如何杀掉空闲事务
本文内容遵从CC版权协议, 可以随意转载, 但必须以超链接形式标明文章原始出处和作者信息及版权声明网址: http://www.penglixun.com/tech/database/how_to_kill_idle_trx.html 我们经常遇到一个情况，就是网络断开或程序Bug导致COMMIT/ROLLBACK语句没有传到数
本文内容遵从CC版权协议, 可以随意转载, 但必须以超链接形式标明文章原始出处和作者信息及版权声明网址: http://www.penglixun.com/tech/database/how_to_kill_idle_trx.html
我们经常遇到一个情况，就是网络断开或程序Bug导致COMMIT/ROLLBACK语句没有传到数据库，也没有释放线程，但是线上事务锁定等待严重，连接数暴涨，尤其在测试库这种情况很多，线上也偶有发生，于是想为MySQL增加一个杀掉空闲事务的功能。
那么如何实现呢，通过MySQL Server层有很多不确定因素，最保险还是在存储引擎层实现，我们用的几乎都是InnoDB/XtraDB，所以就基于Percona来修改了，Oracle版的MySQL也可以照着修改。
需求：
1. 一个事务启动，如果事务内最后一个语句执行完超过一个时间(innodb_idle_trx_timeout)，就应该关闭链接。
2. 如果事务是纯读事务，因为不加锁，所以无害，不需要关闭，保持即可。
虽然这个思路被Percona的指出Alexey Kopytov可能存在“Even though SELECT queries do not place row locks by default (there are exceptions), they can still block undo log records from being purged.”的问题，但是我们确实有场景SELECT是绝对不能kill的，除非之后的INSERT/UPDATE/DELETE发生了，所以我根据我们的业务特点来修改。
跟Percona的Yasufumi Kinoshita和Alexey Kopytov提出过纯SELECT事务不应被kill，但通过一个参数控制的方案还没有被Alexey Kopytov接受，作为通用处理我提出了用两个变量分别控制纯读事务的空闲超时时间和有锁事务的空闲超时时间，还在等待Percona的回复，因为这个方案还在测试，就先不开放修改了，当然如果你很熟悉MYSQL源码，我提出这个思路你肯定知道怎么分成这两个参数控制了。
根据这两个需求我们来设计方法，首先想到这个功能肯定是放在InnoDB Master Thread最方便，Master Thread每秒调度一次，可以顺便检查空闲事务，然后关闭，因为在事务中操作trx->mysql_thd并不安全，所以一般来说最好在InnoDB层换成Thread ID操作，并且InnoDB中除了ha_innodb.cc，其他地方不能饮用THD，所以Master Thread中需要的线程数值，都需要在ha_innodb中计算好传递整型或布尔型返回值给master thread调用。
首先，我们要增加一个参数：idle_trx_timeout，它表示事务多久没有下一条语句发生就超时关闭。
在storage/innodb_plugin/srv/srv0srv.c的“/* plugin options */”注释下增加如下代码注册idle_trx_timeout变量。
<span style="color: #0000ff;">static</span> MYSQL_SYSVAR_LONG<span style="color: #008000;">(</span>idle_trx_timeout, srv_idle_trx_timeout, PLUGIN_VAR_RQCMDARG, <span style="color: #FF0000;">"If zero then this function no effect, if no-zero then wait idle_trx_timeout seconds this transaction will be closed"</span>, <span style="color: #FF0000;">"Seconds of Idle-Transaction timeout"</span>, <span style="color: #0000ff;">NULL</span>, <span style="color: #0000ff;">NULL</span>, <span style="color: #0000dd;">0</span>, <span style="color: #0000dd;">0</span>, <span style="color: #0000ff;">LONG_MAX</span>, <span style="color: #0000dd;">0</span><span style="color: #008000;">)</span><span style="color: #008080;">;</span>
代码往下找在innobase_system_variables结构体内加上：
MYSQL_SYSVAR<span style="color: #008000;">(</span>idle_trx_timeout<span style="color: #008000;">)</span>,
有了这个变量，我们需要在Master Thread(storage/innodb_plugin/srv/srv0srv.c )中执行检测函数查找空闲事务。在loop循环的if (sync_array_print_long_waits(&waiter, &sema)判断后加上这段判断
<span style="color: #0000ff;">if</span> <span style="color: #008000;">(</span>srv_idle_trx_timeout <span style="color: #000040;">&&</span> trx_sys<span style="color: #008000;">)</span> <span style="color: #008000;">{</span>
trx_t<span style="color: #000040;">*</span> trx<span style="color: #008080;">;</span>
<span style="color: #0000ff;">time_t</span> now<span style="color: #008080;">;</span>
rescan_idle<span style="color: #008080;">:</span>
now <span style="color: #000080;">=</span> <span style="color: #0000dd;">time</span><span style="color: #008000;">(</span><span style="color: #0000ff;">NULL</span><span style="color: #008000;">)</span><span style="color: #008080;">;</span>
mutex_enter<span style="color: #008000;">(</span><span style="color: #000040;">&</span>kernel_mutex<span style="color: #008000;">)</span><span style="color: #008080;">;</span>
