Jussi Saurio fe65d6e991 Merge 'Performance: hoist entire expressions out of hot loops if they are constant' from Jussi Saurio
## Problem:
- We have cases where we are evaluating expressions in a hot loop that
could only be evaluated once. For example: `CAST('2025-01-01' as
DATETIME)` -- the value of this never changes, so we should only run it
once.
- We have no robust way of doing this right now for entire _expressions_
-- the only existing facility we have is
`program.mark_last_insn_constant()`, which has no concept of how many
instructions translating a given _expression_ spends, and breaks very
easily for this reason.
## Main ideas of this PR:
- Add `expr.is_constant()` determining whether the expression is
compile-time constant. Tries to be conservative and not deem something
compile-time constant if there is no certainty.
- Whenever we think a compile-time constant expression is about to be
translated into bytecode in `translate_expr()`, start a so called
`constant span`, which means a range of instructions that are part of a
compile-time constant expression.
- At the end of translating the program, all `constant spans` are
hoisted outside of any table loops so they only get evaluated once.
- The target offsets of any jump instructions (e.g. `Goto`) are moved to
the correct place, taking into account all instructions whose offsets
were shifted due to moving the compile-time constant expressions around.
- An escape hatch wrapper `translate_expr_no_constant_opt()` is added
for cases where we should not hoist constants even if we otherwise
could. Right now the only example of this is cases where we are reusing
the same register(s) in multiple iterations of some kind of loop, e.g.
`VALUES(...)` or in the `coalesce()` function implementation.
## Performance effects
Here is an example of a modified/simplified TPC-H query where the
`CAST()` calls were previously run millions of times in a hot loop, but
now they are optimized out of the loop.
**BYTECODE PLAN BEFORE:**
```sql
limbo> explain select
        l_orderkey,
        3 as revenue,
        o_orderdate,
        o_shippriority
from
        lineitem,
        orders,
        customer
where
        c_mktsegment = 'FURNITURE'
        and c_custkey = o_custkey
        and l_orderkey = o_orderkey
        and o_orderdate < cast('1995-03-29' as datetime)
        and l_shipdate > cast('1995-03-29' as datetime);
addr  opcode             p1    p2    p3    p4             p5  comment
----  -----------------  ----  ----  ----  -------------  --  -------
0     Init               0     26    0                    0   Start at 26
1     OpenRead           0     10    0                    0   table=lineitem, root=10
2     OpenRead           1     9     0                    0   table=orders, root=9
3     OpenRead           2     8     0                    0   table=customer, root=8
4     Rewind             0     25    0                    0   Rewind lineitem
5       Column           0     10    5                    0   r[5]=lineitem.l_shipdate
6       String8          0     7     0     1995-03-29     0   r[7]='1995-03-29'
7       Function         0     7     6     cast           0   r[6]=func(r[7..8])  <-- CAST() executed millions of times
8       Le               5     6     24                   0   if r[5]<=r[6] goto 24
9       Column           0     0     9                    0   r[9]=lineitem.l_orderkey
10      SeekRowid        1     9     24                   0   if (r[9]!=orders.rowid) goto 24
11      Column           1     4     10                   0   r[10]=orders.o_orderdate
12      String8          0     12    0     1995-03-29     0   r[12]='1995-03-29'
13      Function         0     12    11    cast           0   r[11]=func(r[12..13])
14      Ge               10    11    24                   0   if r[10]>=r[11] goto 24
15      Column           1     1     14                   0   r[14]=orders.o_custkey
16      SeekRowid        2     14    24                   0   if (r[14]!=customer.rowid) goto 24
17      Column           2     6     15                   0   r[15]=customer.c_mktsegment
18      Ne               15    16    24                   0   if r[15]!=r[16] goto 24
19      Column           0     0     1                    0   r[1]=lineitem.l_orderkey
20      Integer          3     2     0                    0   r[2]=3
21      Column           1     4     3                    0   r[3]=orders.o_orderdate
22      Column           1     7     4                    0   r[4]=orders.o_shippriority
23      ResultRow        1     4     0                    0   output=r[1..4]
24    Next               0     5     0                    0
25    Halt               0     0     0                    0
26    Transaction        0     0     0                    0   write=false
27    String8            0     8     0     DATETIME       0   r[8]='DATETIME'
28    String8            0     13    0     DATETIME       0   r[13]='DATETIME'
29    String8            0     16    0     FURNITURE      0   r[16]='FURNITURE'
30    Goto               0     1     0
```
**BYTECODE PLAN AFTER**:
```sql
limbo> explain select
        l_orderkey,
        3 as revenue,
        o_orderdate,
        o_shippriority
from
