Check database uptime

Sometimes you have to check when a database was started for the last time. To get the information, just log on to the database and use the following query to get the last startup time:

On Oracle database

SELECT to_char(startup_time,'DD-MON-YYYY HH24:MI:SS') AS "DB Startup Time"
FROM   sys.v_$instance;

On Mysql database

SHOW GLOBAL STATUS LIKE 'Uptime';

This simple trick can be useful to troubleshoot when a database was unavaliable at some point and is now accessible. Using this simple command you’ll be able to tell if the database has been restarted.

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Rename a Postgresql database

#database #postgresql

Here's the procedure to rename a PostgreSQL database: 1. Disconnect from the database that you want to rename and connect to a different database. 2. Check and terminate all active connections to the database that you want to rename. 3. Use the `ALTER DATABASE` statement to rename the database to the new one. Let’s take a look at an example of... Read more

20 May 2019 - 1 minute read

How to duplicate a Postgresql database

#database #postgresql

If you need to duplicate an existing Postgresql database, and possibly transfer ownership of the database objects to a new user, here's how to do that in a quick way: ```sql -- First, I recommand getting the size of the database to copy, as this might be important for the rest of the process. SELECT pg_database.datname,pg_size_pretty(pg_databas... Read more

20 Apr 2019 - less than 1 minute read

Forcing ASMM component to shrink

#oracle #database

Here's the way to force the shared pool to shrink dynamically. Documentation states that ASMM can only increase shared pool, and can't shrink. When the automatic shared memory management feature is enabled, the internal tuning algorithm tries to determine an optimal size for the shared pool based on the workload. It usually converges on this va... Read more

20 Mar 2019 - 2 minute read

Forcing ASMM component to shrink

#oracle #database

Here's the way to force the shared pool to shrink dynamically. Documentation states that ASMM can only increase shared pool, and can't shrink. When the automatic shared memory management feature is enabled, the internal tuning algorithm tries to determine an optimal size for the shared pool based on the workload. It usually converges on this va... Read more

20 Mar 2019 - 2 minute read

How to extract Oracle user DDL

#database #oracle

In some cases, you need to duplicate an Oracle user, along with all it's privileges. Doing this manually can be tedious. Hopefully, we can use the data dictionary to extract the data we need and dump it into a SQL file to modify and replay. Here's how to do it: ```sql set head off set pages 0 set long 9999999 spool user_script.sql SELECT DBMS... Read more

20 Feb 2018 - 1 minute read

Restart a hung Oracle database

#oracle

On rare occasions, mostly during a high server load peak or a process failure, an Oracle instance may not accept any connection. Either from regular users as well as SYSDBA. This situation is called a **hung database** and must be quickly resolved as the database isn't accessible for your users anymore. As you cannot connect to the hung database... Read more

20 May 2017 - 1 minute read

Last rowcount in MySQL

#mysql

Suppose you want to count the number of lines returned by the last SQL statement issued. For **select** statements you can use the *FOUND_ROWS* construct: ```sql SELECT SQL_CALC_FOUND_ROWS something FROM your_table WHERE whatever; SELECT FOUND_ROWS(); ``` This will return the number of rows in the last **select** query (or if the first query ... Read more

20 Sep 2016 - less than 1 minute read

MySQL punch user creation DDL

#mysql

You can get the DDL necessary to duplicate an existing user with the following system command: ``` MYSQL_CONN="-uroot -ppassword" mysql ${MYSQL_CONN} --skip-column-names -A -e "SELECT CONCAT('SHOW GRANTS FOR ''',user,'''@''',host,''';') FROM mysql.user WHERE user'' " | mysql ${MYSQL_CONN} --skip-column-names -A | sed 's/$/;/g' > MySQLUserGrants... Read more

20 Jul 2016 - less than 1 minute read

InnoDB table rebuild

#mysql

### PROBLEM On a **MySQL 5.6** database server, the *ibdata1* file includes 5 InnoDB tables in the mysql schema. ```sql mysql> select table_name from information_schema.tables -> where table_schema='mysql' and engine='InnoDB'; +----------------------+ | table_name | +----------------------+ | innodb_index_stats | | innodb_table... Read more

20 Jun 2016 - 1 minute read