Recover deleted file from Git

To recover an old file from git where you don’t know the commit, you can do:

git checkout $(git rev-list -n 1 HEAD -- "$file")^ -- "$file"

Finds the last commit that affected the given path and checks out the file from there. Works on any file still in the history. If the file has not been staged or committed, simply use git checkout $file.

From: SO

Redis database size and key info

You can use INFO to get total memory size and a lot of other useful bits but if you just want to know the size of a single database or other info about database-specific keys, it can be a bit tricky.

see: https://stackoverflow.com/questions/7638542/redis-show-database-size-size-for-keys

tldr; in many cases, all you might need is:

redis-cli --bigkeys

To see what’s going on real-time:

redis-cli MONITOR

Yii2 fix “Malformed UTF-8 characters” error with master/slave db

You need to specify charset in slave config, e.g.,

'slaveConfig' => [
  'charset' => 'utf8',
  ...

Docker for Mac fix for max files, transparent hugepages warnings

To avoid Redis and other apps’ “max files limit” and “transparent hugepages” etc errors in Docker containers on Docker for Mac, you can set sysctls options in your docker-compose file by using compose format 2.1 or greater, which should be supported in docker-compose >= 1.10.

in docker-compose.yml file:

version: '2.1'
services:
  redis:
    image: redis:3.2-alpine
    command: redis-server /usr/local/etc/redis/redis.conf
    sysctls:
      - net.core.somaxconn=1024

To update transparent hugepages settings in Docker for Mac’s Alpine hypervisor host system, you can use this hack:

docker run --rm --privileged -ti alpine /bin/sh -c "echo never > /sys/kernel/mm/transparent_hugepage/enabled && echo never > /sys/kernel/mm/transparent_hugepage/defrag"

In theory you wouldn’t need/want to do this on a production host as you would configure the host properly. If you update Docker, you will need to re-run this.

Sysctl optimization updates for Redis, MongoDB, etc.

Sysctl Performance tips for Redis, MongoDB, etc.

# backup:
$ sysctl -a > /home/sysctl_$(date +%Y%m%d).bak
#check:
$ sysctl -a
 
# make changes to sysctl.conf:
$ vi/nano /etc/sysctl.conf
 
# web - nginx, redis, mongo, etc:
vm.swappiness = 10
vm.dirty_ratio = 40
vm.dirty_background_ratio = 10
# for larger servers:
net.ipv4.tcp_rmem = 4096 12582912 33554432
net.ipv4.tcp_wmem = 4096 12582912 33554432
net.core.rmem_max = 33554432
net.core.wmem_max = 33554432
net.ipv4.tcp_window_scaling = 1
net.ipv4.tcp_timestamps = 1
net.ipv4.tcp_sack = 1
#
net.ipv4.tcp_max_syn_backlog = 65536
kernel.keys.root_maxkeys = 1000000
#Raise somaxconn (above 511)
net.core.somaxconn = 4096
 
# vm.overcommit_memory (optional):
# vm.overcommit_memory = 1
####
 
# set in /etc/rc.local (test reboot stickiness)
# ensure changes to sysctl configuration persist across reboots:
$ sysctl -p
 
if test -f /sys/kernel/mm/transparent_hugepage/enabled; then
   echo never > /sys/kernel/mm/transparent_hugepage/enabled
fi
if test -f /sys/kernel/mm/transparent_hugepage/defrag; then
   echo never > /sys/kernel/mm/transparent_hugepage/defrag
fi

more info:

  • https://wiki.mikejung.biz/Sysctl_tweaks
  • https://www.techandme.se/performance-tips-for-redis-cache-server/
  • https://unix.stackexchange.com/questions/99154/disable-transparent-hugepages
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