blocks|key|1861606|text|将逻辑放在数据库中，这些语义基本上已经为您解决了。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1861607|update+teams
set+score+=+score+%2B+1
where+team_id+=+1|code-block|syntax|javascript|1861608|。。或者其他比分和队号。|1861609|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Keep the logic at the DB, those semantics have mostly been solved for you.

<pre><code>update teams
set score = score + 1
where team_id = 1
</code></pre>

.. or whatever score and whatever team number.

blocks|key|493710|text|数据库管理并发锁定，并确保更改是自动进行的。这是使用支持ACID事务的数据库的好处。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|493711|在大多数情况下，更改足够快，因此锁争用非常小。但是它仍然可能发生，所以您需要检查在执行SQL查询后返回的错误状态。如果出现问题，mysql_query()函数将返回FALSE。|style|CODE|493712|然后找出原因(更新冲突、权限不足、SQL语法错误等)通过调用mysql_errno()。有关MySQL错误代码参考，请参阅http://dev.mysql.com/doc/refman/5.1/en/error-messages-server.html。|493713|entityMap|0|LINK|mutability|MUTABLE|url|http://en.wikipedia.org/wiki/ACID|1|http://dev.mysql.com/doc/refman/5.1/en/error-messages-server.html^0|S|4|0|0|1S|D|2A|5|0|U|D|1P|1T|1|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@$A|U|B|V|1|W]]|C|$]]|$1|D|3|E|5|6|7|X|8|@$A|Y|B|Z|F|G]|$A|10|B|11|F|G]]|9|@]|C|$]]|$1|H|3|I|5|6|7|12|8|@$A|13|B|14|F|G]]|9|@$A|15|B|16|1|17]]|C|$]]|$1|J|3|-4|5|6|7|18|8|@]|9|@]|C|$]]]|K|$L|$5|M|N|O|C|$P|Q]]|R|$5|M|N|O|C|$P|S]]]]

The database manages concurrent locking and ensures that changes are made atomically. This is a benefit of using a database that supports <a href="http://en.wikipedia.org/wiki/ACID" rel="nofollow noreferrer">ACID</a> transactions. 

In most cases changes are quick enough that lock contention is minimal. But it can still happen, so you need to check for error status returned after you execute an SQL query. The <code>mysql_query()</code> function returns <code>FALSE</code> if there's a problem. 

Then you get to figure out the cause (update conflict, insufficient permissions, SQL syntax error, etc.) by calling <code>mysql_errno()</code>. See <a href="http://dev.mysql.com/doc/refman/5.1/en/error-messages-server.html" rel="nofollow noreferrer">http://dev.mysql.com/doc/refman/5.1/en/error-messages-server.html</a> for MySQL error code reference.

blocks|key|493728|text|如果您的实际问题比这个简单的示例更大，那么您应该结合使用事务和锁表，以确保用户不会互相覆盖。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|493729|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

IF your real world problem is bigger than this simple example, you should use a transaction in conjunction with lock tables to make sure users don't overwrite each other.

blocks|key|1793304|text|我同意Xepochs的回答，除非你绝对需要，否则不要引入并发问题。有关不同锁定策略的很好答案，请参阅here。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1793305|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/129329/optimistic-vs-pessimistic-locking/129397#129397^0|1E|4|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

I agree with Xepochs answer, don't introduce concurrency concerns unless you absolutely need to. For a great answer regarding different locking strategies see <a href="https://stackoverflow.com/questions/129329/optimistic-vs-pessimistic-locking/129397#129397">here</a>.

blocks|key|1861760|text|主要数据库就是为处理这种情况而设计的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1861761|在使用MySQL时，InnoDB存储引擎具有行锁定功能，该功能可锁定正在写入的行。因此，任何针对同一行的update请求都将等待，直到该行上的上一个操作完成。|1861762|如果使用MyISAM存储引擎，则在更新行时会锁定整个表。当多个玩家同时推送更新请求时，这会在服务器上造成阻塞。因此，这一切都是关于什么数据库，特别是什么存储引擎，您正在使用的目的。|1861763|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

Major databases are designed to handle such situations.

When using MySQL, the InnoDB storage engine has the row-locking feature, which locks the row that is being written to. So, any update request that is for the same row will wait until the previous operation on the row completes.

If you use MyISAM storage engine, that locks the whole table when a row is being updated. That creates a choke on the server when multiple players simultaneously push update requests. So it is all about what database and particularly what storage engine you are using for the purpose.

blocks|key|455041|text|我不敢相信上面的答案都不能说明你可能遇到了设计缺陷。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|455042|是的，所有的答案都是正确的，mysql可以处理竞速条件和表的互斥访问。|455043|然而，如果你遇到这样的问题，可能是时候重新考虑你的设计了。为什么你不为那些增加了一部分奖金的人保留一个用户id？然后，您可以拥有一个：|455044|++++INSERT+INTO+team1(userid,+amount)+VALUES(32,+100);
++++SELECT+SUM(amount)+FROM+team1
or
++++REPLACE+INTO+team1+SET+amount+=+$total|code-block|syntax|javascript|455045|但如果是我的话我甚至不会费心。我会简单地使用set_cookie(team_score，team_score%2Bamount)并保留客户端的所有内容。当我想要读取比分时，我会触发一个AJAX请求来读取或写入服务器，同时仍然异步地更新客户端接口。既然您指出您的web开发是基本的，我建议您研究一下用于异步客户端-服务器通信的jQuery框架，因为它是实现这一点的最简单的方法。|455046|EDIT:，对于当其他玩家添加分数时更新每个人的UI的问题，我建议您查看backbone.js，它将您的数据模型很好地绑定到玩家的客户端，以便他们在分数变化时立即获得更新。|offset|length|style|BOLD|455047|entityMap^0|0|0|0|0|0|0|5|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|W|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|X|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|6|7|Y|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|Z|8|@$O|10|P|11|Q|R]]|9|@]|A|$]]|$1|S|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|T|$]]

I can't believe that none of the above answers are pointing out that you may be running into a design flaw.

