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Re: Restarting Apache during a commit through a proxy

From: Philip Martin <philip.martin_at_wandisco.com>
Date: Tue, 01 Mar 2011 10:38:55 +0000

Philip Martin <philip.martin_at_wandisco.com> writes:

> I've been thinking about this overnight and I believe I need to do more
> investigation on the WANdisco side.

I now realise I was mistaken about this problem. The fact that we don't
fsync during a transaction doesn't affect Apache restarts. When Apache
acknowledges an http request all the file descriptors to the repository
associated with processing that request have been closed and so all data
written has moved from user-space to kernel-space. The fact that it is
not on disk doesn't matter, it will be visible to other processes. The
absence of fsync could make a difference is if the machine, rather than
just Apache, were restarted, and I suppose a client/proxy could attempt
one commit that spanned a machine restart, but I'm not going to worry
about it.

The problem that was seen during WANdisco testing occurred when Apache
was restarted after a commit had happened in the repository but before
Apache could acnowledge the http request. When this happens the
transaction associated with the commit may still exist, or may have been
partially or fully removed. That's simply normal operation.

Received on 2011-03-01 11:39:38 CET

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