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

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

Kerusakan pada Motherboard

1. Sering terjadi hang memory tidak cocok --- ganti memory ada virus di harddisk --- scan harddisk over clock --- seting kembali clock prosesor ada bad sector di harddisk --- partisi harddisk dengan benar 2. Pembacaan data menjadi lambat memori tidak cukup --- tambah memori harddisk penuh atau ada virus --- kurangi isi harddisk, scan harddisk, atau ganti hardisk 3. CMOS failure baterai habis --- ganti baterai CMOS seting BIOS berubah --- seting kembali BIOS 4. Tidak bisa booting cache memory rusak --- disable eksternal cache memory di BIOS memori tidak cocok --- ganti memori boot sector pada harddisk rusak --- masukkan operating system baru ada bad sector pada trek awal harddisk --- partisi harddisk 5. Suara bip panjang berkali-kali memori rusak --- periksa kedudukan memori memori tidak cocok --- ganti memori memori tidak masuk slot dengan sempurna --- periksa kembali kedudukan memori 6. Suara bip bagus tetapi tidak ada tampilan / bip dua kali VGA card

Raspberry Pi Bluetooth Connection

Raspberry Pi 3 provides a built-in Bluetooth module. The latest Raspbian has been bundled with tools for enabling Bluetooth connection. The Bluetooth icon will be shown up on the top right corner of the desktop. It's a tool to discover available Bluetooth devices and connect Pi with Bluetooth devices. It is easy to connect any Bluetooth-enabled electronic device with Pi. But, sometimes Pi will fail to connect, especially for Bluetooth device that has no standardized services. From a terminal, we can use the  bluetoothctl tool to scan and connect with a Bluetooth device. You should make sure that the BlueZ protocol stack has been installed by running $ apt-get install bluez Run bluetoothctl to enter the tool command window Turn the power on by running power on (Optional) You can set AutoEnable=true in /etc/bluetooth/main.conf if you want to make the Bluetooth auto power-on after reboot. Run devices to see which devices have been paired Run scan on if your desired d

How To Use Git in Netbeans

Git is a popular version control application nowadays. Recently I have created a note about its differences with SVN and how to use it in Eclipse . There are many Git client tools. But I just want to show how to use Netbeans built-in Git tools. It makes the development process easier because it has been integrated with the IDE. Create Remote Git Repository We need a remote Git repository so everyone can store or receive any revision or updated files through the networks. We can set up our own Git server or use a public Git server like Github . In this note, I use Github. 1. Create an account in Github and create an empty Git repository Create an empty public repository in Github 2. Get the remote repository link Your Github Repository URL Create a New Project in Netbeans and Create Local Git Repository After we have a remote Git repository, we can create a project stored in the remote repository. We also need to create a local repository before we can push

I Love Books

I like reading books since I was a kid. Thanks to my parents that let me bought any books and embraced me to read. Bookstore becomes one of my favorite places. I like to learn any topics, not only about science or IT stuffs. For me, reading a book isn't always intended to have possession in the topic, but it's for my personal pleasure and building an insight of something. some of them There're many things around us that we don't understand really well. If we try to figure it out by ourselves, we will waste most of our precious time. So, it's better to learn from the expert who has studied it well and then considering it with our common sense and logic. I grow up, many affairs had occurred, and shit happens. I realize that I have forgotten a lot of things. I likely tend to be aware of fewer things. So let me open a cupboard full of books which I've collected since a long time ago.