Yes all the answers are correct, mysql can handle racing conditions and mutually exclusive access to tables. 

However, if you come across a problem like this it is probably time to re-think your design. Why are you not keeping a user id for whoever added a portion of their winnings? You could then have a:

<pre><code> INSERT INTO team1(userid, amount) VALUES(32, 100);
 SELECT SUM(amount) FROM team1
or
 REPLACE INTO team1 SET amount = $total
</code></pre>

But if it was me, I wouldn't even bother. I would simply set_cookie(team_score, team_score+amount) and keep everything client side. When I would want to read the score I would fire an AJAX request to read or write to the server and still update the client interface asynchronously. Since you point out that your web development is basic I recommend that you have a look at the jQuery framework for asynchronous client-server communication as it is by far the easiest way to achieve this.

EDIT: And for the problem of updating everyone's UI when another player adds an amount to the score, I suggest you look into backbone.js which tights your data model nicely to the players' client so that they get immediate updates when the score changes.

blocks|key|1795093|text|数据库具有内置的并发控制，例如，您可以阅读postgres并发控制here。如果我是对的，pgsql的默认设置是乐观锁定和读提交事务隔离，这意味着每个事务都知道其他未提交事务所做的更改。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1795094|在您的情况下，这些设置是可以的，所以您可以简单地执行UPDATE+team1+SET+score+=+score+%2B+mytotal，数据库将很好地处理并发问题。|style|CODE|1795095|如果您有较长的select+-+update问题，那么可以使用SELECT+FOR+UPDATE查询通过第一次select手动锁定行。|1795096|这些是目前的最佳实践...|1795097|entityMap|0|LINK|mutability|MUTABLE|url|http://www.postgresql.org/docs/9.3/static/mvcc.html^0|X|4|0|0|Q|14|0|V|H|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@$A|U|B|V|1|W]]|C|$]]|$1|D|3|E|5|6|7|X|8|@$A|Y|B|Z|F|G]]|9|@]|C|$]]|$1|H|3|I|5|6|7|10|8|@$A|11|B|12|F|G]]|9|@]|C|$]]|$1|J|3|K|5|6|7|13|8|@]|9|@]|C|$]]|$1|L|3|-4|5|6|7|14|8|@]|9|@]|C|$]]]|M|$N|$5|O|P|Q|C|$R|S]]]]

Databases have built in concurrency control, for example you can read about postgres concurrency control <a href="http://www.postgresql.org/docs/9.3/static/mvcc.html" rel="nofollow">here</a>. If I am right, the default settings by pgsql are optimistic locking and read committed transaction isolation, which means that every transaction is aware of the changes done by other uncommitted transactions.

In you case these settings are okay, so you can do simply <code>UPDATE team1 SET score = score + mytotal</code>, and the database will handle well the concurrency issues.

If you have a longer select - update issue, then you can lock the rows manually by the first select with a <code>SELECT FOR UPDATE</code> query.

These are the best practices currently...

I've been doing some web development work in PHP recently which has led me to study up on the language in general. So far I have not needed to use it to interact with a database, but I know it provides a lot of convenient functions for doing so.

Although I know basic SQL and have worked with basic manipulation of data in a database, I don't understand how web developers who base their websites around PHP/Javascript/SQL are able to manage users modifying the same data at the same time.

For example, lets say you have a blackjack website which divides users into one of two teams when they sign up. Every time a user wins a game, a portion of their winnings is added to a running total for that team.

So lets say the pseudo code for the function that does this looks something like this:

<pre><code>... 
$total = mysql_query("SELECT score FROM team1");
$total = $total + $mytotal;
mysql_query("UPDATE team1 SET score='".$total."'");
...
</code></pre>

If two players are playing at the same time, it's very possible that they will both call SELECT before the other one has a chance to increment and update the table, so one users changes will be immediately overwritten. 

My question is, how does one avoid this? Is it done using PHP at the code level, or are there features provided by whatever database you are using that help to prevent this? 

I've been doing some research, and it seems that PHP does provide a <a href="http://us.php.net/sem" rel="noreferrer">semaphore</a> mechanism, and I've also noticed that mysql offers a <a href="http://dev.mysql.com/doc/refman/5.0/en/lock-tables.html" rel="noreferrer">LOCK table feature</a>. However, I'm not sure which of these, if either, is used in practice.

PHP and Concurrency

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我最近一直在做一些PHP的web开发工作，这让我开始学习这门语言。到目前为止，我还不需要使用它来与数据库交互，但我知道它提供了许多方便的函数来这样做。虽然我知道基本的SQL，并使用过数据库中数据的基本操作，但我不明白基于PHP/Javascript/SQL的网站开发人员如何能够管理同时修改相同数据的用户。例如，假设你有...

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