From: | "Ansley, Michael" <Michael(dot)Ansley(at)intec(dot)co(dot)za> |
---|---|
To: | "'pgsql-general(at)hub(dot)org'" <pgsql-general(at)hub(dot)org> |
Subject: | RE: Data warehouse |
Date: | 1999-06-29 07:30:41 |
Message-ID: | 1BF7C7482189D211B03F00805F8527F70ECFB9@S-NATH-EXCH2 |
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Lists: | pgsql-general |
>> Herouth Maoz wrote:
>>
>> > Maybe I'm missing the point here, but it seems to me that if
>> > you simply use indices not as key definitions but as query
>> > accelerators (as in "index the living daylights out of"), then
>> > you may as well define a separate index on each and every
>> > field. Why do multiple-field indices in such a case?
>>
>> Why do multi-field indexes? Umm. How about to avoid doing a sequential
>> scan? If your query depends on multiple fields then once you've found
>> the set based on the first index you would have to sequential scan that
>> subset based on the second condition, unless you have a multi-field
>> index.
I suspect that Herouth was being a little facetious here. The bottom line
is that multi-column indices are necessary for indices other than the
primary
key, and shouldn't be limited to seven fields. However, in creating a
database
that can handle more than 7 fields in indices, there is some overhead built
in.
Thus, it should be something that the administrator can decide. There are
normally quite special reasons for wanting more than 7 fields in an index,
and
if you make it a pain to add the functionality to a PGSQL server, then
people will
rather design their dbs properly. However, in those cases where it is
absolutely
necessary, the functionality will at least be available.
And I daresay that this option will be used when compiling a server to
handle
warehouses.
MikeA
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