        lineitem,
        orders,
        customer
where
        c_mktsegment = 'FURNITURE'
        and c_custkey = o_custkey
        and l_orderkey = o_orderkey
        and o_orderdate < cast('1995-03-29' as datetime)
        and l_shipdate > cast('1995-03-29' as datetime);
addr  opcode             p1    p2    p3    p4             p5  comment
----  -----------------  ----  ----  ----  -------------  --  -------
0     Init               0     21    0                    0   Start at 21
1     OpenRead           0     10    0                    0   table=lineitem, root=10
2     OpenRead           1     9     0                    0   table=orders, root=9
3     OpenRead           2     8     0                    0   table=customer, root=8
4     Rewind             0     20    0                    0   Rewind lineitem
5       Column           0     10    5                    0   r[5]=lineitem.l_shipdate
6       Le               5     6     19                   0   if r[5]<=r[6] goto 19
7       Column           0     0     9                    0   r[9]=lineitem.l_orderkey
8       SeekRowid        1     9     19                   0   if (r[9]!=orders.rowid) goto 19
9       Column           1     4     10                   0   r[10]=orders.o_orderdate
10      Ge               10    11    19                   0   if r[10]>=r[11] goto 19
11      Column           1     1     14                   0   r[14]=orders.o_custkey
12      SeekRowid        2     14    19                   0   if (r[14]!=customer.rowid) goto 19
13      Column           2     6     15                   0   r[15]=customer.c_mktsegment
14      Ne               15    16    19                   0   if r[15]!=r[16] goto 19
15      Column           0     0     1                    0   r[1]=lineitem.l_orderkey
16      Column           1     4     3                    0   r[3]=orders.o_orderdate
17      Column           1     7     4                    0   r[4]=orders.o_shippriority
18      ResultRow        1     4     0                    0   output=r[1..4]
19    Next               0     5     0                    0
20    Halt               0     0     0                    0
21    Transaction        0     0     0                    0   write=false
22    String8            0     7     0     1995-03-29     0   r[7]='1995-03-29'
23    String8            0     8     0     DATETIME       0   r[8]='DATETIME'
24    Function           1     7     6     cast           0   r[6]=func(r[7..8]) <-- CAST() executed twice
25    String8            0     12    0     1995-03-29     0   r[12]='1995-03-29'
26    String8            0     13    0     DATETIME       0   r[13]='DATETIME'
27    Function           1     12    11    cast           0   r[11]=func(r[12..13])
28    String8            0     16    0     FURNITURE      0   r[16]='FURNITURE'
29    Integer            3     2     0                    0   r[2]=3
30    Goto               0     1     0                    0
```
**EXECUTION RUNTIME BEFORE:**
```sql
limbo> select
        l_orderkey,
        3 as revenue,
        o_orderdate,
        o_shippriority
from
        lineitem,
        orders,
        customer
where
        c_mktsegment = 'FURNITURE'
        and c_custkey = o_custkey
        and l_orderkey = o_orderkey
        and o_orderdate < cast('1995-03-29' as datetime)
        and l_shipdate > cast('1995-03-29' as datetime);
┌────────────┬─────────┬─────────────┬────────────────┐
│ l_orderkey │ revenue │ o_orderdate │ o_shippriority │
├────────────┼─────────┼─────────────┼────────────────┤
└────────────┴─────────┴─────────────┴────────────────┘
Command stats:
----------------------------
total: 3.633396667 s (this includes parsing/coloring of cli app)
```
**EXECUTION RUNTIME AFTER:**
```sql
limbo> select
        l_orderkey,
        3 as revenue,
        o_orderdate,
        o_shippriority
from
        lineitem,
        orders,
        customer
where
        c_mktsegment = 'FURNITURE'
        and c_custkey = o_custkey
        and l_orderkey = o_orderkey
        and o_orderdate < cast('1995-03-29' as datetime)
        and l_shipdate > cast('1995-03-29' as datetime);
┌────────────┬─────────┬─────────────┬────────────────┐
│ l_orderkey │ revenue │ o_orderdate │ o_shippriority │
├────────────┼─────────┼─────────────┼────────────────┤
└────────────┴─────────┴─────────────┴────────────────┘
Command stats:
----------------------------
total: 2.0923475 s (this includes parsing/coloring of cli app)
````

Reviewed-by: Pere Diaz Bou <pere-altea@homail.com>

Closes #1359
2025-04-25 16:55:41 +03:00
2025-04-15 12:45:46 -03:00
2025-04-22 08:46:37 +02:00
2025-04-09 14:05:22 -04:00
2025-03-29 14:46:11 +02:00
2025-03-25 14:17:31 +01:00
2025-04-24 20:46:26 +03:00
2025-01-14 18:37:26 +02:00
2025-04-12 17:47:16 -03:00
2025-04-15 12:45:46 -03:00
2025-04-24 20:46:26 +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
2025-03-30 18:58:33 +03:00
2025-04-22 21:36:07 -04:00
2024-07-12 13:07:34 -07:00
2024-07-12 12:38:56 -07:00
2025-04-22 12:11:23 +03:00
2025-04-23 10:32:38 +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!

Description
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Tcl 6.6%
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