Module key

This module contains implementation for hash key serialization for hash-agg, hash-join, and perhaps other hash-based operators.

There may be multiple columns in one row being combined and encoded into one single hash key. For example, SELECT sum(t.a) FROM t GROUP BY t.b, t.c, the hash keys are encoded from both t.b and t.c. If t.b="abc" and t.c=1, the hashkey may be encoded in certain format of ("abc", 1).

Macros

impl_memcmp_encoding_hash_key_serde 🔒

impl_value_encoding_hash_key_serde 🔒

Structs

HashCode

A wrapper for u64 hash result. Generic over the hasher.

HeapNullBitmap

Null bitmap on heap. We use this for the edge case where group key sizes are larger than 64. This is because group key null bits cannot fit into a u64 on the stack if they exceed 64 bits. NOTE(kwannoel): This is not really optimized as it is an edge case.

PrecomputedBuildHasher

PrecomputedHasher

A special hasher designed for HashKey, which stores a hash key from HashKey::hash() and outputs it on finish().

StackNullBitmap

Null Bitmap on stack. This is specialized for the common case where group keys (<= 64).

Statics

MAX_GROUP_KEYS_ON_STACK

This is determined by the stack based data structure we use, StackNullBitmap, which can store 64 bits at most.

Traits

HashKeyDe

The deserialization counterpart of HashKeySer.

HashKeySer

Extension of scalars to be serialized into hash keys.

NullBitmap

We use a trait for NullBitmap so we can parameterize structs on it. This is because NullBitmap is used often, and we want it to occupy the minimal stack space.

Type Aliases

Crc32HashCode

Hash code from the Crc32 hasher. Used for hash-shuffle exchange.

XxHash64HashCode

Hash code from the XxHash64 hasher. Used for in-memory hash map cache.