Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL

От: Tom Lane
Тема: Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL
Дата: ,
Msg-id: 20884.1115748420@sss.pgh.pa.us
(см: обсуждение, исходный текст)
Ответ на: Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  ("Jim C. Nasby")
Список: pgsql-performance

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"Hash index" vs. "b-tree index" (PostgreSQL 8.0)  (Ying Lu, )
 Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL 8.0)  (Neil Conway, )
  Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL 8.0)  (Christopher Petrilli, )
   Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  (Neil Conway, )
    Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  ("Jim C. Nasby", )
     Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  (Neil Conway, )
      Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  ("Jim C. Nasby", )
       Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  (Neil Conway, )
        Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  (Tom Lane, )
         Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  (Neil Conway, )
          Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  (Tom Lane, )
           Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  (Neil Conway, )
           Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  (Greg Stark, )
            Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  (Tom Lane, )
             Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  (Greg Stark, )
              Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  (Tom Lane, )
               Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  (Greg Stark, )
                Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  (Tom Lane, )
                 Federated PG servers -- Was: Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  (Mischa Sandberg, )
         Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  ("Jim C. Nasby", )
          Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  (Tom Lane, )
           Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  ("Jim C. Nasby", )
            Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  (Mischa Sandberg, )
        Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  ("Jim C. Nasby", )
         Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  (Tom Lane, )
         Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  (Mischa Sandberg, )
          Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  (Mark Lewis, )
          Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  (Tom Lane, )
           Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  (Mischa Sandberg, )
       Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  (Bruce Momjian, )
 Re: "Hash index" vs. "b-tree index" (PostgreSQL 8.0)  (David Roussel, )
 Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  (Tom Lane, )
  Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  (Neil Conway, )
 Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  (Greg Stark, )

"Jim C. Nasby" <> writes:
> Well, in a hash-join right now you normally end up feeding at least one
> side of the join with a seqscan. Wouldn't it speed things up
> considerably if you could look up hashes in the hash index instead?

That's called a "nestloop with inner index scan", not a hash join.

            regards, tom lane


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