Notes on CAS and git.

c-declarations
Joshua Potter 2024-02-29 08:52:05 -07:00
parent 4ad55dc8bf
commit 2a7400a255
10 changed files with 326 additions and 13 deletions

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@ -89,7 +89,7 @@
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@ -122,7 +122,7 @@
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@ -190,7 +190,7 @@
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}, },
"fields_dict": { "fields_dict": {
"Basic": [ "Basic": [

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---
title: "2024-02-29"
---
- [x] Anki Flashcards
- [x] KoL
- [ ] Sheet Music (10 min.)
- [x] Go (1 Life & Death Problem)
- [ ] Korean (Read 1 Story)
- [ ] Interview Prep (1 Practice Problem)
- [ ] Log Work Hours (Max 3 hours)
* 101weiqi (serial numbers)
* Q-349924
* Q-99982
* Q-285489
* Q-85874
* Q-265576
* Q-11420
* TODO
* Watch database courses and read

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@ -5,10 +5,10 @@ title: "2024-02-28"
- [x] Anki Flashcards - [x] Anki Flashcards
- [x] KoL - [x] KoL
- [ ] Sheet Music (10 min.) - [ ] Sheet Music (10 min.)
- [ ] Go (1 Life & Death Problem) - [x] Go (1 Life & Death Problem)
- [ ] Korean (Read 1 Story) - [ ] Korean (Read 1 Story)
- [ ] Interview Prep (1 Practice Problem) - [ ] Interview Prep (1 Practice Problem)
- [ ] Log Work Hours (Max 3 hours) - [x] Log Work Hours (Max 3 hours)
* 101weiqi (serial numbers) * 101weiqi (serial numbers)
* Q-314990 * Q-314990
@ -17,3 +17,5 @@ title: "2024-02-28"
* Q-51685 * Q-51685
* Q-11821 * Q-11821
* Q-5014 * Q-5014
* Add notes on `SIGABRT`.
* First pass on "Git Internals" in "Pro Git".

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%%ANKI %%ANKI
Basic Basic
Which hexadecimal digits have a leading `1` bit? Which hexadecimal digits encode binary with a leading `1` bit?
Back: `8` through `F` Back: `8` through `F`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016. Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: binary::hex Tags: binary::hex
@ -285,7 +285,7 @@ END%%
%%ANKI %%ANKI
Basic Basic
Which hexadecimal digits have a leading `0` bit? Which hexadecimal digits encode binary with a leading `0` bit?
Back: `0` through `7` Back: `0` through `7`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016. Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: binary::hex Tags: binary::hex

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%%ANKI %%ANKI
Basic Basic
*Why* is it $UMax = 2 \cdot TMax + 1$? Provide a combinatorial explanation on why $UMax$ equals $2 \cdot TMax + 1$.
Back: All bit strings representing negative numbers in two's-complement are positive in unsigned encoding. Back: There is one more negative number than positive numbers represented in two's-complement.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016. Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1708613447880--> <!--ID: 1708613447880-->
END%% END%%

