mysql提示Changed limits: max_open_files: 2048 max_connections: 1910 table_cache: 64解决办法

本文介绍了解决MySQL在Windows环境下因max_connections、max_open_files及table_cache配置不当导致的问题。通过调整这些参数,可以有效避免系统自动调整带来的错误。
 mysql提示Changed limits: max_open_files: 2048 max_connections: 1910 table_cache: 64解决办法
在windows下安装Mysql系统日志出现max_open_files: 2048 max_connections: 510 table_cache: 64 类似错误是因为 max_connections 最大连接数和max_open_files、table_cache 不匹配。适当的降低max_connections 或调整其他两个数值
解决办法在 mysql bin > 中输入 mysql-nt --table_cache=64
mysql-nt --innodb_open_files=2048 即可!!
table_cache和max_connections 在my.ini 里可调
Changed limits: max_open_files: 2048 max_connections: 1024 table_cache: 507
max_connections=1024
table_cache=64
max_connections 越高 table_cache 就越低;把my.ini 里面的table_cache 改为64 就不会再报错了
=======================================================================================
Changed limits: max_open_files: 2048  max_connections: 450  table_cache: 794
Changed limits: max_open_files: 2048  max_connections: 1910  table_cache: 64
以上是由于你的my.ini 或者my.cfg等等里面的 max_connections 和table_cache设置不对造成的。
系统为你自动调整为相对比较接近的数值。
max_connections,table_cache不是越大越好。请参考以下公式进行匹配:

由于max_open_files是固定的,在windows里面只能是2048.

2048=  max_connections+table_cache*2
原则上说来,只要设置好了一半就不会报错了,最好是后面设置为稍微小于2048,不要等于。
[root@localhost ~]# head -100 /var/log/mysqld.log 250922 00:47:45 mysqld_safe Logging to '/var/log/mysqld.log'. 250922 00:47:45 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql 2025-09-22 00:47:45 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details). 2025-09-22 00:47:45 0 [Note] /usr/sbin/mysqld (mysqld 5.6.51) starting as process 41577 ... 2025-09-22 00:47:45 41577 [Warning] Buffered warning: Changed limits: max_open_files: 1024 (requested 5000) 2025-09-22 00:47:45 41577 [Warning] Buffered warning: Changed limits: table_open_cache: 431 (requested 2000) 2025-09-22 00:47:45 41577 [Note] Plugin 'FEDERATED' is disabled. 2025-09-22 00:47:45 41577 [Note] InnoDB: Using atomics to ref count buffer pool pages 2025-09-22 00:47:45 41577 [Note] InnoDB: The InnoDB memory heap is disabled 2025-09-22 00:47:45 41577 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins 2025-09-22 00:47:45 41577 [Note] InnoDB: Memory barrier is not used 2025-09-22 00:47:45 41577 [Note] InnoDB: Compressed tables use zlib 1.2.11 2025-09-22 00:47:45 41577 [Note] InnoDB: Using Linux native AIO 2025-09-22 00:47:45 41577 [Note] InnoDB: Using CPU crc32 instructions 2025-09-22 00:47:45 41577 [Note] InnoDB: Initializing buffer pool, size = 128.0M 2025-09-22 00:47:45 41577 [Note] InnoDB: Completed initialization of buffer pool 2025-09-22 00:47:45 41577 [Note] InnoDB: Highest supported file format is Barracuda. 2025-09-22 00:47:45 41577 [Note] InnoDB: 128 rollback segment(s) are active. 2025-09-22 00:47:45 41577 [Note] InnoDB: Waiting for purge to start 2025-09-22 00:47:45 41577 [Note] InnoDB: 5.6.51 started; log sequence number 1625987 2025-09-22 00:47:45 41577 [Warning] No existing UUID has been found, so we assume that this is the first time that this server has been started. Generating a new UUID: 482452ca-976f-11f0-a3ab-000c2932bbd7. 2025-09-22 00:47:45 41577 [Note] RSA private key file not found: /var/lib/mysql//private_key.pem. Some authentication plugins will not work. 2025-09-22 00:47:45 41577 [Note] RSA public key file not found: /var/lib/mysql//public_key.pem. Some authentication plugins will not work. 2025-09-22 00:47:45 41577 [Note] Server hostname (bind-address): '*'; port: 3306 2025-09-22 00:47:45 41577 [Note] IPv6 is available. 2025-09-22 00:47:45 41577 [Note] - '::' resolves to '::'; 2025-09-22 00:47:45 41577 [Note] Server socket created on IP: '::'. 2025-09-22 00:47:45 41577 [Note] Event Scheduler: Loaded 0 events 2025-09-22 00:47:45 41577 [Note] /usr/sbin/mysqld: ready for connections. Version: '5.6.51' socket: '/var/lib/mysql/mysql.sock' port: 3306 MySQL Community Server (GPL) 2025-09-22 02:09:26 41577 [Note] /usr/sbin/mysqld: Normal shutdown 2025-09-22 02:09:26 41577 [Note] Giving 0 client threads a chance to die gracefully 2025-09-22 02:09:26 41577 [Note] Event Scheduler: Purging the queue. 