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Posted to dev@subversion.apache.org by Jani Averbach <ja...@jaa.iki.fi> on 2004/09/16 01:03:19 UTC
Anti-FUD: SVN ate my repository
Hello,
I wrote a document to tackle down a FUD that "after some time SVN
repositories will get corrupted".
If you could read and commend it that would be nice.
The document is located here:
http://www.jaa.iki.fi/~jaa/svn/svn-ate-my-dog.html
If it has seen as correct and not misleading by dev@, I could htmlize
it properly and it could be incorporated to others anti-fud docs.
BR, Jani
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Jani Averbach
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Re: Anti-FUD: SVN ate my repository
Posted by Toby Johnson <to...@etjohnson.us>.
Jani Averbach wrote:
>On 2004-09-16 12:02-0600, Jani Averbach wrote:
>
>There is a new version of my subversion database anti-fud document,
>this time hopefully a little bit more anti than fud.
>
>http://www.jaa.iki.fi/~jaa/svn/svn-ate-my-dog.html
>
>BR, Jani
>
>
Hello Jani, I like version 2.0 much better. :) Good work on gathering
useful info in one source.
I would second Karl's recommendations. Adding the testimonials link
doesn't really address the wedging issue and may make your article lose
its objectivity.
toby
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Re: Anti-FUD: SVN ate my repository
Posted by Max Bowsher <ma...@ukf.net>.
Gregory Burd wrote:
> wedged repository, n:
> A repository in need of repair using available recovery tools.
> Processing cannot continue until the underlying database has been
> rebuilt from the available database log files.
I don't think there has ever been a strict definition of 'wedged', but my
sense (which might be inaccurate) of how it is usually used in the
Subversion world does not agree with the above.
I think 'wedged' is more often used to indicate the state when the databases
and logs are fully consistent, but either a stale lock in the db
environment, or a permissions problem, is blocking access to them.
Max.
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Re: Anti-FUD: SVN ate my repository
Posted by Hamilton Link <he...@sandia.gov>.
I wouldn't use the word 'wedged' at all. It's computer jargon, and it's
not a precise word by any stretch of the imagination. Personally when I
say a machine is wedged it means either the server OR the operating
system OR some piece of my code on that box has seized up and is
unresponsive, and the machine needs to be rebooted OR some bit of
software needs to be restarted, and I haven't bothered to find out
which yet.
FUD stands for Fear, Uncertainty, and Doubt -- how are you going to
combat that by saying "Oh, don't worry, it's just wedged... I can't say
and you don't want to know what the problem is exactly, but running
this-and-that tool almost always fixes it." If a "wedged" repo is in
fact a repo with damaged data structures, use damaged. If it is a repo
that was interrupted in the course of a transaction and was left
locked, say locked. Otherwise find some other suitably precise and
descriptive word and tell me how to verify the DB state and why the
tool in question fixes the problem.
I'd guess the reason Sleepycat doesn't use wedged to describe any
database condition is because they understand the various states it can
get into -- they're knowledgeable, and naturally immune to FUD. Isn't
that the state the anti-fud doc is meant to engender in the reader?
h
> We didn't coin "wedged" and we don't use it to describe any condition
> of DB. :) There are times when recovery (or even catastrophic
> recovery) must be run against a database (DB_RUN_RECOVERY), but that's
> not "wedged".
>
> -greg
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Re: Anti-FUD: SVN ate my repository
Posted by Mark Phippard <Ma...@softlanding.com>.
Gregory Burd <gb...@sleepycat.com> wrote on 09/21/2004 08:49:43 AM:
> wedged repository, n:
> A repository in need of repair using available recovery tools.
> Processing cannot continue until the underlying database has been
> rebuilt from the available database log files.
As a user this definition would scare me because of the word "rebuilt".
What if I do not have all of the log files it needs, etc...? Also, I
think this is actually what the svn devs refer to as a "catastrophic
recovery" but could be wrong, as it sounds like you are referring to the
db_recover process as opposed to what svnadmin recover does. I think a
wedged repository is a bit simpler to fix than this.
