OracleBlog – 第 3 页 – 笑看数据库江湖的那些事儿……

MySQL waiting for metadata lock的分析

2019-09-03 没有评论

处理waiting for metadata lock，需要: 1. 平时打开performance_schema(以下简称PS)的instruments。 2. 查询PS.metadata_locks ，找到状态为PENDING的thread。 3. 查询PS.threads,关联PS.metad […]

..experience, Working case

数据库序列的监控

2019-08-03 没有评论

需要监控数据库的序列，在达到最大值前，进行告警。特别是mysql，往往因为字段的定义和auto incremental的定义不同，导致各自的上限不同。 Oracle：

SELECT 
x.*,
CASE WHEN increment_by<0
 THEN round(last_number/min_value*100,4)
WHEN increment_by>0
  THEN round(last_number/max_value*100,4)
 ELSE 0
  END 
AS percent_usage
from DBA_SEQUENCES x  WHERE cycle_flag='N'
ORDER BY percent_usage DESC;

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SELECT

x.*,

CASE WHEN increment_by<0

THEN round(last_number/min_value*100,4)

WHEN increment_by>0

THEN round(last_number/max_value*100,4)

ELSE 0

END

AS percent_usage

from DBA_SEQUENCES x WHERE cycle_flag='N'

ORDER BY percent_usage DESC;

SQL Server: [crayon-63d49ce693150 […]

..experience, Working case

隐式转换检查

2019-08-03 没有评论

数据库中是隐式转换往往是性能的杀手，下面2个语句分别可以在sql server和oracle查询到目前在内存中的，使用了隐式转换的SQL： sql server 隐式转换：

DECLARE @dbname SYSNAME  
SET @dbname = QUOTENAME(DB_NAME());  
WITH XMLNAMESPACES(DEFAULT 'http://schemas.microsoft.com/sqlserver/2004/07/showplan')  
SELECT stmt.value('(@StatementText)[1]', 'varchar(max)') AS SQL_Text ,  
         t.value('(ScalarOperator/Identifier/ColumnReference/@Schema)[1]', 'varchar(128)') AS SchemaName ,  
         t.value('(ScalarOperator/Identifier/ColumnReference/@Table)[1]', 'varchar(128)') AS TableName ,  
         t.value('(ScalarOperator/Identifier/ColumnReference/@Column)[1]', 'varchar(128)') AS ColumnName ,  
         ic.DATA_TYPE AS ConvertFrom ,  
         ic.CHARACTER_MAXIMUM_LENGTH AS ConvertFromLength ,  
         t.value('(@DataType)[1]', 'varchar(128)') AS ConvertTo ,  
         t.value('(@Length)[1]', 'int') AS ConvertToLength ,  
         query_plan  
FROM sys.dm_exec_cached_plans AS cp  
--FROM sys.dm_exec_query_stats qs
CROSS APPLY sys.dm_exec_query_plan(plan_handle) AS qp  
CROSS APPLY query_plan.nodes('/ShowPlanXML/BatchSequence/Batch/Statements/StmtSimple')AS batch ( stmt )  
CROSS APPLY stmt.nodes('.//Convert[@Implicit="1"]') AS n ( t )  
JOIN INFORMATION_SCHEMA.COLUMNS AS ic ON QUOTENAME(ic.TABLE_SCHEMA) = t.value('(ScalarOperator/Identifier/ColumnReference/@Schema)[1]', 'varchar(128)')  
    AND QUOTENAME(ic.TABLE_NAME) = t.value('(ScalarOperator/Identifier/ColumnReference/@Table)[1]','varchar(128)')  
    AND ic.COLUMN_NAME = t.value('(ScalarOperator/Identifier/ColumnReference/@Column)[1]','varchar(128)')  
WHERE t.exist('ScalarOperator/Identifier/ColumnReference[@Database=sql:variable("@dbname")][@Schema!="[sys]"]') = 1 
and ic.DATA_TYPE != t.value('(@DataType)[1]', 'varchar(128)')

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DECLARE @dbname SYSNAME

SET @dbname = QUOTENAME(DB_NAME());

WITH XMLNAMESPACES(DEFAULT 'http://schemas.microsoft.com/sqlserver/2004/07/showplan')

