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From:Vyacheslav Akhmechet Date:May 15 2009 2:08am
Subject:Re: Handling of keypart_map in custom storage engine
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I see, this makes sense. Thanks!

On Thu, May 14, 2009 at 12:36 PM, MARK CALLAGHAN <mdcallag@stripped> wrote:
> On Thu, May 14, 2009 at 9:23 AM, Sergei Golubchik <serg@stripped> wrote:
>> Hi, MARK!
>>
>> On May 14, MARK CALLAGHAN wrote:
>>> On Thu, May 14, 2009 at 3:09 AM, Sergei Golubchik <serg@stripped>
> wrote:
>>> > On May 13, Vyacheslav Akhmechet wrote:
>>> >>
>>> >> Suppose a given key has two parts, A and B, and I build an index on
>>> >> this key (by combining A and B in lexicographic order, or a similar
>>> >> technique). Now, suppose index_read is called, and part A is
> missing
>>> >> from the key. In this case the index is essentially useless - I
> need
>>> >> to do a full table scan. I don't see how one could implement an
> index
>>> >> to get around this.
>>> >>
>>> >> Am I misunderstanding the purpose/semantics of keypart_map?
>>> >
>>> > No, you are not. Btree indexes, indeed, cannot support this feature.
>>> > Bitmap indexes, I presume, can.
>>>
>>> Btrees can and do support index scans in this case. Check out index
>>> skip scan in Oracle.
>>> http://www.google.com/search?q=index+skip+scan
>>
>> Yes, right.
>> In btree you can do an index scan, but it won't be a range as with a
>> prefix key.
>>
>> Thanks for correcting me.
>
> No, now I understand. In the context of calls to the index scan
> methods in handler.h, btree cannot support this. My statement ignored
> that context.
>
> But speaking about index skip scan and bitmap indexes, when do we get
> support for them? There is some support in the optimizer for index-or
> and index-and. Is there any chance that will be expanded to support
> more complex predicates and costs that make bitmap indexes
> interesting?
>
> --
> Mark Callaghan
> mdcallag@stripped
>
Thread
Handling of keypart_map in custom storage engineVyacheslav Akhmechet14 May
  • Re: Handling of keypart_map in custom storage engineSergei Golubchik14 May
    • Re: Handling of keypart_map in custom storage engineMARK CALLAGHAN14 May
      • Re: Handling of keypart_map in custom storage engineSergei Golubchik14 May
        • Re: Handling of keypart_map in custom storage engineMARK CALLAGHAN14 May
          • Re: Handling of keypart_map in custom storage engineVyacheslav Akhmechet15 May
          • Re: Handling of keypart_map in custom storage engineSergei Golubchik15 May
          • Re: Handling of keypart_map in custom storage engineMichael Widenius5 Jun