trx <span style="color: #000080;">=</span> UT_LIST_GET_FIRST<span style="color: #008000;">(</span>trx_sys<span style="color: #000040;">-</span><span style="color: #000080;">></span>mysql_trx_list<span style="color: #008000;">)</span><span style="color: #008080;">;</span> <span style="color: #339900;"># 从当前事务列表里获取第一个事务</span>
<span style="color: #0000ff;">while</span> <span style="color: #008000;">(</span>trx<span style="color: #008000;">)</span> <span style="color: #008000;">{</span> <span style="color: #339900;"># 依次循环每个事务进行检查</span>
<span style="color: #0000ff;">if</span> <span style="color: #008000;">(</span>trx<span style="color: #000040;">-</span><span style="color: #000080;">></span>conc_state <span style="color: #000080;">==</span> TRX_ACTIVE
<span style="color: #000040;">&&</span> trx<span style="color: #000040;">-</span><span style="color: #000080;">></span>mysql_thd
<span style="color: #000040;">&&</span> innobase_thd_is_idle<span style="color: #008000;">(</span>trx<span style="color: #000040;">-</span><span style="color: #000080;">></span>mysql_thd<span style="color: #008000;">)</span><span style="color: #008000;">)</span> <span style="color: #008000;">{</span> <span style="color: #339900;"># 如果事务还活着并且它的状态时空闲的</span>
ib_int64_t start_time <span style="color: #000080;">=</span> innobase_thd_get_start_time<span style="color: #008000;">(</span>trx<span style="color: #000040;">-</span><span style="color: #000080;">></span>mysql_thd<span style="color: #008000;">)</span><span style="color: #008080;">;</span> <span style="color: #339900;"># 获取线程最后一个语句的开始时间</span>
ulong thd_id <span style="color: #000080;">=</span> innobase_thd_get_thread_id<span style="color: #008000;">(</span>trx<span style="color: #000040;">-</span><span style="color: #000080;">></span>mysql_thd<span style="color: #008000;">)</span><span style="color: #008080;">;</span> <span style="color: #339900;">#获取线程ID，因为存储引擎内直接操作THD不安全</span>
<span style="color: #0000ff;">if</span> <span style="color: #008000;">(</span>trx<span style="color: #000040;">-</span><span style="color: #000080;">></span>last_stmt_start <span style="color: #000040;">!</span><span style="color: #000080;">=</span> start_time<span style="color: #008000;">)</span> <span style="color: #008000;">{</span> <span style="color: #339900;"># 如果事务最后语句起始时间不等于线程最后语句起始时间说明事务是新起的</span>
trx<span style="color: #000040;">-</span><span style="color: #000080;">></span>idle_start <span style="color: #000080;">=</span> now<span style="color: #008080;">;</span> <span style="color: #339900;"># 更新事务的空闲起始时间</span>
trx<span style="color: #000040;">-</span><span style="color: #000080;">></span>last_stmt_start <span style="color: #000080;">=</span> start_time<span style="color: #008080;">;</span> <span style="color: #339900;"># 更新事务的最后语句起始时间</span>
<span style="color: #008000;">}</span> <span style="color: #0000ff;">else</span> <span style="color: #0000ff;">if</span> <span style="color: #008000;">(</span><span style="color: #0000dd;">difftime</span><span style="color: #008000;">(</span>now, trx<span style="color: #000040;">-</span><span style="color: #000080;">></span>idle_start<span style="color: #008000;">)</span> <span style="color: #339900;"># 如果事务不是新起的，已经执行了一部分则判断空闲时间有多长了</span>
