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: 594.1115740190@sss.pgh.pa.us
(см: обсуждение, исходный текст)
Ответ на: Re: [GENERAL] "Hash index" vs. "b-tree index" (PostgreSQL  ("Jim C. Nasby")
Ответы: 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:
> What's the challange to making it adaptive, comming up with an algorithm
> that gives you the optimal bucket size (which I would think there's
> research on...) or allowing the index to accommodate different bucket
> sizes existing in the index at once? (Presumably you don't want to
> re-write the entire index every time it looks like a different bucket
> size would help.)

Exactly.  That's (a) expensive and (b) really hard to fit into the WAL
paradigm --- I think we could only handle it as a REINDEX.  So if it
were adaptive at all I think we'd have to support multiple bucket sizes
existing simultaneously in the index, and I do not see a good way to do
that.

Allowing a bucket size to be specified at CREATE INDEX doesn't seem out
of line though.  We'd have to think up a scheme for index-AM-specific
index parameters ...

            regards, tom lane


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