swap memory

Document/content/faqs/qitmeer-token-issurance/_index.en.md → Document/content/faqs/qitmeer-token-issuance/_index.en.md

@@ -1,8 +1,8 @@
 ---
-title:  Qitmeer Token Issurance
+title:  Qitmeer Token Issuance
 weight: 5
 #pre: "<b>1. </b>"
 # chapter: true
 ---
 
-Qitmeer assets issurance componet, OP_TOKEN, is based on UTXO (Unspent Transaction Output) transaction model, to support massive islamic economic liquidity. OP_TOKEN ensures assets backed by native currency and requires authority-owned licenses to publish assets, which is designed for sharia consideration scenarios.
+Qitmeer assets issuance component, OP_TOKEN, is based on UTXO (Unspent Transaction Output) transaction model, to support massive islamic economic liquidity. OP_TOKEN ensures assets backed by native currency and requires authority-owned licenses to publish assets, preventive from .

Document/content/tutorials/_index.en.md

@@ -20,3 +20,5 @@ weight: 3
 - [Qitmeer Wallet Rpc Guide](./qitmeer-wallet-rpc)
 
 - [Qitmeer JS Guide](./qitmeer-js)
+
+- [Mount Swap Memory](./swap-memory)

Document/content/tutorials/swap-memory/_index.en.md

@@ -0,0 +1,78 @@
+---
+title: Swap Memory
+weight: 1
+#pre: "<b>1. </b>"
+# chapter: true
+---
+
+This tutorial instructs qitmeer node maintainers to mount swap memory to solve the Out of Memory problem.
+
+## Problem Description
+Qitmeer's recommended memory perquisite is 2GB, 1 GB at minimum. Even though memory has satisfied the recommended requirement, it is still possible that Qitmeer gets killed by system due to peak usage of memory, called Out of Memory exception.
+
+```sh
+2021-03-23|07:45:22.110 [INFO ] Processed 211 blocks in the last 10s (217 transactions, order 283091, 2020-09-27 15:05:08 +0800 CST) module=blkmanager
+[1]    196072 killed     ./build/bin/qitmeer
+
+```
+
+You may confirm this exception by the command:
+
+> Note: assume OS is Ubuntu
+
+```sh
+dmesg -T| grep -E -i -B100 'killed process'
+```
+If you find similar output as follows, then that maybe the case
+```sh
+[Tue Mar  9 11:34:26 2021] Out of memory: Killed process 140587 (qitmeer) total-vm:1403144kB,
+anon-rss:675828kB, file-rss:0kB, shmem-rss:0kB, UID:1001 pgtables:1532kB oom_score_adj:0
+```
+
+## Solution
+### What is Swap Memory
+OS could transfer inactive memory into hard disk to make room for active processes, called memory swapping. Although this mechanism would reduce the overall performance of  machines due to high swapping cost between physical memory and virtual memory (hard disk), it brings stronger stability.
+
+## How to mount swap memory
+> Note: Ensure you have root permission
+
+1. create folder for swap file
+
+```bash
+root@Qit:/home/tony$ cd /
+root@Qit:/$ mkdir swap
+root@Qit:/$ cd swap/
+```
+
+2.  create a 2GB swap file
+```bash
+root@Qit:/swap$ dd if=/dev/zero of=SWAPFILE bs=1024 count=2097152
+2097152+0 records in
+2097152+0 records out
+2147483648 bytes (2.1 GB, 2.0 GiB) copied, 14.838 s, 145 MB/s
+```
+
+3. convert into swap format 
+```sh
+root@Qit:/swap$ mkswap SWAPFILE 2097152
+mkswap: SWAPFILE: insecure permissions 0644, 0600 suggested.
+Setting up swapspace version 1, size = 2 GiB (2147479552 bytes)
+no label, UUID=06ee7e99-ab8f-4378-b0d0-3f5477bd1090
+```
+
+4. format swap file
+```sh
+root@Qit:/swap$ swapon SWAPFILE
+swapon: /swap/SWAPFILE: insecure permissions 0644, 0600 suggested.
+```
+check swap file usage
+```sh
+root@Qit:/swap$ free
+              total        used        free      shared  buff/cache   available
+Mem:         980192      271480       63400        2676      645312      545572
+Swap:       2097148           0     2097148
+```
+5. auto mount swap file on booting
+```sh
+root@Qit:~$ echo "/swap/SWAPFILE swap swap defaults 0 0" >> /etc/fstab
+```