| 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 |
Picking the right architecture = Picking the right battles + Managing trade-offs
- Clarify and agree on the scope of the system
- User cases (description of sequences of events that, taken together, lead to a system doing something useful)
- Who is going to use it?
- How are they going to use it?
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
When hosting our web applications, we often have one public IP
address (i.e., an IP address visible to the outside world)
using which we want to host multiple web apps. For example, one
may wants to host three different web apps respectively for
example1.com, example2.com, and example1.com/images on
the same machine using a single IP address.
How can we do that? Well, the good news is Internet browsers
Just run this from your Mac terminal and it'll drop you in a container with full permissions on the Docker VM. This also works for Docker for Windows for getting in Moby Linux VM (doesn't work for Windows Containers).
docker run -it --rm --privileged --pid=host justincormack/nsenter1
more info: https://github.com/justincormack/nsenter1
| node { | |
| echo 'Results included as an inline comment exactly how they are returned as of Jenkins 2.121, with $BUILD_NUMBER = 1' | |
| echo 'No quotes, pipeline command in single quotes' | |
| sh 'echo $BUILD_NUMBER' // 1 | |
| echo 'Double quotes are silently dropped' | |
| sh 'echo "$BUILD_NUMBER"' // 1 | |
| echo 'Even escaped with a single backslash they are dropped' | |
| sh 'echo \"$BUILD_NUMBER\"' // 1 | |
| echo 'Using two backslashes, the quotes are preserved' | |
| sh 'echo \\"$BUILD_NUMBER\\"' // "1" |
• 45-minute systems interview, focus on responding to real world problems with an unhealthy service, such as a web server or database. The interview will start off at a high level troubleshooting a likely scenario, dig deeper to find the cause and some possible solutions for it. The goal is to probe your knowledge of systems at scale and under load, so keep in mind the challenges of the Facebook environment.
• Focus on things such as tooling, memory management and unix process lifecycle.
More specifically, linux troubleshooting and debugging. Understanding things like memory, io, cpu, shell, memory etc. would be pretty helpful. Knowing how to actually write a unix shell would also be a good idea. What tools might you use to debug something? On another note, this interview will likely push your boundaries of what you know (and how to implement it).
Interview is all about taking an ambiguous question of how you might build a system and letting
| ''' | |
| Basic tail command implementation | |
| Usage: | |
| tail.py filename numlines | |
| ''' | |
| import sys | |
| import linecache |