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.