<span style="color: #000080;">></span> srv_idle_trx_timeout<span style="color: #008000;">)</span> <span style="color: #008000;">{</span> <span style="color: #339900;"># 如果空闲时间超过阈值则杀掉链接</span>
<span style="color: #ff0000; font-style: italic;">/* kill the session */</span>
mutex_exit<span style="color: #008000;">(</span><span style="color: #000040;">&</span>kernel_mutex<span style="color: #008000;">)</span><span style="color: #008080;">;</span>
thd_kill<span style="color: #008000;">(</span>thd_id<span style="color: #008000;">)</span><span style="color: #008080;">;</span> <span style="color: #339900;"># 杀链接</span>
<span style="color: #0000ff;">goto</span> rescan_idle<span style="color: #008080;">;</span>
<span style="color: #008000;">}</span>
<span style="color: #008000;">}</span>
trx <span style="color: #000080;">=</span> UT_LIST_GET_NEXT<span style="color: #008000;">(</span>mysql_trx_list, trx<span style="color: #008000;">)</span><span style="color: #008080;">;</span> <span style="color: #339900;"># 检查下一个事务</span>
<span style="color: #008000;">}</span>
mutex_exit<span style="color: #008000;">(</span><span style="color: #000040;">&</span>kernel_mutex<span style="color: #008000;">)</span><span style="color: #008080;">;</span>
<span style="color: #008000;">}</span>其中trx中的变量是新加的，在storage/innodb_plugin/include/trx0trx.h的trx_truct加上需要的变量：
<span style="color: #0000ff;">struct</span> trx_struct<span style="color: #008000;">{</span>
...
<span style="color: #0000ff;">time_t</span> idle_start<span style="color: #008080;">;</span>
ib_int64_t last_stmt_start<span style="color: #008080;">;</span>
...
<span style="color: #008000;">}</span>这里有几个函数是自定义的：
ibool innobase_thd_is_idle<span style="color: #008000;">(</span><span style="color: #0000ff;">const</span> <span style="color: #0000ff;">void</span><span style="color: #000040;">*</span> thd<span style="color: #008000;">)</span><span style="color: #008080;">;</span> ib_int64_t innobase_thd_get_start_time<span style="color: #008000;">(</span><span style="color: #0000ff;">const</span> <span style="color: #0000ff;">void</span><span style="color: #000040;">*</span> thd<span style="color: #008000;">)</span><span style="color: #008080;">;</span> ulong innobase_thd_get_thread_id<span style="color: #008000;">(</span><span style="color: #0000ff;">const</span> <span style="color: #0000ff;">void</span><span style="color: #000040;">*</span> thd<span style="color: #008000;">)</span><span style="color: #008080;">;</span>
这些函数在ha_innodb.cc中实现，需要在storage/innodb_plugin/srv/srv0srv.c头文件定义下加上这些函数的引用形势。
然后在storage/innodb_plugin/handler/ha_innodb.cc 中定义这些函数的实现：
<span style="color: #0000ff;">extern</span> <span style="color: #FF0000;">"C"</span>
ibool
innobase_thd_is_idle<span style="color: #008000;">(</span>
<span style="color: #0000ff;">const</span> <span style="color: #0000ff;">void</span><span style="color: #000040;">*</span> thd<span style="color: #008000;">)</span> <span style="color: #ff0000; font-style: italic;">/*!< in: thread handle (THD*) */</span>
<span style="color: #008000;">{</span>
