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	<title>数据库技术 - 四号程序员</title>
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		<title>Oracle的jdbc使用sid和service_name的区别</title>
		<link>https://www.coder4.com/archives/7753</link>
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		<dc:creator><![CDATA[coder4]]></dc:creator>
		<pubDate>Wed, 06 Jul 2022 04:42:13 +0000</pubDate>
				<category><![CDATA[Linux]]></category>
		<category><![CDATA[数据库技术]]></category>
		<category><![CDATA[Oracle]]></category>
		<category><![CDATA[service_name]]></category>
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					<description><![CDATA[1.使用SERVICE NAME连接： jdbc:oracle:thin:@&#60;host&#62;:&#60;port&#62;/&#60;service name&#62; 如：jdbc:oracle:thin:@//123.123.123.1:8080/SN 注意这里的格式，@后面有//, 以及端口号后的/,不是：（经测试：会报错）。这是与使用SID的主要区别。 这种格式是Oracle 推荐的格式，因为对于集群来说，每个节点的SID 是不一样的，但是SERVICE_NAME 确可以包含所有[......] 继续阅读]]></description>
		
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		<title>Opengauss文档</title>
		<link>https://www.coder4.com/archives/7742</link>
					<comments>https://www.coder4.com/archives/7742#respond</comments>
		
		<dc:creator><![CDATA[coder4]]></dc:creator>
		<pubDate>Wed, 08 Jun 2022 05:34:46 +0000</pubDate>
				<category><![CDATA[数据库技术]]></category>
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					<description><![CDATA[https://opengauss.org/zh/docs/3.0.0/docs/BriefTutorial/BriefTutorial.html[......] 继续阅读]]></description>
		
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		<title>阿里云自建PostgreSQL的性能测试(对比MySQL)</title>
		<link>https://www.coder4.com/archives/7607</link>
					<comments>https://www.coder4.com/archives/7607#respond</comments>
		
		<dc:creator><![CDATA[coder4]]></dc:creator>
		<pubDate>Thu, 16 Dec 2021 09:37:30 +0000</pubDate>
				<category><![CDATA[数据库技术]]></category>
		<category><![CDATA[pg]]></category>
		<category><![CDATA[Postgre]]></category>
		<category><![CDATA[压力测试]]></category>
		<category><![CDATA[压测]]></category>
		<category><![CDATA[性能测试]]></category>
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					<description><![CDATA[1 测试环境 阿里云6代4核8G，PL0磁盘，ecs.g6.xlarge，2台 建议用Ubuntu 20.04，CentOS7的包太老 2 服务器 docker启动pg14 #!/bin/bash NAME="postgres" POSTGRES_USER="pg" POSTGRES_PASS="pg123" VOLUME="$HOME/docker_data/postgres" mkdir -p $VOLUME docker ps -q -a --filte[......] 继续阅读]]></description>
		
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		<title>MySQL 8性能低(于5.7)原因排查</title>
		<link>https://www.coder4.com/archives/7596</link>
					<comments>https://www.coder4.com/archives/7596#respond</comments>
		
		<dc:creator><![CDATA[coder4]]></dc:creator>
		<pubDate>Tue, 14 Dec 2021 09:37:41 +0000</pubDate>
				<category><![CDATA[Linux]]></category>
		<category><![CDATA[数据库技术]]></category>
		<category><![CDATA[5.7]]></category>
		<category><![CDATA[8]]></category>
		<category><![CDATA[MySQL]]></category>
		<category><![CDATA[性能差]]></category>
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					<description><![CDATA[在前文 《阿里云自建MySQL的性能测试(多配置对比)》中，我们发现MySQL 8比MySQL5.7的性能低了33%，今天有空，重新探索了下原因(然而并没有彻底解决）。 1 默认参数差异 根据查阅资料，两者主要有以下默认参数差异： have_query_cache，8中cache被干没了 bin-log，8开启，5.7没开启 innodb_flush_neighbors，8关闭，5.7开启 2 实验1：5.7关闭cache mysql -pmysql123 -e[......] 继续阅读]]></description>
		
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		<title>云数据库ClickHouse二级索引 最佳实践</title>
		<link>https://www.coder4.com/archives/7266</link>
					<comments>https://www.coder4.com/archives/7266#respond</comments>
		
		<dc:creator><![CDATA[coder4]]></dc:creator>
		<pubDate>Wed, 23 Jun 2021 08:05:08 +0000</pubDate>
				<category><![CDATA[数据库技术]]></category>
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					<description><![CDATA[转载自：https://developer.aliyun.com/article/781180?spm=a2c6h.12873581.0.dArticle781180.58d5802f7iyZ39[......] 继续阅读]]></description>
		
