talkin' 'bout uuids

content/rnd/a_serialized_mystery/index.md

@@ -1,17 +1,71 @@
 +++
-title = "A Serialized Mystery, in One Part"
-slug = "serialized-mystery-one-part"
+title = "A One-Part Serialized Mystery"
+slug = "one-part-serialized-mystery"
 date = "2023-06-22"
 updated = "2023-06-22"
 [taxonomies]
-tags = ["software", "rnd", "proclamation", "upcsm"]
+tags = ["software", "rnd", "proclamation", "upscm"]
 [extra]
 toc = false
 +++
 
 # *Mise en Scene*
 
-Imagine, if you will, that you're a computer programmer.
+I recently spent a couple days moving from [one type of universally unique
+identifier](https://commons.apache.org/sandbox/commons-id/uuid.html) to a [different
+one](https://github.com/ulid/spec), for an in-progress [database-backed
+web-app](https://gitlab.com/nebkor/ww). The [initial
+work](https://gitlab.com/nebkor/ww/-/commit/be96100237da56313a583be6da3dc27a4371e29d#f69082f7433f159d627269b207abdaf2ad52b24c)
+didn't take very long, but debugging the [serialization and
+deserialization](https://en.wikipedia.org/wiki/Serialization) of the new IDs took another day and a half. So come with me on
+an exciting voyage of discovery, and [once again, learn from my
+folly](@/sundries/a-thoroughly-digital-artifact/index.md)!
+
+# Keys, primarily
+
+Most large distributed programs that people interact with daily via HTTP are, in essence, a fancy
+facade for some kind of database. Facebook? Database. Gmail? Database.
+
+![that's a database][thats_a_database]
+<center><span class="caption">wikipedia? that's a database.</span></center>
+
+In most databases, each entry ("row") has a field that acts as a [primary
+key](https://en.wikipedia.org/wiki/Primary_key), used to uniquely identify that row inside the table
+it's in. Since databases typically contain multiple tables, and primary keys have to be unique only
+within their own table, you could just use a simple integer that's automatically incremented every
+time you add a new record, and in many databases, if you create a table without specifying a primary
+key, they will [automatically and implicitly use a
+mechanism](https://www.sqlite.org/lang_createtable.html#rowid) like that.
+
+This is often totally fine! If you only ever have one copy of the database, and never have to worry
+about inserting rows from a different instance of the database, then you can just use those simple
+values and move on your merry way.
+
+However, if you ever think you might want to have multiple instances of your database running, and
+want to make sure they're eventually consistent with each other, then you might want to use a
+fancier identifier for your primary keys, to avoid collisions between primary keys.
+
+## UUIDs
+
+One very common type for these is called a
+[UUIDv4](https://datatracker.ietf.org/doc/html/rfc4122#page-14). These are 128-bit random
+numbers[^uuidv4_random], and when turned into a string, usually look something like
+`1c20104f-e04f-409e-9ad3-94455e5f4fea`; this is called the "hyphenated" form, for fairly obvious
+reasons. Although sometimes they're stored in a DB in that form directly, that's using 36 bytes to
+store 16 bytes' worth of data, which is more than twice as many bytes than necessary. And if you're
+a programmer, this sort of conspicous waste is unconscionsable.
+
+You can cut that to 32 bytes by just dropping the dashes, but then that's still twice as many bytes
+as the actual data requires. If you never have to actually display the ID inside the database, then
+the simplest thing to do is just store it as a blob of 16 bytes[^blob-of-bytes]. Finally, optimal
+representation and efficiency!
+
+## Indexes?
+
+
+
+Imagine, if you will, that you're a computer programmer. One common trait among such creatures is a
+desire to be "efficient".
 
  - programmers like efficiency
  - databases have primary keys and keep indices
@@ -23,3 +77,10 @@ Imagine, if you will, that you're a computer programmer.
 # First steps
 
 ## A puzzling failure
+
+----
+
+[^uuidv4_random]: Technically, most v4 UUIDs have only 122 random bits, as six out of 128 are
+reserved for version metadata.
+
+[thats_a_database]: ./thats_a_database.png "that's a database"