Skip to main content

Persisting Data and Replication in Redis

As we know, Redis is an in-memory key-value store database. If our data is stored in our host memory (RAM), how can we restore all values from the last state of our system in case of system reboot or power outages?

Redis provides two options for persisting our data. The first is by creating a snapshot and the second is by appending each write action into a file. The second is also called the append-only-file (AOF) method. Applying those options is as trivial as updating several lines of the Redis configuration file.

Redis performs snapshotting with certain rules by default. Enabling the auto-snapshot method with different rules is done by configuring the following lines in the /etc/redis/redis.conf file.

save 300 10
save 30 1000
stop-writes-on-bgsave-error yes
rdbcompression yes
rdbchecksum yes
dbfilename dump.rdb
dir /var/lib/redis

The line save 300 10 means snapshot will be automatically updated in the background if at least 10 writes have occurred within 300 seconds. The line save 30 1000 means it will be updated for at least 1000 writes within 30 seconds.

Snapshotting is also run by Redis automatically when it is shutting down gracefully. We can also run BGSAVE or SAVE command on Redis client. The BGSAVE command will run snapshotting process by initiating a fork of the main Redis thread so it won't block Redis to accept any writes from the client. Auto-snapshotting is also run this way. But, we need to consider the available memory of our host for performing this action because current values in our database will be buffered in memory before they can be written in the RDB file. Meanwhile, the SAVE command is run on the main thread so it will block Redis from accepting any write.

Append-only mode works differently, it captures any writes and appends them into the appendonly.aof file. Several configuration options are as follows.

appendonly yes
appendfilename "appendonly.aof"
appendfsync everysec
no-appendfsync-on-rewrite yes

The appendfsync parameter has three options: always, everysec, and no. The everysec option won't make Redis appends each of the new writes directly as it happens but Redis will aggregate them and append them one time on every second. Appending process can also be triggered by running the BGREWRITEAOF command on the Redis client.

Database replication is also very trivial as Redis support it on its core. When we have a primary/master Redis instance, we can deploy another Redis instance and assign it as a replica/slave of the primary one. In the replica server configuration, we can add a parameter replicaof <masterhost> <port>. By default, the replica is read-only. We can add a parameter replica-read-only no if we want to enable writing on the replica. But, it is only for ephemeral or temporary data because the stored values will be rewritten when the replica resync with the primary one.



Comments

Popular posts from this blog

Configuring Swap Memory on Ubuntu Using Ansible

If we maintain a Linux machine with a low memory capacity while we are required to run an application with high memory consumption, enabling swap memory is an option. Ansible can be utilized as a helper tool to automate the creation of swap memory. A swap file can be allocated in the available storage of the machine. The swap file then can be assigned as a swap memory. Firstly, we should prepare the inventory file. The following snippet is an example, you must provide your own configuration. [server] 192.168.1.2 [server:vars] ansible_user=root ansible_ssh_private_key_file=~/.ssh/id_rsa Secondly, we need to prepare the task file that contains not only the tasks but also some variables and connection information. For instance, we set /swapfile  as the name of our swap file. We also set the swap memory size to 2GB and the swappiness level to 60. - hosts: server become: true vars: swap_vars: size: 2G swappiness: 60 For simplicity, we only check the exi

Master Slave Replication to Automatically Backup Your MySQL Database

We can make backup for some databases by periodically running a kind of dump query, like mysqldump in MySQL. That's the simplest method but it can drain our server resources and it's not suitable for large databases. MySQL comes up with master-slave features that allow you to replicate your database to another location (slave). This mechanism enables MySQL to generate a log file which records any action performed to the database. Then, that action will be run in slave database too. For example, we have two database servers with IP address 192.168.0.1 (Master) and 192.168.0.2 (Slave). 1) Configure my.cnf in master server # Master Settings # locate where the changes record will be stored log-bin = /var/log/mysql/mysql-bin.log # set unique ID for master database in master-slave network (up to you) server-id = 111 innodb_flush_log_at_trx_commit = 1 sync_binlog = 1 # select database which will be replicated # by default system will log all databases binlog-do-db =

