BlackHC

Latency Comparison Numbers (~2023)
----------------------------------
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 Snappy            3,000   ns        3 µs
Read 1 MB sequentially from memory      20,000   ns       20 µs          ~50GB/sec DDR5
Read 1 MB sequentially from NVMe       100,000   ns      100 µs          ~10GB/sec NVMe, 5x memory

psayre23

Below are the Big O performance of common functions of different Java Collections.


List                 | Add  | Remove | Get  | Contains | Next | Data Structure
---------------------|------|--------|------|----------|------|---------------
ArrayList            | O(1) |  O(n)  | O(1) |   O(n)   | O(1) | Array
LinkedList           | O(1) |  O(1)  | O(n) |   O(n)   | O(1) | Linked List
CopyOnWriteArrayList | O(n) |  O(n)  | O(1) |   O(n)   | O(1) | Array

trongthanh

# source: http://st-on-it.blogspot.com/2010/01/how-to-move-folders-between-git.html
# First of all you need to have a clean clone of the source repository so we didn't screw the things up.

git clone git://server.com/my-repo1.git

# After that you need to do some preparations on the source repository, nuking all the entries except the folder you need to move. Use the following command

git filter-branch --subdirectory-filter your_dir -- -- all

# This will nuke all the other entries and their history, creating a clean git repository that contains only data and history from the directory you need. If you need to move several folders, you have to collect them in a single directory using the git mv command.