> corrupted repository, n:
> A repository with unexpected data within the database and a lack of
> sufficient database log files to effect proper recovery. Proper
> administration of Subversion database resources should prevent this
> from ever happening. Please read the "How to Properly Maintain
> Backups" reference guide for more information.
I would agree that this is probably what a svn dev considers a corrupted
repository. This definition should likely include something indicating
how rare this situation would be, and what factors might likely cause it,
such as bad hardware or ignoring the warning about using networked file
systems.
Mark
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Re: Anti-FUD: SVN ate my repository
Posted by Gregory Burd <gb...@sleepycat.com>.
wedged repository, n:
A repository in need of repair using available recovery tools.
Processing cannot continue until the underlying database has been
rebuilt from the available database log files.
corrupted repository, n:
A repository with unexpected data within the database and a lack of
sufficient database log files to effect proper recovery. Proper
administration of Subversion database resources should prevent this
from ever happening. Please read the "How to Properly Maintain
Backups" reference guide for more information.
-greg
_____________________________________________________________________
Gregory Burd 617-869-0997
Product Manager gburd@sleepycat.com
Sleepycat Software, Inc. http://www.sleepycat.com/
On Sep 20, 2004, at 2:43 PM, Jani Averbach wrote:
> On 2004-09-20 14:18-0400, Mark Phippard wrote:
>>
>> How about attempting to explain what is meant by a "wedged"
>> repository? My
>> assumption has always been that the term "wedged" is something
>> specific
>> for BDB, although maybe it is a common term in the Unix world and
>> people
>> just know what it means? It wasn't until I had read many messages on
>> the
>> mailing list that I started to understand what is meant by it,
>> although I
>> still do not think I could explain it.
>
> Well, I would try.
>
> wedged repository, n: A Subversion repository consists of two
> different internal parts, a working compartment and a storage
> compartment. A wedged repository is a repository where the
> working compartment is unaccessible for some reason, but the
> storage compartment is intact. Therefore wedged repository has
> not suffered any loss of data, but the working compartment has
> to be corrected before you could access the repository. ref:
> corrupted repository.
>
> corrupted repository, n: (See wedged repository for backround) A
> corrupted repository is a Subversion repository, where the
> storage compartment has been damaged, and therefore there are
> some degree of loss of data in the repository.
>
>
> About rest of your comments, I could try to incorporate them, after we
> have found some agreement what a wedeged repository means. =)
> (I think Ben Collins-Sussman is the main suspect for inventing
> a term 'wedged repository'?)
>
> BR, Jani
>
> --
> Jani Averbach
>
>
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Re: Anti-FUD: SVN ate my repository
Posted by Jani Averbach <ja...@jaa.iki.fi>.
On 2004-09-20 14:18-0400, Mark Phippard wrote:
>
> How about attempting to explain what is meant by a "wedged" repository? My
> assumption has always been that the term "wedged" is something specific
> for BDB, although maybe it is a common term in the Unix world and people
> just know what it means? It wasn't until I had read many messages on the
> mailing list that I started to understand what is meant by it, although I
> still do not think I could explain it.
Well, I would try.
wedged repository, n: A Subversion repository consists of two
different internal parts, a working compartment and a storage
compartment. A wedged repository is a repository where the
working compartment is unaccessible for some reason, but the
storage compartment is intact. Therefore wedged repository has
not suffered any loss of data, but the working compartment has
to be corrected before you could access the repository. ref:
corrupted repository.
corrupted repository, n: (See wedged repository for backround) A
corrupted repository is a Subversion repository, where the
storage compartment has been damaged, and therefore there are
some degree of loss of data in the repository.
About rest of your comments, I could try to incorporate them, after we
have found some agreement what a wedeged repository means. =)
(I think Ben Collins-Sussman is the main suspect for inventing
a term 'wedged repository'?)
BR, Jani
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Jani Averbach
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Re: Anti-FUD: SVN ate my repository
Posted by Gregory Burd <gb...@sleepycat.com>.
We didn't coin "wedged" and we don't use it to describe any condition
of DB. :) There are times when recovery (or even catastrophic
recovery) must be run against a database (DB_RUN_RECOVERY), but that's
not "wedged".
