Struct QueryArena 

pub struct QueryArena { /* private fields */ }

Arena allocator for query-scoped allocations

Uses a bump-pointer strategy to allocate from a pre-allocated buffer. All allocations are freed when the arena is reset or dropped.

Example

use vibesql_executor::memory::QueryArena;
use std::mem::MaybeUninit;

let arena = QueryArena::with_capacity(1024);

// Allocate a value
let x = arena.alloc(42i64);
assert_eq!(*x, 42);

// Allocate a slice (returns uninitialized memory)
let slice = arena.alloc_slice::<i32>(10);
for i in 0..10 {
    slice[i] = MaybeUninit::new(i as i32);
}

Implementations

impl QueryArena

pub const DEFAULT_CAPACITY: usize = 10_485_760usize

Default arena size: 10MB

Based on TPC-H Q6 analysis:

• 60K rows × 16 columns = 960K SqlValues
• Intermediate results: ~2MB
• Expression temporaries: ~1MB
• Safety margin: 7MB

pub fn with_capacity(bytes: usize) -> Self

Create a new arena with the specified capacity in bytes

Arguments

• bytes - Number of bytes to pre-allocate

Example

use vibesql_executor::memory::QueryArena;

// 1MB arena
let arena = QueryArena::with_capacity(1024 * 1024);

pub fn new() -> Self

Create a new arena with the default capacity (10MB)

Example

use vibesql_executor::memory::QueryArena;

let arena = QueryArena::new();

pub fn alloc<T>(&self, value: T) -> &T

Allocate a value in the arena

Returns a reference to the allocated value with lifetime tied to the arena.

Performance

Allocation overhead: ~1ns (vs ~100ns for heap allocation)

Panics

Panics if the arena is out of space. Use try_alloc for fallible allocation.

Example

use vibesql_executor::memory::QueryArena;

let arena = QueryArena::new();
let x = arena.alloc(42i64);
let y = arena.alloc(3.5f64);

assert_eq!(*x, 42);
assert_eq!(*y, 3.5);

pub fn alloc_slice<T>(&self, len: usize) -> &mut [MaybeUninit<T>]

Allocate a slice in the arena

Returns a mutable slice of MaybeUninit<T> with the specified length. Caller must initialize elements before assuming them to be initialized.

Using MaybeUninit ensures memory safety - uninitialized memory cannot be accidentally read or dropped, preventing undefined behavior.

Performance

Allocation overhead: ~1ns + negligible bounds check

Panics

Panics if the arena is out of space.

Example

use vibesql_executor::memory::QueryArena;
use std::mem::MaybeUninit;

let arena = QueryArena::new();
let slice = arena.alloc_slice::<i32>(100);

// Initialize the slice
for i in 0..100 {
    slice[i] = MaybeUninit::new(i as i32);
}

// SAFETY: All elements have been initialized above
let initialized_slice = unsafe {
    std::slice::from_raw_parts(
        slice.as_ptr() as *const i32,
        slice.len()
    )
};
assert_eq!(initialized_slice[50], 50);

pub fn try_alloc<T>(&self, value: T) -> Option<&T>

Try to allocate a value in the arena

Returns None if the arena is out of space.

Example

use vibesql_executor::memory::QueryArena;

let arena = QueryArena::with_capacity(64);

// This succeeds
assert!(arena.try_alloc(42i64).is_some());

// Eventually this fails (arena full)
let mut count = 0;
while arena.try_alloc(count).is_some() {
    count += 1;
}

pub fn reset(&mut self)

Reset the arena, allowing it to be reused

This doesn’t deallocate the buffer, just resets the bump pointer. All previously allocated values are invalidated.

Example

use vibesql_executor::memory::QueryArena;

let mut arena = QueryArena::new();

// Allocate some values (i64 = 8 bytes)
let x = arena.alloc(42i64);
assert_eq!(arena.used_bytes(), 8);

// Reset and reuse
arena.reset();
assert_eq!(arena.used_bytes(), 0);

// Can allocate again
let y = arena.alloc(100i64);

pub fn used_bytes(&self) -> usize

Get the number of bytes used in this arena

Example

use vibesql_executor::memory::QueryArena;

let arena = QueryArena::new();

arena.alloc(42i64); // 8 bytes
arena.alloc(3.5f64); // 8 bytes

assert_eq!(arena.used_bytes(), 16);

pub fn capacity_bytes(&self) -> usize

Get the total capacity of this arena in bytes

Example

use vibesql_executor::memory::QueryArena;

let arena = QueryArena::with_capacity(1024);
assert_eq!(arena.capacity_bytes(), 1024);

pub fn remaining_bytes(&self) -> usize

Get the number of bytes remaining in this arena

Example

use vibesql_executor::memory::QueryArena;

let arena = QueryArena::with_capacity(1024);
arena.alloc(42i64); // 8 bytes

assert_eq!(arena.remaining_bytes(), 1024 - 8);

Trait Implementations

impl Default for QueryArena

fn default() -> Self

Returns the “default value” for a type.