Pekka Enberg beaccae664 Merge 'Create an automatic ephemeral index when a nested table scan would otherwise be selected' from Jussi Saurio
Closes #747
- Creates an automatic ephemeral (in-memory) index on the right-side
table of a join if otherwise a nested table scan would be selected.
- This behavior is not hardcoded; instead this PR introduces a (quite
dumb) cost estimator that naturally deincentivizes building ephemeral
indexes where they don't make sense (e.g. the outermost table). I will
probably build this estimator to be smarter in the future when working
on join reordering optimizations
### Example bytecode plans and runtimes (note that this is debug mode)
Example query with no persistent indexes to choose from. Without
ephemeral index it's a nested scan:
```sql
limbo> explain select * from t1 natural join t2;
addr  opcode             p1    p2    p3    p4             p5  comment
----  -----------------  ----  ----  ----  -------------  --  -------
0     Init               0     13    0                    0   Start at 13
1     OpenRead           0     2     0                    0   table=t1, root=2
2     OpenRead           1     3     0                    0   table=t2, root=3
3     Rewind             0     12    0                    0   Rewind t1
4       Rewind           1     11    0                    0   Rewind t2
5         Column         0     0     2                    0   r[2]=t1.a
6         Column         1     0     3                    0   r[3]=t2.a
7         Ne             2     3     10                   0   if r[2]!=r[3] goto 10
8         Column         0     0     1                    0   r[1]=t1.a
9         ResultRow      1     1     0                    0   output=r[1]
10      Next             1     5     0                    0
11    Next               0     4     0                    0
12    Halt               0     0     0                    0
13    Transaction        0     0     0                    0   write=false
14    Goto               0     1     0                    0

limbo> .timer on
limbo> select * from t1 natural join t2;
┌───┐
│ a │
├───┤
└───┘
Command stats:
----------------------------
total: 953 ms (this includes parsing/coloring of cli app)
```
Same query with autoindexing enabled:
```sql
limbo> explain select * from t1 natural join t2;
addr  opcode             p1    p2    p3    p4             p5  comment
----  -----------------  ----  ----  ----  -------------  --  -------
0     Init               0     22    0                    0   Start at 22
1     OpenRead           0     2     0                    0   table=t1, root=2
2     OpenRead           1     3     0                    0   table=t2, root=3
3     Rewind             0     21    0                    0   Rewind t1
4       Once             12    0     0                    0   goto 12 # execute block 5-11 only once, on subsequent iters jump straight to 12
5       OpenAutoindex    3     0     0                    0   cursor=3
6       Rewind           1     12    0                    0   Rewind t2 # open source table for ephemeral index
7         Column         1     0     2                    0   r[2]=t2.a
8         RowId          1     3     0                    0   r[3]=t2.rowid
9         MakeRecord     2     2     4                    0   r[4]=mkrec(r[2..3])
10        IdxInsert      3     4     2                    0   key=r[4] # insert stuff to ephemeral index
11      Next             1     7     0                    0
12      Column           0     0     5                    0   r[5]=t1.a
13      IsNull           5     20    0                    0   if (r[5]==NULL) goto 20
14      SeekGE           3     20    5                    0   key=[5..5] # perform seek on ephemeral index
15        IdxGT          3     20    5                    0   key=[5..5]
16        DeferredSeek   3     1     0                    0
17        Column         0     0     1                    0   r[1]=t1.a
18        ResultRow      1     1     0                    0   output=r[1]
19      Next             2     15    0                    0
20    Next               0     4     0                    0
21    Halt               0     0     0                    0
22    Transaction        0     0     0                    0   write=false
23    Goto               0     1     0                    0

limbo> .timer on
limbo> select * from t1 natural join t2;
┌───┐
│ a │
├───┤
└───┘
Command stats:
----------------------------
total: 220 ms (this includes parsing/coloring of cli app)
```

Closes #1356
2025-04-22 13:00:06 +03:00
2025-04-15 12:45:46 -03:00
2025-04-22 08:46:37 +02:00
2025-04-11 09:44:02 -03:00
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2025-04-14 16:52:13 -03:00
2025-03-29 14:46:11 +02:00
2025-03-25 14:17:31 +01:00
2025-04-22 08:46:37 +02:00
2025-01-14 18:37:26 +02:00
2025-04-12 17:47:16 -03:00
2025-04-15 12:45:46 -03:00
2025-04-16 15:23:02 +03:00
2025-04-16 15:21:48 +03:00
2025-04-21 23:05:01 -03:00
2025-01-30 18:24:19 -03:00
2025-03-23 20:29:55 -03:00
2024-05-07 16:33:44 -03:00
2025-04-15 12:51:43 -03:00
2025-03-30 18:58:33 +03:00
2025-04-22 09:46:16 +03:00
2024-07-12 13:07:34 -07:00
2024-07-12 12:38:56 -07:00
2025-04-15 12:45:46 -03:00
2025-04-22 12:11:23 +03:00
2025-04-15 12:45:46 -03:00

Limbo

Project Limbo

Limbo is a project to build the modern evolution of SQLite.

