Thank you for your reply, John.
I understanded that the bitmap is loading through bitwise OR , but I
do not know how to filter other columns besides col1.
Very appreciate for your help.
Min
On Thu, Oct 29, 2009 at 10:55 PM, K. John Wu <[email protected]> wrote:
> Hi, Min,
>
> FastBit does not currently support the operator 'like'. It has been
> mostly used with numerical values. For string values, the only
> expression supported is equality test.
>
> Assuming you are still interested, here is a quick description of how
> FastBit handles the following statement
>
> select * from table where col1 < 1.5
>
> Given the basic bitmap index, where each distinct value has its own
> bitmap. when FastBit sees that col1 is involved, it will load the
> metadata of the index corresponding to col1. Using the metadata, it
> can figure out which bitmaps needs to be ORed together. Let's say
> col1 are floating-point values, and there are only three values less
> than 1.5: 0, 0.5 and 1, then the bitmaps corresponding to these three
> values marks all the rows that satisfy the condition 'col1 < 1.5.'
> FastBit needs to perform bitwise OR on these three bitmaps. In this
> process, only the necessary bitmaps are read into memory from disk.
>
> If you are interested in more information about how bitmap works in
> general, please take a look at
> <http://en.wikipedia.org/wiki/Bitmap_index>.
>
> Two fairly accessible writeups about FastBit are available at
> <http://ascr-discovery.science.doe.gov/genealogy/fastbit_print.html>
> and <http://www.scidacreview.org/0904/html/fastbit.html>.
>
> John
>
>
> On 10/28/2009 11:08 PM, Min Zhou wrote:
>> Hi guys,
>>
>> if I have a table with 5 columns(col1, col2 ... col5), they will be
>> splitted into 5 files, and col1 be indexed by fastbit.
>> can you describe how fastbit do such a query like
>>
>> select * from tbl where col1 like '%xyz%'
>>
>> I guess fastbit will load bitmaps in memory, fetch the hits by
>> bitmaps, I don't know how fastbit output other columns.
>>
>>
>> Regards,
>> Min
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