<span style="color: #0000ff;">return</span><span style="color: #008000;">(</span><span style="color: #008000;">(</span><span style="color: #008000;">(</span><span style="color: #0000ff;">const</span> THD<span style="color: #000040;">*</span><span style="color: #008000;">)</span>thd<span style="color: #008000;">)</span><span style="color: #000040;">-</span><span style="color: #000080;">></span>command <span style="color: #000080;">==</span> COM_SLEEP<span style="color: #008000;">)</span><span style="color: #008080;">;</span>
<span style="color: #008000;">}</span>
<span style="color: #0000ff;">extern</span> <span style="color: #FF0000;">"C"</span>
ib_int64_t
innobase_thd_get_start_time<span style="color: #008000;">(</span>
<span style="color: #0000ff;">const</span> <span style="color: #0000ff;">void</span><span style="color: #000040;">*</span> thd<span style="color: #008000;">)</span> <span style="color: #ff0000; font-style: italic;">/*!< in: thread handle (THD*) */</span>
<span style="color: #008000;">{</span>
<span style="color: #0000ff;">return</span><span style="color: #008000;">(</span><span style="color: #008000;">(</span>ib_int64_t<span style="color: #008000;">)</span><span style="color: #008000;">(</span><span style="color: #008000;">(</span><span style="color: #0000ff;">const</span> THD<span style="color: #000040;">*</span><span style="color: #008000;">)</span>thd<span style="color: #008000;">)</span><span style="color: #000040;">-</span><span style="color: #000080;">></span>start_time<span style="color: #008000;">)</span><span style="color: #008080;">;</span>
<span style="color: #008000;">}</span>
<span style="color: #0000ff;">extern</span> <span style="color: #FF0000;">"C"</span>
ulong
innobase_thd_get_thread_id<span style="color: #008000;">(</span>
<span style="color: #0000ff;">const</span> <span style="color: #0000ff;">void</span><span style="color: #000040;">*</span> thd<span style="color: #008000;">)</span>
<span style="color: #008000;">{</span>
<span style="color: #0000ff;">return</span><span style="color: #008000;">(</span>thd_get_thread_id<span style="color: #008000;">(</span><span style="color: #008000;">(</span><span style="color: #0000ff;">const</span> THD<span style="color: #000040;">*</span><span style="color: #008000;">)</span> thd<span style="color: #008000;">)</span><span style="color: #008000;">)</span><span style="color: #008080;">;</span>
<span style="color: #008000;">}</span>还有最重要的thd_kill函数负责杀线程的，在sql/sql_class.cc中，找个地方定义这个函数：
<span style="color: #0000ff;">void</span> thd_kill<span style="color: #008000;">(</span>ulong id<span style="color: #008000;">)</span>
<span style="color: #008000;">{</span>
THD <span style="color: #000040;">*</span>tmp<span style="color: #008080;">;</span>
VOID<span style="color: #008000;">(</span>pthread_mutex_lock<span style="color: #008000;">(</span><span style="color: #000040;">&</span>LOCK_thread_count<span style="color: #008000;">)</span><span style="color: #008000;">)</span><span style="color: #008080;">;</span>
I_List_iterator<span style="color: #000080;"><</span>THD<span style="color: #000080;">></span> it<span style="color: #008000;">(</span>threads<span style="color: #008000;">)</span><span style="color: #008080;">;</span>
<span style="color: #0000ff;">while</span> <span style="color: #008000;">(</span><span style="color: #008000;">(</span>tmp<span style="color: #000080;">=</span>it<span style="color: #000040;">++</span><span style="color: #008000;">)</span><span style="color: #008000;">)</span>
