On Wed, 9 Nov 2005, TJ O'Donnell wrote:
I like the new bitmap scans and I'm wondering if there is any way
I can utilize them for my bitmask column, defined as bit(1024).
I use this column as a sort of fingerprint to quickly scan my tables.
But it is a scan, not an index. I have not figured out a way to
index the bitmask column. Is there some way it can be used as
an index now that there are bitmap scans in 8.1?
Currently I do this:
Select * from mytable where contains(bitmask, fingerprint(user_data))
and matches(datacolumn, user_data);
user_data is a string, like a regexp but with different semantics for
chemical data.
bitmask is precomputed/stored as bit(1024) = fingerprint(datacolumn)
contains(a,b) returns bool as 'select b=(a&b);'
This works well because matches() is an expensive functions.
But it would work better if bitmask could be indexed, no?
You can use GiST to do that.
TJ O'Donnell
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Oleg
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Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
Sternberg Astronomical Institute, Moscow University (Russia)
Internet: oleg@xxxxxxxxxx, http://www.sai.msu.su/~megera/
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