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---
title: Content-Addressable Storage
TARGET DECK: Obsidian::STEM
FILE TAGS: fs::cas
tags:
- cas
- fs
---
## Overview
CAS (**c**ontent-**a**ddressed **s**torage) refers to storage that allows retrieval based on content (as opposed to name or location). Usually the contents of a file are passed through a cryptographic hash function to generate a key that can be used for subsequent retrieval.
%%ANKI
Basic
What is content-addressed storage?
Back: A method for storing information such that it can be retrieved based on its content.
Reference: “Content-Addressable Storage,” in _Wikipedia_, February 27, 2024, [https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681](https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681).
<!--ID: 1709177255543-->
END%%
%%ANKI
Basic
What is considered the "opposite" of content-addressed storage?
Back: Location-addressed storage.
Reference: “Content-Addressable Storage,” in _Wikipedia_, February 27, 2024, [https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681](https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681).
<!--ID: 1709177255547-->
END%%
%%ANKI
Basic
What is CAS an acronym for?
Back: **C**ontent-**a**ddressed **s**torage.
Reference: “Content-Addressable Storage,” in _Wikipedia_, February 27, 2024, [https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681](https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681).
<!--ID: 1709177255550-->
END%%
%%ANKI
Cloze
{1:Content}-addressed is to {2:URNs} whereas {2:location}-addressed is to {1:URLs}.
Reference: “Content-Addressable Storage,” in _Wikipedia_, February 27, 2024, [https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681](https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681).
<!--ID: 1709177255553-->
END%%
%%ANKI
Basic
Interpreted as a key-value store, what is a "key" in a CAS system?
Back: The digest produced when running content through a cryptographic hash function.
Reference: “Content-Addressable Storage,” in _Wikipedia_, February 27, 2024, [https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681](https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681).
<!--ID: 1709177255556-->
END%%
%%ANKI
Basic
Interpreted as a key-value store, what is a "value" in a CAS system?
Back: The actual content being stored.
Reference: “Content-Addressable Storage,” in _Wikipedia_, February 27, 2024, [https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681](https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681).
<!--ID: 1709177255559-->
END%%
%%ANKI
Basic
In the context of CAS, what is a "content address"?
Back: A digest produced when running content through a cryptographic hash function.
Reference: “Content-Addressable Storage,” in _Wikipedia_, February 27, 2024, [https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681](https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681).
<!--ID: 1709177255562-->
END%%
%%ANKI
Cloze
Content addresses are an alternative to {location} addresses found in traditional filesystems.
Reference: “Content-Addressable Storage,” in _Wikipedia_, February 27, 2024, [https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681](https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681).
<!--ID: 1709177255565-->
END%%
%%ANKI
Basic
Why are CAS systems sometimes called "fixed content storage"?
Back: CAS is normally used for files that are not frequently edited.
Reference: “Content-Addressable Storage,” in _Wikipedia_, February 27, 2024, [https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681](https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681).
<!--ID: 1709177255567-->
END%%
%%ANKI
Basic
How is it CAS systems ensure file uniqueness?
Back: An attempt to store an already stored file will generate the same key as before.
Reference: “Content-Addressable Storage,” in _Wikipedia_, February 27, 2024, [https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681](https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681).
<!--ID: 1709177255570-->
END%%
%%ANKI
Basic
How is it CAS systems ensure file's remain unchanged?
Back: A file's key will always be the same provided the content has not changed.
Reference: “Content-Addressable Storage,” in _Wikipedia_, February 27, 2024, [https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681](https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681).
<!--ID: 1709177255573-->
END%%
## References
* “Content-Addressable Storage,” in _Wikipedia_, February 27, 2024, [https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681](https://en.wikipedia.org/w/index.php?title=Content-addressable_storage&oldid=1210669681).
* Scott Chacon, _Pro Git_, Second edition, The Experts Voice in Software Development (New York, NY: Apress, 2014).

