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alexcai — Fri, 10 Nov 2017 07:25:00 GMT

已经一个多月没有写东西了，不过最�q�确实很忙。前两天在线上碰��C��个C3P0的链接死锁的异常�Q�话说这个上古神�?,我已�l�是很久不碰了。先贴异�?/p>

异常截图

"apparent deadlocks"�Q�名词解释是说c3p0拿到链接之后�Q�最�l��用之后没有返回到pool,��D��死链��失败。经�q�在stack Overflow��?https://stackoverflow.com/questions/3730844/c3p0-apparent-deadlock-when-the-threads-are-all-empty.发现增加一个statementCacheNumDeferredCloseThreads该参数的定义�Q�就可以避免�q�个问题�?/p>

�l�过查看官方文档�Q�http://www.mchange.com/projects/c3p0/#statementCacheNumDeferredCloseThreads

解释�Q�如果把该��D��q?�Q�statement的缓存就会自动跟�t�当前可用的connections,如果没有再用�Q�就会自动销毁掉。如果需要另外的�U�程来专门销毁缓存的statement,则还需要设�|�maxStatements与maxStatementsPerConnection�?/p>

再脓一个官方的说明�Q?/p>

Configuring Statement Pooling

c3p0 implements transparent PreparedStatement pooling as defined by the JDBC spec. Under some circumstances, statement pooling can dramatically improve application performance. Under other circumstances, the overhead of statement pooling can slightly harm performance. Whether and how much statement pooling will help depends on how much parsing, planning, and optimizing of queries your databases does when the statements are prepared. Databases (and JDBC drivers) vary widely in this respect. It's a good idea to benchmark your application with and without statement pooling to see if and how much it helps.

You configure statement pooling in c3p0 via the following configuration parameters:

maxStatements

maxStatementsPerConnection

statementCacheNumDeferredCloseThreads

maxStatementsis JDBC's standard parameter for controlling statement pooling.maxStatementsdefines the total numberPreparedStatementsa DataSource will cache. The pool will destroy the least-recently-used PreparedStatement when it hits this limit. This sounds simple, but it's actually a strange approach, because cached statements conceptually belong to individual Connections; they are not global resources. To figure out a size formaxStatementsthat does not "churn" cached statements, you need to consider the number offrequently usedPreparedStatements in your application,and multiply that by the number of Connections you expect in the pool (maxPoolSizein a busy application).

maxStatementsPerConnectionis a non-standard configuration parameter that makes a bit more sense conceptually. It defines how many statements each pooled Connection is allowed to own. You can set this to a bit more than the number ofPreparedStatementsyour applicationfrequentlyuses, to avoid churning.

If either of these parameters are greater than zero, statement pooling will be enabled. If both parameters are greater than zero, both limits will be enforced. If only one is greater than zero, statement pooling will be enabled, but only one limit will be enforced.

大概意思就是这两个�Q�有一个值如果大�?�Q�c3p0的statement pool��׃��发生作用�?/p>

以上所有的配置都是��Z��c3p0的最新版本。PS一下，�q�是2015�q�的JAR�?/p>

通过引入最新的C3P0包，另外增加了两�D�配�|�，�U�上观察两天�Q�问题解冟�?/p>

最后打个小�q�告�Q�JAVA世界最快的JDBC�q�接池，�?a target="_blank" style="color: #3194d0; text-decoration-line: none;">HikariCP莫属。已�l�甩c3p0好几个街角，有图有真像�?/p>

alexcai 2017-11-10 15:25 发表评论

关于word在表格拆分与�l�合那些事儿

alexcai — Fri, 25 Aug 2017 07:54:00 GMT

摘要: 在word的处理之中，文字�Q�各�U�类型的囄��Q�最复杂的公式，之前�~�写的API基本都覆盖了。不�q�，昨天在做一个文档测试时�Q�发现表格没有能很好的处理�?nbsp; 阅读全文

alexcai 2017-08-25 15:54 发表评论

hadoop之分布式文�g存储hdfs

alexcai — Mon, 24 Jul 2017 02:35:00 GMT

摘要: HDFS和MapReduce是Hadoop的两大核心，除此之外Hbase、Hive�q�两个核心工具也随着Hadoop发展变得��来��重要。今天我们只初步的看看HDFS. 阅读全文

alexcai 2017-07-24 10:35 发表评论

打造基于thrift的RPC服务

alexcai — Thu, 29 Jun 2017 08:39:00 GMT

摘要: 使用thrift已经有段旉��了，目前基本是clien+server的方式，负蝲是通过nginx来处理。这�U�处理方式有两个比较大的弊端�Q?nbsp; 阅读全文

alexcai 2017-06-29 16:39 发表评论

markdown to doc,doc to markdown(��q��入繁�Q�花�J��ؓ��)

alexcai — Fri, 02 Jun 2017 01:45:00 GMT

www.taggerin.com�Q�主要处理日常文档的在线�~�辑�Q�以及与Markdown,PDF,html�{�格式的双向转换.听说内测版本已经发布。真正的文档在线�~�辑与预览。

alexcai 2017-06-02 09:45 发表评论

alexcai — Thu, 15 Dec 2016 05:33:00 GMT

摘要: 一般的业务开发，不会涉及到多�U�数据库�c�d��的操作。因为，无论是对于开发，�q�是�q�维�Q�成本都是非帔R��的。如果是ORACLE数据库到MYSQL的数据备份，目前我所了解的开源解��x��案有2�U�：阅读全文

alexcai 2016-12-15 13:33 发表评论

话说微信支付接入

alexcai — Tue, 26 Jul 2016 03:59:00 GMT

摘要: 作�ؓ日常支付业务�Q�微信的接入逐渐�q�入了大家的视野。今天以PC端接入微信支付的基本��程来说明�?nbsp; 阅读全文

alexcai 2016-07-26 11:59 发表评论

Word处理主题--在网��上昄��公式

alexcai — Fri, 15 Jul 2016 00:30:00 GMT

摘要: 在WORD里面�~�辑公式�Q�目前是有两�U�方法�?nbsp; 阅读全文

alexcai 2016-07-15 08:30 发表评论

Tomcat的性能提升之apr

alexcai — Fri, 08 Jul 2016 01:50:00 GMT

摘要: 最�q�在弄项目的压测�Q�首先想到把应用服务器TOMCAT的相关配�|�升�U�，�|�上看了很多关于TOMCAT升��的案例，于是�l�合自己的实际情况，做了�W�记�?nbsp; 阅读全文

alexcai 2016-07-08 09:50 发表评论

alexcai — Wed, 29 Jun 2016 10:14:00 GMT

摘要: 当我们��E到RPC服务框架�Q�放��g��界范��_��我目前知道的��L��有thrift,fingle,grpc�{�。当然大型互联网公司都会有自��q��RPC服务与治理框架。经�q�一�D�|��间的调研�Q�本着��单，高效的原�?最�l�选择thrift.具体原因�Q�等接下来写到服务篇的时候再�l�说�?nbsp; 阅读全文

alexcai 2016-06-29 18:14 发表评论