<span style="color: #008000;">{</span>
<span style="color: #0000ff;">if</span> <span style="color: #008000;">(</span>tmp<span style="color: #000040;">-</span><span style="color: #000080;">></span>command <span style="color: #000080;">==</span> COM_DAEMON <span style="color: #000040;">||</span> tmp<span style="color: #000040;">-</span><span style="color: #000080;">></span>is_have_lock_thd <span style="color: #000080;">==</span> <span style="color: #0000dd;">0</span> <span style="color: #008000;">)</span> <span style="color: #339900;"># 如果是DAEMON线程和不含锁的线程就不要kill了</span>
<span style="color: #0000ff;">continue</span><span style="color: #008080;">;</span>
<span style="color: #0000ff;">if</span> <span style="color: #008000;">(</span>tmp<span style="color: #000040;">-</span><span style="color: #000080;">></span>thread_id <span style="color: #000080;">==</span> id<span style="color: #008000;">)</span>
<span style="color: #008000;">{</span>
pthread_mutex_lock<span style="color: #008000;">(</span><span style="color: #000040;">&</span>tmp<span style="color: #000040;">-</span><span style="color: #000080;">></span>LOCK_thd_data<span style="color: #008000;">)</span><span style="color: #008080;">;</span>
<span style="color: #0000ff;">break</span><span style="color: #008080;">;</span>
<span style="color: #008000;">}</span>
<span style="color: #008000;">}</span>
VOID<span style="color: #008000;">(</span>pthread_mutex_unlock<span style="color: #008000;">(</span><span style="color: #000040;">&</span>LOCK_thread_count<span style="color: #008000;">)</span><span style="color: #008000;">)</span><span style="color: #008080;">;</span>
<span style="color: #0000ff;">if</span> <span style="color: #008000;">(</span>tmp<span style="color: #008000;">)</span>
<span style="color: #008000;">{</span>
tmp<span style="color: #000040;">-</span><span style="color: #000080;">></span>awake<span style="color: #008000;">(</span>THD<span style="color: #008080;">::</span><span style="color: #007788;">KILL_CONNECTION</span><span style="color: #008000;">)</span><span style="color: #008080;">;</span>
pthread_mutex_unlock<span style="color: #008000;">(</span><span style="color: #000040;">&</span>tmp<span style="color: #000040;">-</span><span style="color: #000080;">></span>LOCK_thd_data<span style="color: #008000;">)</span><span style="color: #008080;">;</span>
<span style="color: #008000;">}</span>
<span style="color: #008000;">}</span>为了存储引擎能引用到这个函数，我们要把它定义到plugin中：
include/mysql/plugin.h和include/mysql/plugin.h中加上
<span style="color: #0000ff;">void</span> thd_kill<span style="color: #008000;">(</span><span style="color: #0000ff;">unsigned</span> <span style="color: #0000ff;">long</span> id<span style="color: #008000;">)</span><span style="color: #008080;">;</span>
如何判定线程的is_have_lock_thd值？首先在THD中加上这个变量（sql/sql_class.cc）：
<span style="color: #0000ff;">class</span> THD <span style="color: #008080;">:</span><span style="color: #0000ff;">public</span> Statement,
<span style="color: #0000ff;">public</span> Open_tables_state
<span style="color: #008000;">{</span>
....
<span style="color: #007788;">uint16</span> is_have_lock_thd<span style="color: #008080;">;</span>
....
