Module hash_table 

Optimized hash table for join operations.

This module provides a specialized hash table designed for the build phase of hash joins. Key optimizations:

1. Pre-allocated: Sized upfront based on build side cardinality
2. Cache-efficient: Linear probing within cache lines
3. Zero-allocation probe: Iterator returns indices without allocation
4. Full hash stored: Quick rejection without row access

Memory Layout

JoinHashTable
├── bucket_heads: Vec<i32>    [bucket_count]     // First entry index per bucket
├── entries: Vec<HashEntry>   [row_count]        // One per build row
└── bucket_mask: u64                             // For fast modulo

HashEntry (16 bytes, cache-aligned)
├── hash: u64     // Full hash for quick rejection
├── row_idx: u32  // Index into build rows
└── next: u32     // Next in chain (EMPTY = end)

Structs

JoinHashState

Immutable build-side state shared by every probe consumer of one physical JOIN edge.

JoinHashTable

Optimized hash table for join operations.

ProbeCursor

Borrow-free position in one hash bucket chain.

ProbeIter

Zero-allocation iterator over probe results.

Traits

JoinHashObserver

Minimal sink used while a JOIN hash table and a probe accelerator are populated in one pass. The optimizer owns the accelerator; the physical hash foundation depends only on this lifecycle-neutral contract.

Functions

hash_keys_with

Hash values at given indices using a get function.

hash_row_keys

Hash row key columns into a single u64.

verify_key_equality

Verify that two rows have equal key values.