |
|   5 |
|   6 |
|   7 |
|   8 |
|   9 |
|  10 |
|  11 |
|  12 |
|  13 |
|  15 |
|  16 |
|  17 |
|  18 |
|  19 |
|  20 |
|  21 |
|  22 |
|  23 |
|  24 |
|  25 |
|  26 |
|  27 |
|  29 |
|  30 |
|  31 |
|  32 |
|  33 |
|  34 |
|  35 |
|  36 |
|  37 |
|  38 |
|  39 |
|  40 |
|  41 |
|  43 |
|  44 |
|  45 |
|  46 |
|  47 |
|  48 |
|  49 |
|  50 |
|  51 |
|  52 |
|  53 |
|  54 |
|  55 |
|  57 |
|  58 |
|  59 |
|  60 |
|  61 |
|  62 |
|  63 |
|  64 |
|  65 |
|  66 |
|  67 |
|  68 |
|  69 |
|  71 |
|  72 |
|  73 |
|  74 |
|  75 |
|  76 |
|  77 |
|  78 |
|  79 |
|  80 |
|  81 |
|  82 |
|  83 |
|  85 |
|  86 |
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|  91 |
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|  96 |
|  97 |
|  99 |
| 100 |
| 101 |
| 102 |
| 103 |
| 104 |
| 105 |
| 106 |
| 107 |
| 108 |
| 109 |
| 110 |
| 111 |
| 113 |
| 114 |
| 115 |
| 116 |
| 117 |
| 118 |
| 119 |
| 120 |
| 121 |
| 122 |
| 123 |
| 124 |
| 125 |
| 127 |
| 128 |
| 129 |
| 130 |
| 131 |
| 132 |
| 133 |
| 134 |
| 135 |
| 136 |
| 137 |
| 138 |
| 139 |
| 141 |
| 142 |
| 143 |
| 144 |
| 145 |
| 146 |
| 147 |
| 148 |
| 149 |
| 150 |
| 151 |
| 152 |
| 153 |
| 155 |
| 156 |
| 157 |
| 158 |
| 159 |
| 160 |
| 161 |
| 162 |
| 163 |
| 164 |
| 165 |
| 166 |
| 167 |
| 169 |
| 170 |
| 171 |
| 172 |
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| 176 |
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| 185 |
| 186 |
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| 207 |
| 208 |
| 209 |
| 211 |
| 212 |
| 213 |
| 214 |
| 215 |
| 216 |
| 217 |
| 218 |
| 219 |
| 220 |
| 221 |
| 222 |
| 223 |
| 225 |
| 226 |
| 227 |
| 228 |
| 229 |
| 230 |
| 231 |
| 232 |
| 233 |
| 234 |
| 235 |
| 236 |
| 237 |
| 239 |
| 240 |
| 241 |
| 242 |
| 243 |
| 244 |
| 245 |
| 246 |
| 247 |
| 248 |
| 249 |
| 250 |
| 251 |
| 253 |
| 254 |
| 255 |
| 256 |
| 257 |
| 258 |
| 259 |
| 260 |
| 261 |
| 262 |
| 263 |
| 264 |
| 265 |
| 267 |
| 268 |
| 269 |
| 270 |
| 271 |
| 272 |
| 273 |
| 274 |
| 275 |
| 276 |
| 277 |
| 278 |
| 279 |
| 281 |
| 282 |
| 283 |
| 284 |
| 285 |
| 286 |
| 287 |
| 288 |
| 289 |
| 290 |
| 291 |
| 292 |
| 293 |
| 295 |
| 296 |
| 297 |
| 298 |
| 299 |
| 300 |
| 301 |
| 302 |
| 303 |
| 304 |
| 305 |
| 306 |
| 307 |
| 309 |
| 310 |
| 311 |
| 312 |
| 313 |
| 314 |
| 315 |
| 316 |
| 317 |
| 318 |
| 319 |
| 320 |
| 321 |
| 323 |
| 324 |
| 325 |
| 326 |
| 327 |
| 328 |
| 329 |
| 330 |
| 331 |
| 332 |
| 333 |
| 334 |
| 335 |
| 337 |
| 338 |
| 339 |
| 340 |
| 341 |
| 342 |
| 343 |
| 344 |
| 345 |
| 346 |
| 347 |
| 348 |
| 349 |
| 351 |
| 352 |
| 353 |
| 354 |
| 355 |
| 356 |
| 357 |
| 358 |
| 359 |
| 360 |
| 361 |
| 362 |
| 363 |
| 365 |
| 366 |
| 367 |
| 368 |
| 369 |
| 370 |
| 371 |
| 372 |
| 373 |
| 374 |
| 375 |
| 376 |
| 377 |
| 379 |
| 380 |
| 381 |
| 382 |
| 383 |
| 384 |
| 385 |
| 386 |
| 387 |
| 388 |
| 389 |
| 390 |
| 391 |
| 393 |
| 394 |
| 395 |
| 396 |
| 397 |
| 398 |
| 399 |
| 400 |
| 401 |
| 402 |
| 403 |
| 404 |
| 405 |
| 407 |
| 408 |
| 409 |
| 410 |
| 411 |
| 412 |
| 413 |
| 414 |
| 415 |
| 416 |
| 417 |
| 418 |
| 419 |
| 421 |
| 422 |
| 423 |
| 424 |
| 425 |
| 426 |
| 427 |
| 428 |
| 429 |
| 430 |
| 431 |
| 432 |
| 433 |
| 435 |
| 436 |
| 437 |
| 438 |
| 439 |
| 440 |
| 441 |
| 442 |
| 443 |
| 444 |
| 445 |
| 446 |
| 447 |
| 449 |
| 450 |
| 451 |
| 452 |
| 453 |
| 454 |
| 455 |
| 456 |
| 457 |
| 458 |
| 459 |
| 460 |
| 461 |
| 463 |
| 464 |
| 465 |
| 466 |
| 467 |
| 468 |
| 469 |
| 470 |
| 471 |
| 472 |
| 473 |
| 474 |
| 475 |
| 477 |
| 478 |
| 479 |
| 480 |
| 481 |
| 482 |
| 483 |
| 484 |
| 485 |
| 486 |
| 487 |
| 488 |
| 489 |
| 491 |
| 492 |
| 493 |
| 494 |
| 495 |
| 496 |
| 497 |
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| 500 |
| 501 |
| 502 |
| 503 |
| 504 |
| 505 |
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| 526 |
| 527 |
| 528 |
| 529 |
| 530 |
| 531 |
| 533 |
| 534 |
| 535 |
| 536 |
| 537 |
| 538 |
+-----+
501 rows in set (0.01 sec)
```

4. Insert a new row in primary and replication error.

mysql> INSERT INTO t_repro (a, payload) VALUES (42, 'hello_tdsql');

Suggested fix:
none