Chain Hashing

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От Jian He
Тема Chain Hashing
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Msg-id CAMV54g1GuB7Bqeq=iitVR5+NM23w-_4PrXaQV64ot3ikM_OzbA@mail.gmail.com
обсуждение исходный текст
Ответы Re: Chain Hashing  (Thomas Munro <thomas.munro@gmail.com>)
Список pgsql-general

Been following YouTube to study about Database Hash Join.  https://www.youtube.com/watch?v=J0nbgXIarhc
 HASH TABLE 
Design Decision
 #1: Hash Function → How to map a large key space into a smaller domain. → Trade-off between being fast vs. collision rate. Design Decision 
#2: Hashing Scheme → How to handle key collisions after hashing. → Trade-off between allocating a large hash table vs. additional instructions to find/insert keys.

Now I have some idea about the Hash function, but the math part I have no idea. 
Hash Scheme is for handling collisions. Collision means that different input keys will have some output hash bits.

The following part is about the Chain Hashing.  
  Maintain a linked list of buckets for each slot in the hash table. 
Resolve collisions by placing all elements with the same hash key into the same bucket. 
→ To determine whether an element is present, hash to its bucket and scan for it.
 → Insertions and deletions are generalizations of lookups.  
 
   I still don't get it. Stackoverflow seems don't have good answers yet. So I come here, asking.... 

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