慎重升级到 MySQL 8.0.38 及更高版本（文末附规避风险办法）

前几天，Percona 资深工程师 Marco Tusa 爆料，升级到 MySQL 8.0.38 版本后，当实例中的表个数超过一万个，实例重启后会发生 Crash 而失败，即便是重启时加上 validate_tablespace_paths=OFF 也不行。

这个问题在 >= 8.0.38 版本中存在，包括 8.4.1 和 9.0.0。

详细复现过程参见：https://perconadev.atlassian.net/browse/PS-9306。

我用 MySQL 9.0.0 版本测试：

-- 创建一个最简单的表，并写入数据
> CREATE DATABASE test;
> USE test;
> CREATE TABLE t_1 (
  `id` int NOT NULL,
  PRIMARY KEY (`id`)
);

> INSERT INTO t_1 SELECT 1;

然后反复创建类似上面的表，表个数达到 1 万。

> SELECT COUNT(*) FROM information_schema.tables WHERE TABLE_SCHEMA ='test';
+----------+
| count(*) |
+----------+
|    10000 |
+----------+

之后重启实例，就能看到日志里有类似下面的内容，启动失败：

[Note] [MY-012207] [InnoDB] Using 2 threads to scan 10002 tablespace files
[Note] [MY-012200] [InnoDB] Thread# 0 - Checked 876/10002 files
...
[Note] [MY-012201] [InnoDB] Checked 10002 files
[Note] [MY-012208] [InnoDB] Completed space ID check of 10004 files.
...
2024-07-12T06:48:14Z UTC - mysqld got signal 11 ;
Signal SIGSEGV (Address not mapped to object) at address 0x508
Most likely, you have hit a bug, but this error can also be caused by malfunctioning hardware.
BuildID[sha1]=7f06a4743d7801096bd81bc999201fdbca43a12c
Thread pointer: 0x0
Attempting backtrace. You can use the following information to find out
where mysqld died. If you see no messages after this, something went
terribly wrong...
stack_bottom = 0 thread_stack 0x100000

[root@db160 mysql-9.0.0-linux-glibc2.17-x86_64-minimal]#  #0 0x103f726 <unknown>
 #1 0x103fa8c <unknown>
 #2 0x7f18f666ac1f <unknown> at sysdeps/unix/sysv/linux/x86_64/sigaction.c:0
 #3 0x218a7be <unknown>
 #4 0x21705a7 <unknown>
 #5 0x2b1d263 <unknown>
 #6 0x7f18f6660179 start_thread at /usr/src/debug/glibc-2.28/nptl/pthread_create.c:479
 #7 0x7f18f4811dc2 <unknown> at sysdeps/unix/sysv/linux/x86_64/clone.S:95
 #8 0xffffffffffffffff <unknown>
The manual page at http://dev.mysql.com/doc/mysql/en/crashing.html contains
information that should help you find out what is causing the crash.

确实挺拉胯的。

另外，还是有办法可以规避的，也就是采用 共享/通用 表空间方案，例如：

-- 1. 共享表空间方案
> SET GLOBAL innodb_file_per_table = 0;
> CREATE TABLE ...;

-- 2. 通用表空间方案
> CREATE TABLESPACE test ADD DATAFILE 'test.ibd';
> CREATE TABLE t_1(...) TABLESPACE=test;

这个 Bug 很 low，但这个问题很小，也很容易规避

慎重升级到 MySQL 8.0.38 及更高版本（文末附规避风险办法）

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