131 lines
5.1 KiB
Markdown
131 lines
5.1 KiB
Markdown
# MiniSQL
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## Official Description
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MiniSQL server
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Create a simple SQL server that supports SELECT (including column selection), INSERT and DELETE.
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The SELECT and DELETE statements support a WHERE clause with a single column.
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It is also possible to create indexes (hashes).
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The database works with persistent storage - it can be turned off and on without data loss.
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Create an interface to the database to work - either CLI or desktop application.
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## Resources
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### DB internals
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* [CMU intro to Database Systems](https://www.youtube.com/playlist?list=PLSE8ODhjZXjaKScG3l0nuOiDTTqpfnWFf)
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* Tutorial on sqlite clone in C: [Let's build a Simple Database. How Does a Database work?](https://cstack.github.io/db_tutorial/).
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* [sqlite opcodes](https://www.sqlite.org/opcode.html)
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### Parsing
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Parser Combinator libraries
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* [nom](https://github.com/rust-bakery/nom)
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* [parser_combinators](https://docs.rs/parser-combinators/latest/parser_combinators/)
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### TCP socket programming
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* See [simple http server](https://youtu.be/hzSsOV2F7-s) implementation with tcp sockets
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## Scope
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* Primarily in-memory db.
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* Occasionally will save its state on to the disk.
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* Almost non-existent concurrency control?
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* Inspiration from SQLite, but not the server part. For the server part take a look at Postgres.
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* Can create custom column indexes.
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* What about Joins?
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* What about composite queries (i.e. instead of a table name in a select expression we include another select expression)?
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# Building a Minimal Viable Product (MVP)
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Possible usage:
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* You start the db server with
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```./minisql server start --db path/to/db/my-db.db --port 1433```
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which will store the database as a file `path/to/db/my-db.db` and open a TCP server on port `1433`
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* Then on possibly a different machine you run `./minisql client connect server_ip_address:6666` to start a client. This will open a REPL with which you can send queries/db management commands
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* TODO: We should also consider writing a rust library that allows you to spin up a client that connects to the server.
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How would the interface look like?
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```
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use mysql::{DB, DBConnection}
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let maybe_conn: Result<DBConnection> = DB.connect({
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port: 1433,
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db_name: "db-name",
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username: "bojack",
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password: "12345"}
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): Result<DBConnection> ?;
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let conn: DBConnection = maybe_conn?;
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// then we can execute queries
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conn.perform("SELECT id, name, title, salary FROM employees"): ???
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```
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* Then with the client cli we can request creation of tables/insertion of data etc
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```
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> CREATE TABLE persons(id u32 PRIMARY KEY, name String, salary Float)
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> INSERT 1, "Alice", 20.0 INTO persons;
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> INSERT 2, "Bob", 30 INTO persons;
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> INSERT 3, "Claire", 15 INTO persons;
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```
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* How should the SQL AST look like? For example when server parses `SELECT id, name FROM persons;`,
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how will the parsing output look like?
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Consider something like
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```
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// Could also be called `SQLAbstractSyntaxTree`
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enum Operations {
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Select(Vector<FieldName>, TableName),
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Update(...)
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}
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```
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* We also have to write an interpreter for these operations. How will the db-state be represented in memory?
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For example how can we implement a table?
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```
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// Not exactly efficient, but how could we do better?
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enum DbValue {
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DbString(String),
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DbNumber(Float),
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DbByte(u8),
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DbUUID(u32)
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}
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type ColumnName = String
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// The below type is a type of a table row
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type Row = HashMap<ColumnName, DbValue>
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// Or you know... some appropriate Dictionary Type
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HashMap::make![("id", 1), ("name", "Alice"), ("salary", 20.0)] : Row
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// possible optimization: have a mapping
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// column names ~> indexes
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// so that we could represent rows as
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type Row = Vec<DbValue>
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// How to represent a table?
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table : HashMap<Id, Row>
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Vec<(Id, Row)>.
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// suppose the row corresponds to 'INSERT 1, "Yura", 20.0 INTO persons;'
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Row ~> Vec<DbValue>
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e.g. Row ~> vec![DbUUID 1, DbSTring "Yura"]
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Vec<Vec<DbValue>>
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```
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* TODO: Consider streaming the response to the client and not just dumping 10K rows at once.
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## Server
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1. **Client input parsing/validation** string input from the client to Abstract Syntax Tree (AST) that represents SQL query
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2. **Code gen** (Not necessary for MVP) from SQL AST generating bytecode for a more low-level VM.
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3. **VM** (Not necessary for MVP) implement low-level VM that governs the in-memory db.
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4. **Persistence** Serialize in-memory db state to a file. What format should it have? At first perhaps just a dumb json serialization? You also have to implement the deserialization.
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5. **Client response** Stream selected rows/status/error messages back to the client. What should the protocol look like? Take a look at [Tabular Data Stream](https://en.wikipedia.org/wiki/Tabular_Data_Stream) or just respond with json.
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6. **Concurrency control** Consider what happens when two clients simultaneously wish to updat ethe same row. There has to be some minimal mutual exclusion/locking.
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7. **Security** Should we worry about secure communication over TCP?
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## Client
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1. **Opens TCP connection to server**
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2. **REPL** has to provide a basic REPL interface
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3. **Server Response decoder** Has to properly format the data/status/error messages from the server. Does the client have to parse the queries? Or is that only the server's responsibility?
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