Thread: Performance of Bit String

Hi,<br /><br />I tried to store a BitString of length 2 million in a Postgres table (see code below), but it did not
completeeven in 3 mins and then I cancelled it. Surprisingly, it only took few seconds when BitString was of length
500K.Is there any restriction of length of BitString or am I missing something here? <br /><br />create table
bit_test(<br/> id smallint,<br /> memset bit(200000)<br /> ) ;<br /><br />DECLARE<br /> memset bit varying:= B'0';<br
/>BEGIN<br/> --PERFORM memset;<br /> FOR i In 1..2000000 LOOP<br /> memset := (memset || B'1') ; -- (B'1' <<
i);<br/> END LOOP;<br /><br /> INSERT INTO bit_test VALUES(1,B'1',memset :: bit(2000000));<br /><br />RETURN
bit_length(memset);<br/>END;<br /><br /><br />Thanks,<br />Rupendra 

Hi,

Youre on the wrong list for this. This is not a -hackers (i.e. developer 
targeted) but a -general (user targeted) question.


On Wednesday 09 June 2010 15:11:41 rupendra.chulyadyo@gmail.com wrote:
> I tried to store a BitString of length 2 million in a Postgres table (see
> code below), but it did not complete even in 3 mins and then I cancelled
> it. Surprisingly, it only took few seconds when BitString was of length
> 500K. Is there any restriction of length of BitString or am I missing
> something here?
I think youre missing that your algorithm for assembling the string has 
quadratic complexity.
For each loop iteratoring the whole string will be newly allocated and then 
copied over.

A faster way to create such a long string might be:
SELECT array_to_string(array_agg(1),'')::bit(2000000) FROM generate_series(1, 
2000000);

Btw, your table definition has only the length bit(200k), but youre inserting 
bit(2000k)...


What are you trying to achieve with such a long bitstring? Actually I cannot 
think of any database design where I would consider that a valid design-
choice.


Andres