I have moved this over to the Tech Interview Cheat Sheet Repo and has been expanded and even has code challenges you can run and practice against!
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# This is an example of the Stack Exchange Tier 1 HAProxy config | |
# The only things that have been changed from what we are running are: | |
# 1. User names have been removed | |
# 2. All Passwords have been remove | |
# 3. IPs have been changed to use the example/documentation ranges | |
# 4. Rate limit numbers have been changed to randome numbers, don't read into them | |
userlist stats-auth | |
group admin users $admin_user | |
user $admin_user insecure-password $some_password |
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Use tcpdump to monitor mysql | |
# Capture the packets | |
sudo tcpdump -i eth0 port 3306 -s 65535 -x -n -q -tttt > tcpdump.out | |
# analyze all the requests from a given host | |
pt-query-digest --type=tcpdump --filter '($event->{host} || $event->{ip} || "") =~ m/192.168.248.64/' tcpdump.out |
L1 cache reference ......................... 0.5 ns
Branch mispredict ............................ 5 ns
L2 cache reference ........................... 7 ns
Mutex lock/unlock ........................... 25 ns
Main memory reference ...................... 100 ns
Compress 1K bytes with Zippy ............. 3,000 ns = 3 µs
Send 2K bytes over 1 Gbps network ....... 20,000 ns = 20 µs
SSD random read ........................ 150,000 ns = 150 µs
Read 1 MB sequentially from memory ..... 250,000 ns = 250 µs
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Latency Comparison Numbers (~2012) | |
---------------------------------- | |
L1 cache reference 0.5 ns | |
Branch mispredict 5 ns | |
L2 cache reference 7 ns 14x L1 cache | |
Mutex lock/unlock 25 ns | |
Main memory reference 100 ns 20x L2 cache, 200x L1 cache | |
Compress 1K bytes with Zippy 3,000 ns 3 us | |
Send 1K bytes over 1 Gbps network 10,000 ns 10 us | |
Read 4K randomly from SSD* 150,000 ns 150 us ~1GB/sec SSD |
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