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Re: ACID Question

To: Rick Spillane <necro351@xxxxxxxxx>
Subject: Re: ACID Question
From: Andi Kleen <ak@xxxxxx>
Date: Mon, 07 Feb 2005 20:04:50 +0100
Cc: linux-xfs@xxxxxxxxxxx
In-reply-to: <ccdab71705020709446c578e99@xxxxxxxxxxxxxx> (Rick Spillane's message of "Mon, 7 Feb 2005 12:44:13 -0500")
References: <ccdab71705020709446c578e99@xxxxxxxxxxxxxx>
Sender: linux-xfs-bounce@xxxxxxxxxxx
User-agent: Gnus/5.110002 (No Gnus v0.2) Emacs/21.3 (gnu/linux)
Rick Spillane <necro351@xxxxxxxxx> writes:

> Does XFS entirely follow the ACID requirements: Atomic, Consistancy,
> Isolated, and Durability?

For user data (read/write) etc. no. It follows POSIX semantics for that, 
which are much weaker.  You can implemented full ACID on top of 
it though using fsync/fdatasync/O_SYNC. 

It probably does for internal transactions on its disk data structures
(like updating directories or inodes), but user visible actions
(rename, create file etc.) are also not necessary atomic or isolated
because the Linux VFS often splits them up into multiple actions.
They should be all consitent in itself though and durable if you
flush the data at some point (fsync).

-Andi


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