-greg
_____________________________________________________________________
Gregory Burd 617-869-0997
Product Manager gburd@sleepycat.com
Sleepycat Software, Inc. http://www.sleepycat.com/
On Sep 20, 2004, at 2:18 PM, Mark Phippard wrote:
> My
> assumption has always been that the term "wedged" is something specific
> for BDB
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Re: Anti-FUD: SVN ate my repository
Posted by Gregory Burd <gb...@sleepycat.com>.
Thanks. I'd agree that its not a BDB specific issue. :) Also,
"corrupted" is not the proper term to use. If DB is used properly by
the application with transactions enabled, if the database and log
files are properly maintained by the user and available for use during
recovery, the database will never be "corrupted". It is in need of
recovery.
If this isn't what's happening right now, we need to figure out why. :)
-greg
_____________________________________________________________________
Gregory Burd 617-869-0997
Product Manager gburd@sleepycat.com
Sleepycat Software, Inc. http://www.sleepycat.com/
On Sep 20, 2004, at 2:46 PM, Michael wrote:
> So I'd label the term as a general computing term, not a BDB/subversion
> specific term. Seems to have a very different meaning than "corrupted".
>
> Michael
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Re: Anti-FUD: SVN ate my repository
Posted by Michael <ec...@yahoo.com>.
--- Mark Phippard <Ma...@softlanding.com> wrote:
> How about attempting to explain what is meant by a "wedged"
> repository? My assumption has always been that the term
> "wedged" is something specific for BDB, although maybe it
> is a common term in the Unix world and people just know
> what it means? It wasn't until I had read many messages on
> the mailing list that I started to understand what is meant
> by it, although I still do not think I could explain it.
Here is the jargon entry for wedged:
1. To be stuck, incapable of proceeding without help. This is
different from having crashed. If the system has crashed, it
has become totally non-functioning. If the system is wedged,
it is trying to do something but cannot make progress; it may
be capable of doing a few things, but not be fully
operational. For example, a process may become wedged if it
deadlocks with another (but not all instances of wedging are
deadlocks). See also gronk, locked up, hosed.
So I'd label the term as a general computing term, not a BDB/subversion
specific term. Seems to have a very different meaning than "corrupted".
Michael
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Re: Anti-FUD: SVN ate my repository
Posted by Mark Phippard <Ma...@softlanding.com>.
kfogel@newton.ch.collab.net wrote on 09/20/2004 11:59:53 AM:
> Jani Averbach <ja...@jaa.iki.fi> writes:
> > I like to get it right first, and after that I will htmlize it and
> > move to more permanent URL. So if you have comments about it, I am
> > all ears.
>
How about attempting to explain what is meant by a "wedged" repository? My
assumption has always been that the term "wedged" is something specific
for BDB, although maybe it is a common term in the Unix world and people
just know what it means? It wasn't until I had read many messages on the
mailing list that I started to understand what is meant by it, although I
still do not think I could explain it.
One of the opening sentences is: "These problems are not corruptions, the
repository is just wedged." Some people may feel that you are just
playing word games and they may not see that there is any difference.
Until the repository is "fixed", it is unusable therefore they do not make
a distinction. Taking the same idea further, perhaps a definition of what
a Subversion developer would call a "corrupted" database would also be
helpful?
I think part of the problem is that people are just loose with their use
of the language. A user might report their database is corrupted without
thinking of the semantic distinction that the developers make in this
area.
So I guess what I am saying is perhaps doing a better job of defining the
"language" to use when talking about these issues would help with the FUD
and give people on the mailing lists something to link to when the terms
are used too loosely.
Mark
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Re: Anti-FUD: SVN ate my repository
Posted by kf...@collab.net.
Jani Averbach <ja...@jaa.iki.fi> writes:
> I like to get it right first, and after that I will htmlize it and
> move to more permanent URL. So if you have comments about it, I am
> all ears.
Just a few:
The claim that "SVN repository will get corrupted after some time"
is a false accusation.
==>
The claim that "SVN repository will get corrupted after some time"
is false.
And, maybe remove this sentence:
See testimonials of Subversion, if you don't believe:
http://subversion.tigris.org/propaganda.html.