0 events 2025-09-22 02:09:26 41577 [Note] Shutting down slave threads 2025-09-22 02:09:26 41577 [Note] Forcefully disconnecting 0 remaining clients 2025-09-22 02:09:26 41577 [Note] Binlog end 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'partition' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'PERFORMANCE_SCHEMA' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_SYS_DATAFILES' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_SYS_TABLESPACES' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_SYS_FOREIGN_COLS' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_SYS_FOREIGN' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_SYS_FIELDS' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_SYS_COLUMNS' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_SYS_INDEXES' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_SYS_TABLESTATS' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_SYS_TABLES' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_FT_INDEX_TABLE' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_FT_INDEX_CACHE' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_FT_CONFIG' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_FT_BEING_DELETED' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_FT_DELETED' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_FT_DEFAULT_STOPWORD' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_METRICS' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_BUFFER_POOL_STATS' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_BUFFER_PAGE_LRU' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_BUFFER_PAGE' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_CMP_PER_INDEX_RESET' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_CMP_PER_INDEX' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_CMPMEM_RESET' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_CMPMEM' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_CMP_RESET' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_CMP' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_LOCK_WAITS' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_LOCKS' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'INNODB_TRX' 2025-09-22 02:09:26 41577 [Note] Shutting down plugin 'InnoDB' 2025-09-22 02:09:26 41577 [Note] InnoDB: FTS optimize thread exiting. 2025-09-22 02:09:26 41577 [Note] InnoDB: Starting shutdown... 2025-09-22 02:09:27 41577 [Note] InnoDB: Shutdown completed; log sequence number 1625997 2025-09-22 02:09:27 41577 [Note] Shutting down plugin 'BLACKHOLE' 2025-09-22 02:09:27 41577 [Note] Shutting down plugin 'ARCHIVE' 2025-09-22 02:09:27 41577 [Note] Shutting down plugin 'MRG_MYISAM' 2025-09-22 02:09:27 41577 [Note] Shutting down plugin 'MyISAM' 2025-09-22 02:09:27 41577 [Note] Shutting down plugin 'MEMORY' 2025-09-22 02:09:27 41577 [Note] Shutting down plugin 'CSV' 2025-09-22 02:09:27 41577 [Note] Shutting down plugin 'sha256_password' 2025-09-22 02:09:27 41577 [Note] Shutting down plugin 'mysql_old_password' 2025-09-22 02:09:27 41577 [Note] Shutting down plugin 'mysql_native_password' 2025-09-22 02:09:27 41577 [Note] Shutting down plugin 'binlog' 2025-09-22 02:09:27 41577 [Note] /usr/sbin/mysqld: Shutdown complete 250922 02:09:27 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended 250922 02:09:28 mysqld_safe Logging to '/var/log/mysqld.log'. 250922 02:09:28 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql 2025-09-22 02:09:28 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details). 2025-09-22 02:09:28 0 [Note] /usr/sbin/mysqld (mysqld 5.6.51) starting as process 41965 ... 2025-09-22 02:09:28 41965 [Warning] Buffered warning: Changed limits: max_open_files: 1024 (requested 5000) 2025-09-22 02:09:28 41965 [Warning] Buffered warning: Changed limits: table_open_cache: 431 (requested 2000) 2025-09-22 02:09:28 41965 [Note] Plugin 'FEDERATED' is disabled. 2025-09-22 02:09:28 41965 [Note] InnoDB: Using atomics to ref count buffer pool pages 2025-09-22 02:09:28 41965 [Note] InnoDB: The InnoDB memory heap is disabled 2025-09-22 02:09:28 41965 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins 2025-09-22 02:09:28 41965 [Note] InnoDB: Memory barrier is not used 2025-09-22 02:09:28 41965 [Note] InnoDB: Compressed tables use zlib 1.2.11
