My Scribbles

Muscle Memory Makeover

Docker just streamlined Docker Compose by integrating it as a plugin. Great news, but it means us old hats need to retrain our fingers. Here's a quick fix for your .bashrc to keep things smooth:

alias docker-compose='docker compose'

MySQL in a Flash

As a programmer and Linux admin, I juggle multiple MySQL servers with different group suffixes. Typing --defaults-group-suffix every time was a drag. This handy bash function saves the day:

m() {
  mysql --defaults-group-suffix=$1
}

Now, connecting to a database is as easy as:

m specific-suffix

This keeps your workflow concise and saves you precious keystrokes. Put them into you .bashrc or .zshrc now and let our life easier!

You want to add a unique index to a table, and unfortunately, there are already many duplicate rows in it. Manually find and delete these rows is time-wasting and error-prone. So why won't we just write one SQL statement and quickly resolve it?

First try, I wrote the following statement, and it won't work:

DELETE FROM PromotionSkus A 
WHERE 
	A.SkuId IN (SELECT SkuId FROM PromotionSkus B GROUP BY B.SkuId HAVING COUNT(B.SkuId) > 1) 
	AND 
	A.Id NOT IN (SELECT MIN(Id) FROM PromotionSkus C GROUP BY C.SkuId HAVING COUNT(C.SkuId) > 1);

AND this one below works!

DELETE FROM PromotionSkus A
WHERE 
	A.Id NOT IN (SELECT Id FROM (SELECT MIN(Id) AS Id, COUNT(SkuId) AS Total FROM PromotionSkus GROUP BY SkuId HAVING Total > 1) AS B)
	AND 
	A.SkuId IN (SELECT SkuId FROM (SELECT SkuId FROM PromotionSkus GROUP BY SkuId HAVING COUNT(SkuId) > 1) AS C);

The reason is well explained in this brilliant article.

Another mysql tip: using mysqldump export a table with one line one row.

mysqldump --databases YourDataBaseName --tables YourTableName --skip-extended-insert

Why do we need that? It is much easier to compare !

1. put a .my.cnf file into your home directory, for example

$ cat ~/.my.cnf 
[client]
user=yourDbUserName
password=yourDbPassword
host=yourDbHost

2. write a bash script to update the database

#!/bin/bash

set -ex

variable=`TZ="Africa/Abidjan" date '+%Y-%m-%d %H:%M:%S'`
sql="Your SQL statement with ${variable}"

logDir=/data/Logs/`date '+%Y'`/`date '+%m'`
mkdir -p "${logDir}"
echo "${sql}" >> "${logDir}/`date '+%d'`.sql"
mysql -v -v -e "${sql}" >> "${logDir}/`date '+%d'`.result.txt"

3. put a line by run crontab -e

the end.

1. on a server with huge disk space, run crontab -e and put the following code in it (you may need to change the directory names to fit your situation)

   30 3 * * * mysqldump --databases DB1 DB2 DB3 DB4 | gzip > /data/backups/mysql/db_`date '+\%Y\%m\%d-\%H\%M\%S'`.sql.gz
   30 4 * * * find /data/backups/mysql/db_* -mtime -1 -exec scp {} anotherserver:/data/backups/mysql \;
   30 5 * * * find /data/backups/mysql/db_* -mtime +30 -exec rm {} \;
   

2. on another server, run crontab -e and put the following line into it:

   30 5 * * * find /data/backups/mysql/db_* -mtime +7 -exec rm {} \;
   

summary & explanation:

1. at 3:30 backup MySQL data in a local directory and keep latest 30 days backup in that directory
2. at 4:30 transfer the latest backup to another server in case the first backup may be destroyed by an accident.
3. at 5:30 remove the oldest backup on the local backup server (the code shows that the latest 30 days backups are kept on the server).
4. at 5:30 remove the oldest backup on the remote server (the code shows that only the latest 7 days backups are kept on that server).