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---
title: Filesystems
---

3
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---
title: Git
---

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---
title: Objects
TARGET DECK: Obsidian::STEM
FILE TAGS: fs::cas git
tags:
- cas
- fs
- git
---
## Overview
%%ANKI
Basic
What cryptographic hash function does git use internally?
Back: SHA-1
Reference: Scott Chacon, *Pro Git*, Second edition, The Experts Voice in Software Development (New York, NY: Apress, 2014).
<!--ID: 1709177255577-->
END%%
%%ANKI
Basic
How many bytes make up a SHA-1 digest?
Back: 20
Reference: Scott Chacon, *Pro Git*, Second edition, The Experts Voice in Software Development (New York, NY: Apress, 2014).
<!--ID: 1709177255580-->
END%%
%%ANKI
Basic
How many hexadecimal digits make up a SHA-1 digest?
Back: 40
Reference: Scott Chacon, *Pro Git*, Second edition, The Experts Voice in Software Development (New York, NY: Apress, 2014).
<!--ID: 1709177255584-->
END%%
%%ANKI
Basic
How is a SHA-1 digest typically represented?
Back: As a string of 40 hexadecimal digits.
Reference: Scott Chacon, *Pro Git*, Second edition, The Experts Voice in Software Development (New York, NY: Apress, 2014).
<!--ID: 1709177255589-->
END%%
%%ANKI
Basic
What is "oid" an acronym for?
Back: **O**bject **id**.
Reference: Scott Chacon, *Pro Git*, Second edition, The Experts Voice in Software Development (New York, NY: Apress, 2014).
<!--ID: 1709177255594-->
END%%
%%ANKI
Basic
What *is* an object id?
Back: The digest produced when hashing/storing content.
Reference: Scott Chacon, *Pro Git*, Second edition, The Experts Voice in Software Development (New York, NY: Apress, 2014).
<!--ID: 1709177255599-->
END%%
%%ANKI
Basic
What does it mean for git to be a content-addressed storage system?
Back: Keys generated from hashing content are used to later retrieve said content.
Reference: Scott Chacon, *Pro Git*, Second edition, The Experts Voice in Software Development (New York, NY: Apress, 2014).
Tags: fs::cas
<!--ID: 1709177255603-->
END%%
%%ANKI
Cloze
Interpreted as a key-value store, {oids} are to keys as {objects} are to values.
Reference: Scott Chacon, *Pro Git*, Second edition, The Experts Voice in Software Development (New York, NY: Apress, 2014).
Tags: fs::cas
<!--ID: 1709177255607-->
END%%
%%ANKI
Basic
Why prefer term "oid" over e.g. "SHA-1 digest" or similar?
Back: Git is transitioning to the use of other cryptographic hash functions.
Reference: Scott Chacon, *Pro Git*, Second edition, The Experts Voice in Software Development (New York, NY: Apress, 2014).
<!--ID: 1709177255612-->
END%%
%%ANKI
Basic
What is a "porcelain" command?
Back: A user-friendly command.
Reference: Scott Chacon, *Pro Git*, Second edition, The Experts Voice in Software Development (New York, NY: Apress, 2014).
<!--ID: 1709177255618-->
END%%
%%ANKI
Basic
What is a "plumbing" command?
Back: A lower-level command.
Reference: Scott Chacon, *Pro Git*, Second edition, The Experts Voice in Software Development (New York, NY: Apress, 2014).
<!--ID: 1709177255622-->
END%%
%%ANKI
Cloze
{Porcelain} commands are more user-friendly than {plumbing} commands.
Reference: Scott Chacon, *Pro Git*, Second edition, The Experts Voice in Software Development (New York, NY: Apress, 2014).
<!--ID: 1709177255627-->
END%%
%%ANKI
Basic
What plumbing subcommand is used to generate an oid?
Back: `hash-object`
Reference: Scott Chacon, *Pro Git*, Second edition, The Experts Voice in Software Development (New York, NY: Apress, 2014).
<!--ID: 1709177255632-->
END%%
%%ANKI
Basic
The `hash-object` subcommand optionally stores the resulting object in what directory?
Back: `.git/objects`
Reference: Scott Chacon, *Pro Git*, Second edition, The Experts Voice in Software Development (New York, NY: Apress, 2014).
<!--ID: 1709177255637-->
END%%
%%ANKI
Cloze
The {object database} refers to the {`.git/objects`} directory.
Reference: Scott Chacon, *Pro Git*, Second edition, The Experts Voice in Software Development (New York, NY: Apress, 2014).
<!--ID: 1709177255644-->
END%%
%%ANKI
Basic
What does the `hash-object` subcommand return?
Back: The computed object id.
Reference: Scott Chacon, *Pro Git*, Second edition, The Experts Voice in Software Development (New York, NY: Apress, 2014).
<!--ID: 1709177255651-->
END%%
%%ANKI
Basic
What optional functionality does the `hash-object` subcommand support?
Back: It can write an object into the object database.
Reference: Scott Chacon, *Pro Git*, Second edition, The Experts Voice in Software Development (New York, NY: Apress, 2014).
<!--ID: 1709177255659-->
END%%
%%ANKI
Basic
What flag lets the `hash-object` subcommand write to the object database?
Back: `-w`
Reference: Scott Chacon, *Pro Git*, Second edition, The Experts Voice in Software Development (New York, NY: Apress, 2014).
<!--ID: 1709177255664-->
END%%
%%ANKI
Basic
Where does object e.g. `d670460b4b4aece5915caf5c68d12f560a9fe3e4` live in the object database?
Back: At `.git/objects/d6/70460b4b4aece5915caf5c68d12f560a9fe3e4`.
Reference: Scott Chacon, *Pro Git*, Second edition, The Experts Voice in Software Development (New York, NY: Apress, 2014).
<!--ID: 1709177255668-->
END%%
%%ANKI
Basic
What regular files exist in the object database after `git init`?
Back: None.
Reference: Scott Chacon, *Pro Git*, Second edition, The Experts Voice in Software Development (New York, NY: Apress, 2014).
<!--ID: 1709177255672-->
END%%
## References
* Scott Chacon, *Pro Git*, Second edition, The Experts Voice in Software Development (New York, NY: Apress, 2014).

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%%ANKI %%ANKI
Basic Basic
How do define $s'$ such that $s(E_e^x) = s'(E)$? How do you define $s'$ such that $s(E_e^x) = s'(E)$?
Back: $s' = (s; x{:}s(e))$. Back: $s' = (s; x{:}s(e))$.
Reference: Gries, David. *The Science of Programming*. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981. Reference: Gries, David. *The Science of Programming*. Texts and Monographs in Computer Science. New York: Springer-Verlag, 1981.
<!--ID: 1707939006292--> <!--ID: 1707939006292-->