On 6 Jun, 15:08, Daniele <dankan775removet...@yahoo.it> wrote:
> Captain Paralytic wrote:
> >> I read about join is not advice on big table as it will create a
> >> instance of the 2 table in one
> >> but I will try
> >> thanks- Hide quoted text -
>
> >> - Show quoted text -
>
> > WHAT???
>
> > Please could you point me to where you read that?
>
> from:http://www.mysqlperformanceblog.com/...l-could-be-slo....
> I think that my speed reading jump an important part( the last line of
> this paragraph
>
> "Here is good example. As we saw my 30mil rows (12GB) table was scanned
> in less than 5 minutes. Now if we would do eq join of the table to other
> 30mil rows table and it will be completely random. We'll need to perform
> 30 millions of random row reads, which gives us 300.000 seconds with 100
> rows/sec rate. So we would go from 5 minutes to almost 4 days if we need
> to do the join. Some people assume join would be close to two full table
> scans (as 60mil of rows need to be read) - this is way wrong."
>
> but i'm not sure about this
> "Avoid joins to large tables *Joining of large data sets using nested
> loops is very expensive. Try to avoid it. Joins to smaller tables is OK
> but you might want to preload them to memory before join so there is no
> random IO needed to populate the caches."

Oh pleeeese!

This is nothing like what you are trying to do.