SELECT stmt.value('(@StatementText)[1]', 'varchar(max)') AS SQL_Text ,

t.value('(ScalarOperator/Identifier/ColumnReference/@Schema)[1]', 'varchar(128)') AS SchemaName ,

t.value('(ScalarOperator/Identifier/ColumnReference/@Table)[1]', 'varchar(128)') AS TableName ,

t.value('(ScalarOperator/Identifier/ColumnReference/@Column)[1]', 'varchar(128)') AS ColumnName ,

ic.DATA_TYPE AS ConvertFrom ,

ic.CHARACTER_MAXIMUM_LENGTH AS ConvertFromLength ,

t.value('(@DataType)[1]', 'varchar(128)') AS ConvertTo ,

t.value('(@Length)[1]', 'int') AS ConvertToLength ,

query_plan

FROM sys.dm_exec_cached_plans AS cp

--FROM sys.dm_exec_query_stats qs

CROSS APPLY sys.dm_exec_query_plan(plan_handle) AS qp

CROSS APPLY query_plan.nodes('/ShowPlanXML/BatchSequence/Batch/Statements/StmtSimple')AS batch ( stmt )

CROSS APPLY stmt.nodes('.//Convert[@Implicit="1"]') AS n ( t )

JOIN INFORMATION_SCHEMA.COLUMNS AS ic ON QUOTENAME(ic.TABLE_SCHEMA) = t.value('(ScalarOperator/Identifier/ColumnReference/@Schema)[1]', 'varchar(128)')

AND QUOTENAME(ic.TABLE_NAME) = t.value('(ScalarOperator/Identifier/ColumnReference/@Table)[1]','varchar(128)')

AND ic.COLUMN_NAME = t.value('(ScalarOperator/Identifier/ColumnReference/@Column)[1]','varchar(128)')

WHERE t.exist('ScalarOperator/Identifier/ColumnReference[@Database=sql:variable("@dbname")][@Schema!="[sys]"]') = 1

and ic.DATA_TYPE != t.value('(@DataType)[1]', 'varchar(128)')

oracle隐式转换： [crayon-63d49ce693 […]

Study note

小记scn head room

2019-08-03 没有评论

小记一下前段时间看的scn head room的问题。 1. scn的最大值。scn的表示是SCN_WRAP.SCN_BASE，最大值是 ffff.ffffffff，即65535.4294967295，也就是每当scn_base到ffffffff（或者说4294967295）的时候，scn wrap […]

Study note

在Docker上安装oracle 19c

2019-02-16 5条评论

基于docker的安装非常简单。其实就两行核心命令：

./buildDockerImage.sh -v 19.2.0 -e
docker run --name oracle19c -p 1521:1521 -p 5500:5500 -v /Users/lovehouse/iDocker/dockervolums/oradata/oracle19c:/opt/oracle/oradata oracle/database:19.2.0-ee

1 2	./buildDockerImage.sh -v 19.2.0 -e docker run --name oracle19c -p 1521:1521 -p 5500:5500 -v /Users/lovehouse/iDocker/dockervolums/oradata/oracle19c:/opt/oracle/oradata oracle/database:19.2.0-ee

我们假设你已经在Mac上安装好了docker，我们开始安装oracle 19c。在docker上安装数据库或应用，是基于dockerfile的，目前Oracle官方还没发布基于1 […]

..experience, Working case

aws RDS 版本升级最佳实践的探讨

2019-02-03 一条评论

这篇文章其实在草稿箱中存在了挺长的一段时间，去年10月就已经开始写了，但是由于工作上的其他事情的干扰，一直还没写完。所以你可以看到我画的图中，now其实是指2018年10月（OCT）。趁着过年休假，把这个文章终于写完了。 aws rds被强制升级是个无奈的事情，版本不支持，而被强制升级会影响业务可用 […]

..experience, Working case

SQL Server报错The datediff function resulted in an overflow

2018-12-26 没有评论

zabbix的监控有一个报错:

The datediff function resulted in an overflow. The number of dateparts separating two date/time instances is too large. Try to use datediff with a less precise datepart.

1	The datediff function resulted in an overflow. The number of dateparts separating two date/time instances is too large. Try to use datediff with a less precise datepart.

