Study note

读书笔记-《Best Practices for Gathering Optimizer Statistics with Oracle Database 19c》

2024-05-14 没有评论

调整SET_TABLE_PREFS，按照表来单独设置，减低stale的百分比，比如变化1%就收集统计信息调整 ESTIMATE_PERCENT的比例，不用AUTO_SAMPLE_SIZE，而用更低的采样比例 High-frequency Optimizer Statistics Collectio […]

Study note

数据库内查询pg的表结构定义

2020-09-24 没有评论

需要利用到plperlu和自己写一个system函数。

-bash-4.2$ psql
psql (9.6.2)
Type "help" for help.

postgres=# create extension plperlu;
CREATE EXTENSION
postgres=# \dx
                      List of installed extensions
  Name   | Version |   Schema   |              Description               
---------+---------+------------+----------------------------------------
 plperlu | 1.0     | pg_catalog | PL/PerlU untrusted procedural language
 plpgsql | 1.0     | pg_catalog | PL/pgSQL procedural language
(2 rows)

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-bash-4.2$ psql

psql (9.6.2)

Type "help" for help.

postgres=# create extension plperlu;

CREATE EXTENSION

postgres=# \dx

List of installed extensions

Name | Version | Schema | Description

---------+---------+------------+----------------------------------------

plperlu | 1.0 | pg_catalog | PL/PerlU untrusted procedural language

plpgsql | 1.0 | pg_catalog | PL/pgSQL procedural language

(2 rows)

postgres=# CREATE OR REPLACE FUNCTION system(text) RETURNS text
postgres-# AS 'my $cmd=shift; return `cd /tmp;$cmd`;' LANGUAGE plperlu;
CREATE FUNCTION
postgres=# 
postgres=#

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postgres=# CREATE OR REPLACE FUNCTION system(text) RETURNS text

postgres-# AS 'my $cmd=shift; return `cd /tmp;$cmd`;' LANGUAGE plperlu;

CREATE FUNCTION

postgres=#

postgres=# select system('pg_dump -s -t orasup_test1 dbinfo2 |egrep -v "^--|^$"');
                       system                        
-----------------------------------------------------
 SET statement_timeout = 0;                         +
 SET lock_timeout = 0;                              +
 SET idle_in_transaction_session_timeout = 0;       +
 SET client_encoding = 'UTF8';                      +
 SET standard_conforming_strings = on;              +
 SET check_function_bodies = false;                 +
 SET client_min_messages = warning;                 +
 SET row_security = off;                            +
 SET search_path = public, pg_catalog;              +
 SET default_tablespace = '';                       +
 SET default_with_oids = false;                     +
 CREATE TABLE orasup_test1 (                        +
     a integer,                                     +
     b character varying(200)                       +
 );                                                 +
 ALTER TABLE orasup_test1 OWNER TO djidba_rw;       +
 CREATE INDEX idx_b ON orasup_test1 USING btree (b);+
 
(1 row)

postgres=# 
postgres=#

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postgres=# select system('pg_dump -s -t orasup_test1 dbinfo2 |egrep -v "^--|^$"');

system

-----------------------------------------------------

SET statement_timeout = 0; +

SET lock_timeout = 0; +

SET idle_in_transaction_session_timeout = 0; +

SET client_encoding = 'UTF8'; +

SET standard_conforming_strings = on; +

SET check_function_bodies = false; +

SET client_min_messages = warning; +

SET row_security = off; +

SET search_path = public, pg_catalog; +

SET default_tablespace = ''; +

SET default_with_oids = false; +

CREATE TABLE orasup_test1 ( +

a integer, +

b character varying(200) +

); +

ALTER TABLE orasup_test1 OWNER TO djidba_rw; +

CREATE INDEX idx_b ON orasup_test1 USING btree (b);+

(1 row)

postgres=#

Study note

pg常用大小查询

2020-09-24 没有评论

查出所有数据库大小：

select pg_database.datname, pg_database_size(pg_database.datname) AS size from pg_database order by size desc;

1	select pg_database.datname, pg_database_size(pg_database.datname) AS size from pg_database order by size desc;

查出所有表按大小排序并分离data与index：

SELECT
    table_name,
    pg_size_pretty(table_size) AS table_size,
    pg_size_pretty(indexes_size) AS indexes_size,
    pg_size_pretty(total_size) AS total_size
FROM (
    SELECT
        table_name,
        pg_table_size(table_name) AS table_size,
        pg_indexes_size(table_name) AS indexes_size,
        pg_total_relation_size(table_name) AS total_size
    FROM (
        SELECT ('"' || table_schema || '"."' || table_name || '"') AS table_name
        FROM information_schema.tables
    ) AS all_tables
    ORDER BY total_size DESC
) AS pretty_sizes;

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SELECT

table_name,

pg_size_pretty(table_size) AS table_size,

pg_size_pretty(indexes_size) AS indexes_size,

pg_size_pretty(total_size) AS total_size

FROM (

SELECT

table_name,

pg_table_size(table_name) AS table_size,

pg_indexes_size(table_name) AS indexes_size,

pg_total_relation_size(table_name) AS total_size

FROM (

SELECT ('"' || table_schema || '"."' || table_name || '"') AS table_name

FROM information_schema.tables

) AS all_tables

ORDER BY total_size DESC

) AS pretty_sizes;

查看索引大小：

select relname as table_name,pg_size_pretty(pg_relation_size(relid)) as table_size, 
indexrelname as index_name,
pg_size_pretty(pg_relation_size(indexrelid)) as index_size from pg_stat_user_indexes 
order by pg_relation_size(indexrelid) desc;

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select relname as table_name,pg_size_pretty(pg_relation_size(relid)) as table_size,

indexrelname as index_name,

pg_size_pretty(pg_relation_size(indexrelid)) as index_size from pg_stat_user_indexes

order by pg_relation_size(indexrelid) desc;

Study note

小记MySQL的锁和事务

2019-11-20 没有评论

（一）先说明一下定义： 1. 读现象（Read phenomena）： SQL 92标准规定了3种不同的读现象。脏读、不可重复读和幻读。分别解释一下。 1.1 脏读： A dirty read (aka uncommitted dependency) occurs when a transactio […]

Study note

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 […]

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 […]

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 […]

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 […]

Study note

官方推荐的MySQL参数设置值

2018-01-31 一条评论

今天，在找MySQL补丁的时候，在metalink找到一篇非常好的文章。这oracle官方推荐的在OLTP环境下，MySQL参数设置的最佳实践。下面的参数设置，对系统的性能会很有帮助。但是建议大家还是结合实际情况使用。 APPLIES TO: MySQL Server – Versio […]

Study note

Oracle 12.2 新特性介绍

2017-10-25 没有评论

计划明年等12.2.0.2出来之后，在公司全面推行oracle 12.2版本数据库。在此之前，为了团队做好知识储备，总结了一下12.2的新特性，进行宣讲。【PDF下载】：Oracle 12.2新特性介绍

Study note

远程数据库的表超过20个索引的影响

2017-09-24 一条评论

昨天同事参加了一个研讨会,有提到一个案例。一个通过dblink查询远端数据库，原来查询很快，但是远端数据库增加了一个索引之后，查询一下子变慢了。经过分析，发现那个通过dblink的查询语句，查询远端数据库的时候，是走索引的，但是远端数据库添加索引之后，如果索引的个数超过20个，就会忽略第一个建立的 […]