Cartesian product to create table takes FOREVER... any way to speed it up?

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Cartesian product to create table takes FOREVER... any way to speed it up?

pietlinden

SSC Guru

Points: 63506
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November 14, 2010 at 11:44 pm

#388228

I think the problem is that I'm trying to create a seriously huge table, and it takes forever...
CREATE TABLE ipaddress(
octet1 tinyint,
octet2 tinyint,
octet3 tinyint,
octet4 tinyint,
primary key(octet1, octet2, octet3, octet4)
);
to populate it, I created a single column table
CREATE TABLE #Temp(
num tinyint PRIMARY KEY);
and then populated the table with all possible values (0-255). That part is fine. When I try to create the insane cartesian product, it takes forever...
Is there any other option than dropping the primary key? It should take a little while, since it's about 16 million records... but how long is reasonable?
It's okay if I limit the tables to (0-15 or 0-31), but if I allow the full range, it just cranks away...
Is this a case of "oh, just go smoke a cigarette and come back." or is this just plain crazy?
thanks,
pieter

Viewing 6 posts - 1 through 5 (of 5 total)

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Philipp Post Default port Points: 1401 More actions · Answer 1

I guess you would receive more input if you give information about your hardware, SQL Server version and the time you mention as "forever".

A CROSS JOIN can be expensive if it produces a large result set, but I am not sure that removing the primary key (read the clustered index it brings) will help you here.

brgds

Philipp Post

Steve Jones - SSC Editor SSC Guru Points: 736478 More actions · Answer 2

One trick that might work, not sure since you havent' provided much info, is to use the "Go trick".

Have smaller cross joins, or variable ones, each one that handles a smaller range, and then use a GO 12.

So maybe each time this executes it cross joins [0..2][0..31], the next time doing [3..4][0..31] using info from the table. Then use a GO 15 to make this build all the rows from 0..30

pietlinden SSC Guru Points: 63506 More actions · Answer 3

Steve Jones - SSC Editor (11/15/2010)
One trick that might work, not sure since you havent' provided much info, is to use the "Go trick".
Have smaller cross joins, or variable ones, each one that handles a smaller range, and then use a GO 12.
So maybe each time this executes it cross joins [0..2][0..31], the next time doing [3..4][0..31] using info from the table. Then use a GO 15 to make this build all the rows from 0..30

Steve,

thanks for validating my suspicions. I tried the join with much smaller datasets and it was very fast. Will try creating a loop to build the table in chunks. Sorry about the lack of info about the server environment... it's on a virtual machine at school... so as far as i know, it could be a piece of junk, and even then I don't know how many VMs are running.

Carl Federl One Orange Chip Points: 25384 More actions · Answer 4

The problem is "populated the table with all possible values (0-255)", results in a table with over 4 billion rows.

select cast(256 as bigint) * 256 * 256 * 256 = 4,294,967,296.

Assuming 4 bytes for the data, plus index, plus storage management, let's round to 16 bytes per row, then you are attempting to build a 64Gb table:

select ( (cast(256 as bigint) * 256 * 256 * 256 ) * 16 ) / (1024 * 1024 * 1024 ) as SpaceGb

If you have not pre-allocated both the database file and the transaction log file to be 64 Gb, then all of the file growths will occur at run time, slowing the process.

SQL = Scarcely Qualifies as a Language

pietlinden SSC Guru Points: 63506 More actions · Answer 5

oh, ouch. I figured it would bring the database to its knees... should have done the math FIRST!!