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		<title>MySQL添加唯一索引前去除重复数据</title>
		<link>https://www.coder4.com/archives/7025</link>
					<comments>https://www.coder4.com/archives/7025#respond</comments>
		
		<dc:creator><![CDATA[coder4]]></dc:creator>
		<pubDate>Wed, 03 Jun 2020 22:18:15 +0000</pubDate>
				<category><![CDATA[数据库技术]]></category>
		<category><![CDATA[MySQL]]></category>
		<category><![CDATA[去重]]></category>
		<category><![CDATA[唯一索引]]></category>
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					<description><![CDATA[delete from YOUR_TABLE where id not in (select id from (select max(id) as id from YOUR_TABLE group by UNIQUE_FIELD) as b); &#160;[......] 继续阅读]]></description>
		
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		<title>MySQL事务＆并发实际操合集</title>
		<link>https://www.coder4.com/archives/6209</link>
					<comments>https://www.coder4.com/archives/6209#respond</comments>
		
		<dc:creator><![CDATA[coder4]]></dc:creator>
		<pubDate>Tue, 09 Oct 2018 02:20:06 +0000</pubDate>
				<category><![CDATA[数据库技术]]></category>
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					<description><![CDATA[1. "UPDATE tbl SET count = count - 10 WHERE id = 1"这种SQL能否保证并发事务安全。 答：可以，UPDATE操作会针对id加锁，且"x = x - y"会再最新提交的结果上计算。 演示： t1 set autocommit = 0; begin; update clockin_test set count = count - 10; t2 set autocommit = 0; begin; update cl[......] 继续阅读]]></description>
		
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		<title>如何将utf8的表转为utf8mb4</title>
		<link>https://www.coder4.com/archives/6091</link>
					<comments>https://www.coder4.com/archives/6091#respond</comments>
		
		<dc:creator><![CDATA[coder4]]></dc:creator>
		<pubDate>Thu, 05 Jul 2018 02:29:09 +0000</pubDate>
				<category><![CDATA[数据库技术]]></category>
		<category><![CDATA[MySQL]]></category>
		<category><![CDATA[utf8mb4]]></category>
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					<description><![CDATA[ALTER TABLE xxx CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci; &#160;[......] 继续阅读]]></description>
		
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		<title>理解MySQL的四种事务隔离级别</title>
		<link>https://www.coder4.com/archives/5996</link>
					<comments>https://www.coder4.com/archives/5996#respond</comments>
		
		<dc:creator><![CDATA[coder4]]></dc:creator>
		<pubDate>Sun, 25 Mar 2018 08:37:17 +0000</pubDate>
				<category><![CDATA[数据库技术]]></category>
		<category><![CDATA[MySQL]]></category>
		<category><![CDATA[事物隔离级别]]></category>
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					<description><![CDATA[转载自：《MySQL的四种事务隔离级别》 一、事务的基本要素（ACID） 原子性（Atomicity）：事务开始后所有操作，要么全部做完，要么全部不做，不可能停滞在中间环节。事务执行过程中出错，会回滚到事务开始前的状态，所有的操作就像没有发生一样。也就是说事务是一个不可分割的整体，就像化学中学过的原子，是物质构成的基本单位。 一致性（Consistency）：事务开始前和结束后，数据库的完整性约束没有被破坏 。比如A向B转账，不可能A扣了钱，B却没收到。 隔离性（Is[......] 继续阅读]]></description>
		
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		<title>[转]MySQL中的SELECT FOR UPDATE</title>
		<link>https://www.coder4.com/archives/5625</link>
					<comments>https://www.coder4.com/archives/5625#respond</comments>
		
		<dc:creator><![CDATA[coder4]]></dc:creator>
		<pubDate>Wed, 26 Jul 2017 08:14:02 +0000</pubDate>
				<category><![CDATA[数据库技术]]></category>
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					<description><![CDATA[转载自：http://www.cnblogs.com/chenwenbiao/archive/2012/06/06/2537508.html MySQL  使用SELECT ... FOR UPDATE 做事务写入前的确认 以MySQL 的InnoDB 为例，预设的Tansaction isolation level 为REPEATABLE READ，在SELECT 的读取锁定主要分为两种方式: SELECT ... LOCK IN SHARE MODE SELECT .[......] 继续阅读]]></description>
		
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