Re: plans for bitmap indexes?
От | Chris Browne |
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Тема | Re: plans for bitmap indexes? |
Дата | |
Msg-id | 604ql3x0g7.fsf@dba2.int.libertyrms.com обсуждение исходный текст |
Ответ на | Re: plans for bitmap indexes? ("Dave Page" <dpage@vale-housing.co.uk>) |
Ответы |
Re: plans for bitmap indexes?
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Список | pgsql-hackers |
yann-postgresql@spline.de (Yann Michel) writes: > On Fri, Oct 08, 2004 at 10:09:18AM +0100, Dave Page wrote: >> I think what Reini was asking was why do you think you need bitmap >> indexes as opposed to any existing type? > > due to I'm developing a datawarehousing application we have lots of > fact-data in our central fact-table. As I know how to improve > performance on Oracle based datawarehouses, I'm used to add bitmap > indexes for atributes having only a few distinct values. So I was > looking for any comparable indexing technology but didn't find any > so far. The most nearly comparable thing is be the notion of "partial indexes," where, supposing you had 60 region codes (e.g. - 50 US states, 10 Canadian provinces), you might set up indices thus: TABLE=my_table FIELD=stateprov FILE=$HOME/regionlist.txt for region in `cat $FILE`; do query="create index ${TABLE}_partial_on_${region} on $TABLE($FIELD) where $FIELD = '$region';"echo $query | psql -d datawarehouse done That would set up 60 (or whatever $HOME/regionlist.txt indicated) partial indices on the table on that field. By the way, I thought ahead a little, in that; doing the same thing for country codes might be as easy as replacing: FIELD=country FILE=$HOME/countrylist.txt The partial indexes will not ALWAYS be useful; in cases where they aren't, it is not inconceivable that there are improvements to be made in the query optimizer... -- let name="cbbrowne" and tld="cbbrowne.com" in String.concat "@" [name;tld];; http://www.ntlug.org/~cbbrowne/linuxxian.html A VAX is virtually a computer, but not quite.
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