notes blog about

big data

The idea that large databases of seemingly random data about people (ex. purchasing habits, location information) are valueable.

binary data

Data represented in binary form rather than interpreted on higher level or converted to some other form. While most binary data has symbolic meaning not all binary data is numeric (ex. computer instructions within processor registers).

block size

The POSIX standard defines a block size of 512 bytes. However, this size is harder to read, so by default, the df and du output in most Linux distributions is in 1024-byte blocks.


means that data likely to be used in the future is kept “nearby”


cloud native

Cloud native technologies empower organizations to build and run scalable applications in modern, dynamic environments such as public, private, and hybrid clouds…. These techniques enable loosely coupled systems that are resilient, manageable, and observable. Combined with robust automation, they allow engineers to make high-impact changes frequently and predictably with minimal toil.

– Cloud Native Computing Foundation, CNCF Cloud Native Definition v1.0



Qualitative or quantitative facts about things. Information and then knowledge are derived from data.

directory permissions

You can list the contents of a directory if it’s readable (r), but you can only access a file in a directory if the directory is executable (x). Typical (absolute) permission modes for directories: 755, 700, 711.


literally, the love of wisdom; the science that seeks to understand all things by knowing their causes by natural reason


A form of database. It supplies the structure to transform a simple block device into the sophisticated hierachy of files and subdirectories that users can understand.

first-class functions

In a language with first-class functions, functions can be assigned to variables, and then called later using those variables.

Functions can also be passed as arguments when calling other functions.

fstab fields

<...> 0 1


In a typical database, it’s an internal structure that is used to increase the speed of data retrieval. It’s a copy of selected data that can be searched very efficiently, which might also include a file-level disk block number or even a direct connection to the entire set of data it was copied from.


create an object from the class, ex.

class Eyes(object):

    def __init__(self, color='brown'):
        self.color = color

    def print_color(self):
        print("Eyes are", self.color)

eyes_obj = Eyes(color='blue')  # instantiation

IPv4 address classes

| Class | First octet | Networks                  | Number of networks | Purpose                         |
| A     | 1   - 126   |   -     | 2^7 - 2 = 126      | Unicast (large networks)        |
| B     | 128 - 191   | -   | 2^14 = 16,384      | Unicast (medium-sized networks) |
| C     | 192 - 223   | - | 2^21 = 2,097,152   | Unicast (small networks)        |
| D     | 224 - 239   |                           |                    | Multicast                       |
| E     | 240 - 255   |                           |                    | Experimental                    |

latency 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
Read 1 MB sequentially from memory     250,000   ns      250 us
Round trip within same datacenter      500,000   ns      500 us
Read 1 MB sequentially from SSD*     1,000,000   ns    1,000 us    1 ms  ~1GB/sec SSD, 4X memory
Disk seek                           10,000,000   ns   10,000 us   10 ms  20x datacenter roundtrip
Read 1 MB sequentially from disk    20,000,000   ns   20,000 us   20 ms  80x memory, 20X SSD
Send packet CA->Netherlands->CA    150,000,000   ns  150,000 us  150 ms



list dynamic dependencies

linux bridge

a Linux kernel feature that connects two network segments (poor man’s router)

loose coupling

a system property and design strategy in which a system’s components have minimal knowledge of any other components. Two systems can be said to be loosely coupled when changes to one component generally don’t require changes to the other


(or serializing, or just encoding) converting non-bytes data into bytes

A program will typically build a complex data structure to hold the current program state. To transfer this data outside of the program’s own address space (e.g. to another application over the network) it needs to be serialized.

media speed (~2010)

| What              | Size       | Sequential Read Speed| Random Read Speed | Write Speed | Cost     |
| LTO-3 write speed |            |                      |                   |     80 MB/s | $0.06/GB |
| LTO-4 write speed |            |                      |                   |    120 MB/s | $0.05/GB |
| HD                | Terrabytes |             100 MB/s |            2 MB/s |             | $0.10/GB |
| SSD               | Gigabytes  |             250 MB/s |          250 MB/s |             | $3.00/GB |

Source: ULSAH, p. 210, 204

mutual authentication

process between a sender and a receiver authenticating each other’s identity to be sure who they are talking to. Mutual TLS (mTLS) is one well-known way to achieve mutually authenticated (and encrypted) traffic.




Set of characters indicating the end of a line:


in Go is an untyped identifier that represents the lack of a value for pointer types (e.g. *int) and types implemented with pointers (slices, maps, functions, channels, interfaces). Unlike NULL in C, nil is not another name for 0; you can’t convert it back and forth with a number.



The interruption of a computer process without its cooperation in order to perform another task.

Preemptive OS means that the rules governing which processes receive use of the CPU and for how long are determined by the kernel process scheduler rather than by the processes themselves.

Private Address Space

RFC 1918

| Class | Networks                      | Prefix     |
| A     | -  | 10/8       |
| B     | -  | 172.16/12  |
| C     | - | 192.168/16 |


# rfc 1918


Instructions (or commands, or statements) for a computer to execute. Cooking recipe or direction instructions are kinds of programs.

Executable file residing on disk in a directory. It is read into memory and is executed by the kernel as a result of one of the seven exec functions.


Java programs that run on the server on top of an application server platform.

stateless protocol

A communications protocol that treats each request as an independent transaction that is unrelated to any previous request (ex. HTTP).


DBES - decode bytes encode strings:

>>> raw_bytes = b'\xe6\x96\x80'
>>> raw_bytes.decode()   # DB
>>> utf_string = '斀'
>>> utf_string.encode()  # ES


(in Go) is a piece of storage containing a value


Exclusive or, the opposite of inclusive (normal) or.

Normal or allows both possibilities as well as either:

>>> True or True
>>> True or False
>>> False or True
>>> False or False

Exclusive or expression in Python:

>>> True != True
>>> True != False
>>> False != True
>>> False != False

Example of exclusive or in English: “You can have pizza or chicken” - you probably don’t mean you can have both.