Re: Odd blocking (or massively latent) issue - even with EXPLAIN

Hi Jim,

> 
> I've already tried something very similar using dd. No performance
> penalties during a normal running of the system - or when this blocking
> happens either actually. But I agree, it does indeed sound like some
> sort of I/O problem. I just don't know what! I do have a few more tricks
> up my sleeve that I'll try today. I'll post any results that I have.

Ok, let me know how you get on. 

> 
> That latter test - won't that pretty much just read from the page cache?
> 'sync' may well have forced dirty pages to disk but does it actually
> evict them to?

Basically, the cache is avoided because of the size of the file. 6000000 blocks at 8k exceeds the size of RAM in the machine, so it *should* miss the cache and hit the disk directly. :)

> 
> Anyway, that is off topic... perhaps ;)
> 
> Thanks again,
> 
> Jim
> 

Cheers

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