<span style="color: #008000;">}</span>然后在SQL的必经之路mysql_execute_command拦上一刀，判断是有锁操作发生了还是事务提交或新起事务。
<span style="color: #0000ff;">switch</span> <span style="color: #008000;">(</span>lex<span style="color: #000040;">-</span><span style="color: #000080;">></span>sql_command<span style="color: #008000;">)</span> <span style="color: #008000;">{</span>
<span style="color: #0000ff;">case</span> SQLCOM_REPLACE<span style="color: #008080;">:</span>
<span style="color: #0000ff;">case</span> SQLCOM_REPLACE_SELECT<span style="color: #008080;">:</span>
<span style="color: #0000ff;">case</span> SQLCOM_UPDATE<span style="color: #008080;">:</span>
<span style="color: #0000ff;">case</span> SQLCOM_UPDATE_MULTI<span style="color: #008080;">:</span>
<span style="color: #0000ff;">case</span> SQLCOM_DELETE<span style="color: #008080;">:</span>
<span style="color: #0000ff;">case</span> SQLCOM_DELETE_MULTI<span style="color: #008080;">:</span>
<span style="color: #0000ff;">case</span> SQLCOM_INSERT<span style="color: #008080;">:</span>
<span style="color: #0000ff;">case</span> SQLCOM_INSERT_SELECT<span style="color: #008080;">:</span>
thd<span style="color: #000040;">-</span><span style="color: #000080;">></span>is_have_lock_thd <span style="color: #000080;">=</span> <span style="color: #0000dd;">1</span><span style="color: #008080;">;</span>
<span style="color: #0000ff;">break</span><span style="color: #008080;">;</span>
<span style="color: #0000ff;">case</span> SQLCOM_COMMIT<span style="color: #008080;">:</span>
<span style="color: #0000ff;">case</span> SQLCOM_ROLLBACK<span style="color: #008080;">:</span>
<span style="color: #0000ff;">case</span> SQLCOM_XA_START<span style="color: #008080;">:</span>
<span style="color: #0000ff;">case</span> SQLCOM_XA_END<span style="color: #008080;">:</span>
<span style="color: #0000ff;">case</span> SQLCOM_XA_PREPARE<span style="color: #008080;">:</span>
<span style="color: #0000ff;">case</span> SQLCOM_XA_COMMIT<span style="color: #008080;">:</span>
<span style="color: #0000ff;">case</span> SQLCOM_XA_ROLLBACK<span style="color: #008080;">:</span>
<span style="color: #0000ff;">case</span> SQLCOM_XA_RECOVER<span style="color: #008080;">:</span>
thd<span style="color: #000040;">-</span><span style="color: #000080;">></span>is_have_lock_thd <span style="color: #000080;">=</span> <span style="color: #0000dd;">0</span><span style="color: #008080;">;</span>
<span style="color: #0000ff;">break</span><span style="color: #008080;">;</span>
<span style="color: #008000;">}</span>为了尽可能兼容Percona的补丁，能引用的都引用了Percona的操作，有些函数调用是在层次太多看不下去了就简化了。
另外还有一个版本是我自己弄的，在THD中增加了一个last_sql_end_time，在do_command结束后更新last_sql_end_time，然后在事务中拿到THD查看last_sql_end_time就可以得出idle时间，Oracle版我还是建议这么做，不要去改trx_struct结构体了，那个感觉更危险。
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How to change the Microsoft Edge browser to open with 360 navigation - How to change the opening with 360 navigation
Mar 04, 2024 pm 01:50 PM
How to change the page that opens the Microsoft Edge browser to 360 navigation? It is actually very simple, so now I will share with you the method of changing the page that opens the Microsoft Edge browser to 360 navigation. Friends in need can take a look. I hope Can help everyone. Open the Microsoft Edge browser. We see a page like the one below. Click the three-dot icon in the upper right corner. Click "Settings." Click "On startup" in the left column of the settings page. Click on the three points shown in the picture in the right column (do not click "Open New Tab"), then click Edit and change the URL to "0" (or other meaningless numbers). Then click "Save". Next, select "
Can I delete the downloads folder?