...since the testimonials don't prove anything, they're success
stories only, by definition. (You could certainly link to the
testimonials/propaganda page from your document, I just think it's
better not to offer it as proof of any particular fact.)
"Backup" should be "Back up" when used as a verb, I think.
And lastly, you might want to turn it into real HTML, so the links
work and the initial pseudo-quote could be offet in italics or
something.
Thanks for writing it!
-Karl
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Re: Anti-FUD: SVN ate my repository
Posted by Jani Averbach <ja...@jaa.iki.fi>.
On 2004-09-20 07:53-0500, kfogel@collab.net wrote:
> Jani Averbach <ja...@jaa.iki.fi> writes:
> > There is a new version of my subversion database anti-fud document,
> > this time hopefully a little bit more anti than fud.
> >
> > http://www.jaa.iki.fi/~jaa/svn/svn-ate-my-dog.html
>
> Will this be a permanent URL, that others can link to?
No,
I like to get it right first, and after that I will htmlize it and
move to more permanent URL. So if you have comments about it, I am
all ears.
BR, Jani
--
Jani Averbach
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Re: Anti-FUD: SVN ate my repository
Posted by kf...@collab.net.
Jani Averbach <ja...@jaa.iki.fi> writes:
> There is a new version of my subversion database anti-fud document,
> this time hopefully a little bit more anti than fud.
>
> http://www.jaa.iki.fi/~jaa/svn/svn-ate-my-dog.html
Will this be a permanent URL, that others can link to?
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Re: Anti-FUD: SVN ate my repository
Posted by Jani Averbach <ja...@jaa.iki.fi>.
On 2004-09-16 12:02-0600, Jani Averbach wrote:
There is a new version of my subversion database anti-fud document,
this time hopefully a little bit more anti than fud.
http://www.jaa.iki.fi/~jaa/svn/svn-ate-my-dog.html
BR, Jani
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Jani Averbach
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Re: Anti-FUD: SVN ate my repository
Posted by Jani Averbach <ja...@jaa.iki.fi>.
On 2004-09-16 09:54-0400, Toby Johnson wrote:
>
> If I knew nothing about Subversion, I would feel *less* comfortable with
> it after reading your document. Since your stated goal is "anti-FUD",
> I'm assuming that isn't what you were trying to accomplish.
>
Thanks Toby for your comments, I have to rephrase it.
Br, Jani
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Re: Anti-FUD: SVN ate my repository
Posted by Toby Johnson <to...@etjohnson.us>.
Jani Averbach wrote:
>Hello,
>
>I wrote a document to tackle down a FUD that "after some time SVN
>repositories will get corrupted".
>
>If you could read and commend it that would be nice.
>
>
If I knew nothing about Subversion, I would feel *less* comfortable with
it after reading your document. Since your stated goal is "anti-FUD",
I'm assuming that isn't what you were trying to accomplish.
I could basically paraphrase the top section as "sometimes when people
think their repository is corrupted, it's really just wedged, but
sometimes it really is corrupted and you've lost data". Hardly a very
comforting way to start out a FAQish document.
You then go on to describe wedged repositories and why it might happen.
But then you go into "real" corruption, where you give a good point
about NFS/SMB shares and disk space, but the rest is basically saying
"yeah, sometimes data is lost, and I really don't know why".
If I'm looking into Subversion and I see "Unclassified corrupted
repositories: I think that I have seen a couple cases when there has not
been any particular reason for database corruption", I'm running the
other way as fast as I can. What are these instances of corruption you
"think you've seen"? From there, you talk about Berkeley DB being "too
brittle". Again, not very reassuring.
I wouldn't say any of this is factually incorrect, but it's all
presented in the wrong way. If you're trying to dispel FUD, then make no
mention of any of this until the very end and say something like "of
course, no computer is 100% bulletproof so be sure to always make
backups of your data", which you've already described somewhat. Saying
"yeah, I think I've seen some data corruption but it might have been a
burnt CPU or something" is not a good way to dispel myth.
Unless you know of any particular cases of corruption, then don't
speculate on it; that will only make others more wary. I'm not
suggesting you hide the truth, but I know of no true cases of corruption
that were Subversion or BerkeleyDB's fault.
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