非空字段空值对查询的影响
BLOG有三年没有更新了，其实这篇文档也是三年前写的，不过当时没有贴出来，今天看到有人问起，于是分享出来。 这是客户数据库中碰到的一个有意思的问题。 数据库版本为11.2.0.3，客户的DSG同步软件在同步某张表时出现了错误，报错无非插入空值ORA-1400，本来这是一个很简单的问题，但是诊断发现问题比较有意思： SQL> select * from t_def; ID NAME TYPE...
View Article非空字段空值的产生
上一篇讨论了非空字段中如果存在空值对于查询的影响，这里描述一下导致问题的原因。 非空字段空值对查询的影响：http://yangtingkun.net/?p=1481 书接上文，其实CBO的判断本身是没有问题的，问题在于，为什么一个空值会存在非空约束的字段中。 重新看一下问题： SQL> select * from t_def; ID NAME TYPE ----------...
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MySQL DATETIME VS TIMESTAMP
A question which would come sometimes to mind when starting with MySQL is whether I should use DATETIME or TIMESTAMP data type since both appear to store same date and time component. Similarities...
View Article12c的GI下cvu目录满
12c的GI中，/oracle_grid/app/oracle/crsdata/@global/cvu/baseline/cvures这个目录下的文件占用空间巨大。某生产环境中，目录已经到了32G以上。 这可能和如下3个bug有关： Unpublished Bug 18143707 CVU NEED TO DO CVU BASELINE REPORT CLEAN TO AVOID DISK FULL...
View ArticleMyRocks has some strange performance issues for index scans
The details on this issue are here:https://github.com/facebook/mysql-5.6/issues/369 This test is very simple. I loaded the SSB (star schema benchmark) data for scale factor 20 (12GB raw data), added...
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CVE-2016-6225: Percona Xtrabackup Encryption IV Not Being Set Properly
If you are using Percona XtraBackup with xbcrypt to create encrypted backups, and are using versions older than 2.3.6 or 2.4.5, we advise that you upgrade Percona XtraBackup. Note: this does not...
View ArticleWhen order of appearance of indexes matters in MySQL
Sometimes MySQL surprises you in ways you would have never imagined. Would you think that the order in which the indexes appear in a table matters?It does. Mind you, not the order of the columns – the...
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SET PASSWORD will lock you out of your slave in a mixed 5.6/5.7 MySQL topology
Long time no post…. Here’s something interesting. Last week I decided to give MySQL 5.7 a try (yes, I am kinda conservative DBA…) and the very same day that I installed my first 5.7 replica I noticed...
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Does the Meltdown Fix Affect Performance for MySQL on Bare Metal?
In this blog post, we’ll look at does the Meltdown fix affect performance for MySQL on bare metal servers. Since the news about the Meltdown bug, there were a lot of reports on the performance hit...
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MyRocks Disk Full Edge Case
RocksDB engine—and it’s MySQL implementation MyRocks—is a very good alternative engine for MySQL. It has proven to be very efficient and stable for many workloads, including those of large scale....
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