On Apr 18, 2007, at 4:28 AM, Alban Hertroys wrote:
I got some good results using bitwise operations on an integer column.
An index on such a column helps a great deal of course. What type of
integer you need depends on how many booleans you (expect to) have.
My operations were like "WHERE (value & 80) = 80" to match against the
7th and 5th bits, with value an int4 column. Query times are in the
tens
of milliseconds range.
Admittedly I only got about that many records through joins with other
tables I needed (meaning that my result set may at some point in time
have been around as big as your data set), so the planner may have
reduced the number of bitwise operations significantly for me.
The actual number of bitwise values to compare was around 40,000
integers * 25 mask values, but that got joined with over 1M records
from
another result set.
A bitwise operator on a single column should (theoretically) have less
overhead than integer/boolean operators on multiple columns. Computers
are good at bitwise operations, after all.
Computers are good at bitwise operations, but software often has
scary implementations :)
thanks for the input. I'll definitely go this route. It was my
first thought, but there is almost no documentation out there for
this type of storage.
// Jonathan Vanasco
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