经检查，这个报错，调用的是下面的一个监控：

select count(*) as cnt from sys.sysprocesses 
where  DateDiff(ss,last_batch,getDate())>=10 
and lastwaittype Like 'PAGE%LATCH_%' 
And waitresource Like '2:%'

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select count(*) as cnt from sys.sysprocesses

where DateDiff(ss,last_batch,getDate())>=10

and lastwaittype Like 'PAGE%LATCH_%'

And waitresource Like '2:%'

这个监控脚本，是用来监控发生在temp上的pagelatch_up的争用。监控脚本中，包含了 […]

..experience, Working case

MySQL 不显示输出结果

2018-12-12 没有评论

有的时候，想看看语句执行时间有多长，但是有不想看的刷屏的输出，各个数据库可以用下面的方法：（1）Oracle： set autotrace trace，恢复的话，用set autottrace off （2）postgresql： EXPLAIN ANALYZE （3）MySQL： pager c […]

..experience, Working case

Azure云MySQL数据库受限功能列表

2018-11-20 没有评论

微软Azure云MySQL功能受限列表（截止2018年4月）多样性支持的数据库种类 SQL Server MySQL、MariaDB Postgresql CosmosDB（类似MongoDB） Redis 高可用性支持的区域 Azure中国账号支持2个区域 Azure全球账号支 […]

Study note

raft协议学习笔记

2018-11-18 没有评论

注，需要注意的是raft是个默认消息可靠，但是不提防消息有害的系统。（一）. 共识机制有2种：一种是leader-less（对称的），即没有leader，大家都是平等的，客户端可以连接任意的节点。一种是leader-base（非对称的），即有leader，在任意的某个时间点，只有一个leade […]

..experience, Working case

centos 7中配置keepalived日志为别的路径

2018-10-18 没有评论

keepalived 安装：

cd <keepalived_sourcecode_path>
./configure --prefix=/usr/local/keepalived

make &&  make install

mkdir /etc/keepalived
mkdir /etc/keepalived/scripts
cp /usr/local/keepalived/etc/keepalived/keepalived.conf /etc/keepalived/
cp /root/keepalived-2.0.6/keepalived/etc/init.d/keepalived  /etc/init.d/
cp /usr/local/keepalived/sbin/keepalived /sbin/keepalived
cp /usr/local/keepalived/etc/sysconfig/keepalived /etc/sysconfig/
chmod +x /etc/init.d/keepalived

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cd <keepalived_sourcecode_path>

./configure --prefix=/usr/local/keepalived

make && make install

mkdir /etc/keepalived

mkdir /etc/keepalived/scripts

cp /usr/local/keepalived/etc/keepalived/keepalived.conf /etc/keepalived/

cp /root/keepalived-2.0.6/keepalived/etc/init.d/keepalived /etc/init.d/

cp /usr/local/keepalived/sbin/keepalived /sbin/keepalived

cp /usr/local/keepalived/etc/sysconfig/keepalived /etc/sysconfig/

chmod +x /etc/init.d/keepalived

由于在默认状态下keepalived的日志会写入到/var/log/message中，我们需要将此剥离出来。在centos 6下可以：

（1）首先修改/etc/sysconfig/keepalived文件，注释掉如下，添加如下： 
#KEEPALIVED_OPTIONS="-D"
KEEPALIVED_OPTIONS="-D -d -S 0" 

（2）其次修改 /etc/rsyslog.conf 文件，添加如下：
local0.* /var/log/keepalived.log

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（1）首先修改/etc/sysconfig/keepalived文件，注释掉如下，添加如下：

#KEEPALIVED_OPTIONS="-D"

KEEPALIVED_OPTIONS="-D -d -S 0"

（2）其次修改 /etc/rsyslog.conf 文件，添加如下：

local0.* /var/log/keepalived.log

[…]

Study note

18c新特性的一些小结

2018-02-20 一条评论

Oracle 18c在2018-02-16 release出来的，还是秉承着Oracle的cloud first理念，18c现在cloud和Engineered Systems上推出，想在传统的机器上安装18c，估计还要等到2018年下半年。下面，我从我的角度，来快速review一下值得关注的18 […]