Installing VSCode Server Manually on Ubuntu

I've ever gotten stuck on updating the VSCode server on my remote server because of an unstable connection between my remote server and visualstudio.com that host the updated server source codes. The download and update process failed over and over so I couldn't remotely access my remote files through VSCode. The solution is by downloading the server source codes through a host with a stable connection which in my case I downloaded from a cloud VPS server. Then I transfer the downloaded source codes as a compressed file to my remote server through SCP. Once the file had been on my remote sever, I extracted them and align the configuration. The more detailed steps are as follows. First, we should get the commit ID of our current VSCode application by clicking on the About option on the Help menu. The commit ID is a hexadecimal number like  92da9481c0904c6adfe372c12da3b7748d74bdcb . Then we can download the compressed server source codes as a single file from the host.

Resize VirtualBox LVM Storage

VirtualBox is a free solution to host virtual machines on your computer. It provides configuration options for many components on our machine such as memory, storage, networking, etc. It also allows us to resize our machine storage after its operating system is installed. LVM is a volume manager in a Linux platform that helps us to allocate partitions in the system and configure the storage size that will be utilized for a specific volume group. There are some points to be noticed when we work with LVM on VirtualBox to resize our storage. These are some steps that need to be performed. 1. Stop your machine before resizing the storage. 2. Set new storage size using GUI by selecting " File > Virtual Media Manager > Properties " then find the desired virtual hard disk name that will be resized. OR , by running a CLI program located in " Program Files\Oracle\VirtualBox\VBoxManage.exe ".  cd "/c/Program Files/Oracle/VirtualBox" ./VBoxManage.exe list

Rangkaian Sensor Infrared dengan Photo Dioda

Keunggulan photodioda dibandingkan LDR adalah photodioda lebih tidak rentan terhadap noise karena hanya menerima sinar infrared, sedangkan LDR menerima seluruh cahaya yang ada termasuk infrared. Rangkaian yang akan kita gunakan adalah seperti gambar di bawah ini. Pada saat intensitas Infrared yang diterima Photodiode besar maka tahanan Photodiode menjadi kecil, sedangkan jika intensitas Infrared yang diterima Photodiode kecil maka tahanan yang dimiliki photodiode besar. Jika  tahanan photodiode kecil  maka tegangan  V- akan kecil . Misal tahanan photodiode mengecil menjadi 10kOhm. Maka dengan teorema pembagi tegangan: V- = Rrx/(Rrx + R2) x Vcc V- = 10 / (10+10) x Vcc V- = (1/2) x 5 Volt V- = 2.5 Volt Sedangkan jika  tahanan photodiode besar  maka tegangan  V- akan besar  (mendekati nilai Vcc). Misal tahanan photodiode menjadi 150kOhm. Maka dengan teorema pembagi tegangan: V- = Rrx/(Rrx + R2) x Vcc V- = 150 / (150+10) x Vcc V- = (150/160) x 5

Setting Up Next.js Project With ESLint, Typescript, and AirBnB Configuration

If we initiate a Next.js project using the  create-next-app tool, our project will be included with ESLint configuration that we can apply using yarn run lint . By default, the tool installs eslint-config-next and extends next/core-web-vitals in the ESLint configuration. The Next.js configuration has been integrated with linting rules for React and several other libraries and tools. yarn create next-app --typescript For additional configuration such as AirBnB, it is also possible. First, we need to install the peer dependencies of eslint-config-airbnb . We also add support for Typescript using eslint-config-airbnb-typescript . yarn add --dev eslint-config-airbnb eslint-plugin-import eslint-plugin-jsx-a11y eslint-plugin-react eslint-plugin-react-hooks yarn add --dev eslint-config-airbnb-typescript @typescript-eslint/eslint-plugin @typescript-eslint/parser After that, we can update the .eslintrc.json file for the new configuration. { "extends": [ "airb