241 lines
7.4 KiB
Markdown
241 lines
7.4 KiB
Markdown
Note that this is a Historical Document. It is a first attempt at
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figuring out basic design requirements.
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# 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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* 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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// Parser has access to all table metadata
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// Could also be called `SQLAbstractSyntaxTree`
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enum Operation {
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Select(TableName, ColumnSelection, Option<Condition>),
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Insert(TableName, Vec<(ColumnName, DbValue)>), // String because we don't yet know which type of value this is for sure
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Delete(TableName, Option<Condition>),
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// Update(...),
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}
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enum ColumnSelection {
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All,
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Columns(Vec<ColumnName>),
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}
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enum Condition = {
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// And(Condition, Condition),
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// Or(Condition, Condition),
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// Not(Condition),
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Eq(ColumnName, DbValue)
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// LessOrEqual(ColumnName, DbValue)
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// Less(ColumnName, DbValue)
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// StringCondition(StringCondition)
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}
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enum StringCondition {
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Prefix(ColumnName, String)
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Substring(ColumnName, String)
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}
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INSERT 123
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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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DbUUID(u32)
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}
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// We also need a type of db-types
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enum DbType {
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TString,
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TNumber,
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TId,
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}
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value_to_type(db_val: DbValue) -> DbType
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// table-metadata and data
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type TableName = String
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// Note that it is nice to split metadata from the data because
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// then you can give the metadata to the parser without giving it the data.
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struct TableMetaData {
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name: TableName,
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columns: Vec<(ColumnName, DbType, ColumnPosition)>
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}
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fn column(TableMetaData, ColumnName) -> ColumnPosition
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struct Table {
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meta: TableMetaData,
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rows: Rows // defined below
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indexes:
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BTree<ColumnName, Index>
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}
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type Tables = HashMap<TableName, Table>
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// We also need a function that for a given value computes its type (for validation)
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type ColumnName = String
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type ColumnPosition = u32
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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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type Rows =
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BTree<Id, 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, "Alice", 20.0 INTO persons;'
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Row ~> Vec<DbValue>
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e.g. Row ~> vec![DbUUID 1, DbSTring "Alice"]
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Vec<Vec<DbValue>>
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```
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* Interpreter
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```
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trait SqlConsumer {
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???
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}
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fn interpret<T: SqlConsumer>(operation: Operation, tables: &mut Tables, consumer: T) -> () {
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match operation {
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Select(table_name, column_selection, maybe_condition) => {
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let table: Table = ...
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select(table, column_selection, maybe_condition, consumer)
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},
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Insert(table_name, Vec<(ColumnName, DbValue)>) => {
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insert(table, ???)
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}
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Delete(table_name, maybe_condition) => {
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}
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}
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}
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response = interpret(...)
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knows_how_to_respond(response, client)
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enum Response {
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Selected(impl Iter<???>) // How to do this? Some reference to an iterator somehow... slice..?
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Inserted(???),
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Deleted(usize), // how many were deleted
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}
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fn select(table: Table, ColumnName
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```
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* 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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