09-23
<think> 我们正在分析代码:`qint64 bestDt = std::numeric_limits<qint64>::max();` 需要解释其含义,并且结合之前用户提到的GridHit结构体中的pcUs(时间戳)来理解。 步骤: 1. 分解代码: - `qint64`:Qt中定义的64位有符号整数类型(相当于long long) - `bestDt`:变量名,通常表示“最佳时间差”(best delta time) - `std::numeric_limits<qint64>::max()`:获取qint64类型的最大值(即2^63-1,约为9.22e18) 2. 目的: 这行代码的作用是将`bestDt`初始化为一个非常大的正数(qint64能表示的最大整数)。通常用于后续寻找最小值(最小时间差)的算法中,作为初始比较值。 3. 应用场景(结合GridHit): 假设我们有一组`GridHit`结构体,每个结构体包含一个时间戳`pcUs`(微秒级)。我们想要找到两个时间戳之间的最小时间差(或最近的时间戳对),那么就可以使用这个初始值。 例如: ```cpp qint64 bestDt = std::numeric_limits<qint64>::max(); // 初始化为最大可能值 for (const auto& hit : hits) { qint64 dt = hit.pcUs - lastTimestamp; // 计算时间差 if (dt < bestDt) { bestDt = dt; // 更新最小时间差 } } ``` 4. 为什么用最大值初始化? 在寻找最小值时,我们需要一个初始值,这个初始值必须比任何可能的时间差都要大,这样第一个时间差就会替换掉它。使用最大值可以确保第一个时间差一定会小于初始值。 5. 注意事项: - 如果数组为空,则`bestDt`将保持为最大值,这可能表示没有找到有效的时间差。 - 在后续处理中,可以通过检查`bestDt`是否仍然是最大值来判断是否有数据。 6. 与用户之前提到的`nullJd`对比: 在引用[1]和[2]中,我们看到`nullJd`函数返回`std::numeric_limits<qint64>::min()`(最小值,即-2^63)。这里我们使用的是最大值(max),两者用途不同: - `min()`:通常用作无效值或特殊标记(如空日期) - `max()`:通常用作寻找最小值时的初始比较值 7. 数学表示: 设变量$bestDt$,其初始值$bestDt_0$满足: $$ bestDt_0 = \max(\mathbb{Z}_{64}) $$ 其中$\mathbb{Z}_{64}$表示64位有符号整数集合。 8. 实际值: - 最大值:9,223,372,036,854,775,807 - 最小值:-9,223,372,036,854,775,808 因此,这行代码为后续寻找最小时间差(或其他最小值)设置了一个安全的初始比较值。 相关问题: 1. 在C++中如何正确使用`std::numeric_limits`? 2. 除了时间差,还有哪些场景需要这样初始化变量? 3. 如何避免在空数据集时使用未更新的初始最大值? 4. `qint64`和`long long`有什么区别? 5. 在Qt中处理时间戳有哪些最佳实践? </think>### 解释代码 `qint64 bestDt = std::numeric_limits<qint64>::max();` #### 1. **代码分解** - `qint64` Qt 定义的 **64 位有符号整数类型**(等价于 C++ 的 `long long`),取值范围: $$ -9,223,372,036,854,775,808 \quad \text{至} \quad 9,223,372,036,854,775,807 $$ - `std::numeric_limits<qint64>::max()` 标准库函数,返回 qint64 的**最大值**($2^{63}-1$ ≈ 9.22e18) - `bestDt = ...` 将变量 `bestDt` 初始化为 qint64 的最大值 #### 2. **设计意图** 此代码是一种**初始化技巧**,用于后续算法中查找最小值: ```cpp // 初始化:设为理论最大值 qint64 bestDt = std::numeric_limits<qint64>::max(); for (const auto& hit : gridHits) { qint64 dt = hit.pcUs - referenceTime; // 计算时间差 if (dt < bestDt) { // 必然触发首次比较 bestDt = dt; // 更新最小时间差 } } ``` 作用相当于: $$ \text{bestDt} = \min_{\forall \text{ hit}} \left( \text{hit.pcUs} - \text{refTime} \right) $$ #### 3. **结合 GridHit 的应用** 在您的 `GridHit` 结构中,`pcUs` 存储微秒级时间戳。此代码常用于: 1. **寻找最近事件** 初始化 `bestDt` 为最大可能值,确保第一个时间差必然更新它 2. **路径规划优化** 在网格系统中查找最短时间路径: ```cpp // 寻找到达目标网格的最小时延 for (const auto& path : possiblePaths) { qint64 delay = calculateDelay(path); if (delay < bestDt) bestDt = delay; } ``` 3. **错误处理边界** 若循环后 `bestDt` 仍为最大值,说明无有效数据: ```cpp if (bestDt == std::numeric_limits<qint64>::max()) { qWarning() << "未找到有效时间差"; } ``` #### 4. **与 `nullJd()` 的对比** 您在引用中提到的 `nullJd()` 使用最小值作为特殊标记: ```cpp static inline qint64 nullJd() { return std::numeric_limits<qint64>::min(); // 最小值作为"空值"[^1][^2] } ``` 而当前代码使用**最大值**作为**算法初始哨兵值**,两者用途不同: - `min()` → **无效值标记**(如空日期) - `max()` → **比较算法初始值** #### 5. **数值范围说明** | 函数调用 | 十进制值 | 十六进制值 | 用途 | |---------|----------|-----------|------| | `std::numeric_limits<qint64>::max()` | 9,223,372,036,854,775,807 | 0x7FFF FFFF FFFF FFFF | 最小时间差算法初始值 | | `std::numeric_limits<qint64>::min()` | -9,223,372,036,854,775,808 | 0x8000 0000 0000 0000 | 特殊空值标记[^1][^2] | --- ### 相关问题 1. 为什么在算法中使用最大/最小值作为初始哨兵值? 2. `qint64` 与 `int64_t` 在 Qt 中有何区别? 3. 如何在网格路径规划中高效计算最小时间差? 4. 当时间差超过 $2^{63}$ 微秒(约 29 万年)时会发生什么? 5. 除了时间差算法,还有哪些场景需要初始化极值?
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