PyPI PyPI PyPI

Chat with developers on Discord


Features and Roadmap

Limbo is a work-in-progress, in-process OLTP database engine library written in Rust that has:

  • Asynchronous I/O support on Linux with io_uring
  • SQLite compatibility [doc] for SQL dialect, file formats, and the C API
  • Language bindings for JavaScript/WebAssembly, Rust, Go, Python, and Java
  • OS support for Linux, macOS, and Windows

In the future, we will be also working on:

  • Integrated vector search for embeddings and vector similarity.
  • BEGIN CONCURRENT for improved write throughput.
  • Improved schema management including better ALTER support and strict column types by default.

Getting Started

💻 Command Line
You can install the latest `limbo` release with:
curl --proto '=https' --tlsv1.2 -LsSf \
  https://github.com/tursodatabase/limbo/releases/latest/download/limbo_cli-installer.sh | sh

Then launch the shell to execute SQL statements:

Limbo
Enter ".help" for usage hints.
Connected to a transient in-memory database.
Use ".open FILENAME" to reopen on a persistent database
limbo> CREATE TABLE users (id INT PRIMARY KEY, username TEXT);
limbo> INSERT INTO users VALUES (1, 'alice');
limbo> INSERT INTO users VALUES (2, 'bob');
limbo> SELECT * FROM users;
1|alice
2|bob

You can also build and run the latest development version with:

cargo run
🦀 Rust
cargo add limbo

Example usage:

let db = Builder::new_local("sqlite.db").build().await?;
let conn = db.connect()?;

let res = conn.query("SELECT * FROM users", ()).await?;
JavaScript
npm i limbo-wasm

Example usage:

import { Database } from 'limbo-wasm';

const db = new Database('sqlite.db');
const stmt = db.prepare('SELECT * FROM users');
const users = stmt.all();
console.log(users);
🐍 Python
pip install pylimbo

Example usage:

import limbo

con = limbo.connect("sqlite.db")
cur = con.cursor()
res = cur.execute("SELECT * FROM users")
print(res.fetchone())
🐹 Go
  1. Clone the repository
  2. Build the library and set your LD_LIBRARY_PATH to include limbo's target directory
cargo build --package limbo-go
export LD_LIBRARY_PATH=/path/to/limbo/target/debug:$LD_LIBRARY_PATH
  1. Use the driver
go get github.com/tursodatabase/limbo
go install github.com/tursodatabase/limbo

Example usage:

import (
    "database/sql"
    _"github.com/tursodatabase/limbo"
)

conn, _ = sql.Open("sqlite3", "sqlite.db")
defer conn.Close()

stmt, _ := conn.Prepare("select * from users")
defer stmt.Close()

rows, _ = stmt.Query()
for rows.Next() {
    var id int
    var username string
    _ := rows.Scan(&id, &username)
    fmt.Printf("User: ID: %d, Username: %s\n", id, username)
}
Java

We integrated Limbo into JDBC. For detailed instructions on how to use Limbo with java, please refer to the README.md under bindings/java.

Contributing

We'd love to have you contribute to Limbo! Please check out the contribution guide to get started.

FAQ

How is Limbo different from Turso's libSQL?

Limbo is a project to build the modern evolution of SQLite in Rust, with a strong open contribution focus and features like native async support, vector search, and more. The libSQL project is also an attempt to evolve SQLite in a similar direction, but through a fork rather than a rewrite.

Rewriting SQLite in Rust started as an unassuming experiment, and due to its incredible success, replaces libSQL as our intended direction. At this point, libSQL is production ready, Limbo is not - although it is evolving rapidly. As the project starts to near production readiness, we plan to rename it to just "Turso". More details here.

Publications

  • Pekka Enberg, Sasu Tarkoma, Jon Crowcroft Ashwin Rao (2024). Serverless Runtime / Database Co-Design With Asynchronous I/O. In EdgeSys 24. [PDF]
  • Pekka Enberg, Sasu Tarkoma, and Ashwin Rao (2023). Towards Database and Serverless Runtime Co-Design. In CoNEXT-SW 23. [PDF] [Slides]

License

This project is licensed under the MIT license.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in Limbo by you, shall be licensed as MIT, without any additional terms or conditions.

Contributors

Thanks to all the contributors to Limbo!

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