Feb 19, 2024 pm 03:38 PM
Can downloads be deleted? In recent years, with the advent of the digital age, more and more digital products and services have appeared in our lives. What follows is that our demand for digital content is increasing day by day. In our daily life and work, we often need to download a variety of files, such as documents, pictures, audios, videos, etc. These downloaded files are usually saved in a folder called "downloads". However, over time we often find that,"
How to set up Cheat Engine in Chinese? Cheat Engine setting Chinese method
Mar 13, 2024 pm 04:49 PM
CheatEngine is a game editor that can edit and modify the game's memory. However, its default language is non-Chinese, which is inconvenient for many friends. So how to set Chinese in CheatEngine? Today, the editor will give you a detailed introduction to how to set up Chinese in CheatEngine. I hope it can help you. Setting method one: 1. Double-click to open the software and click "edit" in the upper left corner. 2. Then click “settings” in the option list below. 3. In the opened window interface, click "languages" in the left column
PHP PDO Tutorial: An Advanced Guide from Basics to Mastery
Feb 19, 2024 pm 06:30 PM
1. Introduction to PDO PDO is an extension library of PHP, which provides an object-oriented way to operate the database. PDO supports a variety of databases, including Mysql, postgresql, oracle, SQLServer, etc. PDO enables developers to use a unified API to operate different databases, which allows developers to easily switch between different databases. 2. PDO connects to the database. To use PDO to connect to the database, you first need to create a PDO object. The constructor of the PDO object receives three parameters: database type, host name, database username and password. For example, the following code creates an object that connects to a mysql database: $dsn="mysq
MySQL transaction processing: the difference between automatic submission and manual submission
Mar 16, 2024 am 11:33 AM
MySQL transaction processing: the difference between automatic submission and manual submission. In the MySQL database, a transaction is a set of SQL statements. Either all executions are successful or all executions fail, ensuring the consistency and integrity of the data. In MySQL, transactions can be divided into automatic submission and manual submission. The difference lies in the timing of transaction submission and the scope of control over the transaction. The following will introduce the difference between automatic submission and manual submission in detail, and give specific code examples to illustrate. 1. Automatically submit in MySQL, if it is not displayed
Which games are suitable for playing with i34150 and 1G independent graphics (which games is suitable for i34150)
Jan 05, 2024 pm 08:24 PM
What games can be played with i34150 with 1G independent graphics? Can it play small games such as LoL? GTX750 and GTX750TI are very suitable graphics card choices. If you just play some small games or not play games, it is recommended to use the i34150 integrated graphics card. Generally speaking, the price difference between graphics cards and processors is not very big, so it is important to choose a reasonable combination. If you need 2G of video memory, it is recommended to choose GTX750TI; if you only need 1G of video memory, just choose GTX750. GTX750TI can be seen as an enhanced version of GTX750, with overclocking capabilities. Which graphics card can be paired with i34150 depends on your needs. If you plan to play stand-alone games, it is recommended that you consider changing the graphics card. you can choose
How does Java database connection handle transactions and concurrency?
Apr 16, 2024 am 11:42 AM
Transactions ensure database data integrity, including atomicity, consistency, isolation, and durability. JDBC uses the Connection interface to provide transaction control (setAutoCommit, commit, rollback). Concurrency control mechanisms coordinate concurrent operations, using locks or optimistic/pessimistic concurrency control to achieve transaction isolation to prevent data inconsistencies.
Master the power of PHP PDO: advanced queries and updates
Feb 20, 2024 am 08:24 AM
The PHP Data Objects (PDO) extension provides efficient and object-oriented interaction with database servers. Its advanced query and update capabilities enable developers to perform complex database operations, improving performance and code maintainability. This article will delve into the advanced query and update functions of PDO and guide you to master its powerful functions. Advanced queries: Using placeholders and bound parameters Placeholders and bound parameters are important tools for improving query performance and security. Placeholders use question marks (?) to represent replaceable parameters in the query, while bind parameters allow you to specify the data type and value of each parameter. By using these methods, you can avoid SQL injection attacks and improve performance because the database engine can optimize queries ahead of time. //Use placeholder $stmt=$
