Message-ID: <535E9812.1090605@vmware.com>
Date: Mon, 28 Apr 2014 21:04:02 +0300
From: Heikki Linnakangas <hlinnakangas@vmware.com>
Organization: VMware
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To: Karl Denninger <karl@denninger.net>,
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Subject: Re: Revisiting disk layout on ZFS systems
References: <535E781A.5030708@denninger.net>
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On 04/28/2014 06:47 PM, Karl Denninger wrote:
> What I am curious about, however, is the xlog -- that appears to suffer
> pretty badly from 128k record size, although it compresses even
> more-materially; 1.94x (!)
>
> The files in the xlog directory are large (16MB each) and thus "first
> blush" would be that having a larger record size for that storage area
> would help.  It appears that instead it hurts.

The WAL is fsync'd frequently. My guess is that that causes a lot of 
extra work to repeatedly recompress the same data, or something like that.

- Heikki


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