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Re: ice-broker scan thread

From: "Qingqing Zhou" <zhouqq(at)cs(dot)toronto(dot)edu>
To: pgsql-hackers(at)postgresql(dot)org
Subject: Re: ice-broker scan thread
Date: 2005-11-29 05:09:11
Message-ID: dmgno1$21n8$ (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
"David Boreham" <david_list(at)boreham(dot)org> wrote
> BTW, I heard a long time ago that NTFS has quite fancy read-ahead, where 
> it attempts to detect the application's access pattern including if it is
> reading sequentially and even if there is a 'stride' to the accesses when
> they're not contiguous. I would imagine that other filesystems attempt 
> similar tricks. So one might expect a simple linear prefectch
> to not help much in the presence of such a filesystem.

So we need more tests. I understand how smart current file systems are, and 
seems that depends on the interval that you send next file block read 
request (decided by cpu_cost parameter in my program).

I imagine on a multi-way machine with strong IO device, the ice-breaker 
could do much better ...

> Were you worried about the icebreaker thread getting too far ahead of the 
> scan ? If it did it might page out the data you're about to read, I think. 
> Of course this could be fixed by having the read ahead thread perodically 
> check the current location being read by the query thread and pausing if 
> it's got too far ahead.



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