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Version Control with Subversion
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Version Control with Subversion - Repository Maintenance - Repository Cleanup

Repository Cleanup

Your Subversion repository will generally require very little attention once it is configured to your liking. However, there are times when some manual assistance from an administrator might be in order. The svnadmin utility provides some helpful functionality to assist you in performing such tasks as

  • modifying commit log messages,

  • removing dead transactions,

  • recovering “wedged” repositories, and

  • migrating repository contents to a different repository.

Perhaps the most commonly used of svnadmin 's subcommands is setlog. When a transaction is committed to the repository and promoted to a revision, the descriptive log message associated with that new revision (and provided by the user) is stored as an unversioned property attached to the revision itself. In other words, the repository remembers only the latest value of the property, and discards previous ones.

Sometimes a user will have an error in her log message (a misspelling or some misinformation, perhaps). If the repository is configured (using the pre-revprop-change and post-revprop-change hooks; see the section called “Hook Scripts”) to accept changes to this log message after the commit is finished, then the user can “fix” her log message remotely using the svn program's propset command (see Chapter 9, Subversion Complete Reference ). However, because of the potential to lose information forever, Subversion repositories are not, by default, configured to allow changes to unversioned properties—except by an administrator.

If a log message needs to be changed by an administrator, this can be done using svnadmin setlog . This command changes the log message (the svn:log property) on a given revision of a repository, reading the new value from a provided file.

$ echo "Here is the new, correct log message" > newlog.txt
$ svnadmin setlog myrepos newlog.txt -r 388

The svnadmin setlog command alone is still bound by the same protections against modifying unversioned properties as a remote client is—the pre- and post-revprop-change hooks are still triggered, and therefore must be setup to accept changes of this nature. But an administrator can get around these protections by passing the --bypass-hooks option to the svnadmin setlog command.

Warning

Remember, though, that by bypassing the hooks, you are likely avoiding such things as email notifications of property changes, backup systems which track unversioned property changes, and so on. In other words, be very careful about what you are changing, and how you change it.

Another common use of svnadmin is to query the repository for outstanding—possibly dead—Subversion transactions. In the event that a commit should fail, the transaction is usually cleaned up. That is, the transaction itself is removed from the repository, and any data associated with (and only with) that transaction is removed as well. Occasionally, though, a failure occurs in such a way that the cleanup of the transaction never happens. This could happen for several reasons: perhaps the client operation was inelegantly terminated by the user, or a network failure might have occurred in the middle of an operation, etc. Regardless of the reason, dead transactions can happen. They don't do any real harm, other than consuming a small bit of disk space. A fastidious administrator may nonetheless want to remove them.

You can use svnadmin 's lstxns command to list the names of the currently outstanding transactions.

$ svnadmin lstxns myrepos
19
3a1
a45
$

Each item in the resultant output can then be used with svnlook (and its --transaction option) to determine who created the transaction, when it was created, what types of changes were made in the transaction—in other words, whether or not the transaction is a safe candidate for removal! If so, the transaction's name can be passed to svnadmin rmtxns , which will perform the cleanup of the transaction. In fact, the rmtxns subcommand can take its input directly from the output of lstxns!

$ svnadmin rmtxns myrepos `svnadmin lstxns myrepos`
$

If you use these two subcommands like this, you should consider making your repository temporarily inaccessible to clients. That way, no one can begin a legitimate transaction before you start your cleanup. The following is a little bit of shell-scripting that can quickly generate information about each outstanding transaction in your repository:

Example 5.1. txn-info.sh (Reporting Outstanding Transactions)

#!/bin/sh

### Generate informational output for all outstanding transactions in
### a Subversion repository.

REPOS="${1}"
if [ "x$REPOS" = x ] ; then
  echo "usage: $0 REPOS_PATH"
  exit
fi

for TXN in `svnadmin lstxns ${REPOS}`; do 
  echo "---[ Transaction ${TXN} ]-------------------------------------------"
  svnlook info "${REPOS}" --transaction "${TXN}"
done

You can run the previous script using /path/to/txn-info.sh /path/to/repos . The output is basically a concatenation of several chunks of svnlook info output (see the section called “svnlook”), and will look something like:

$ txn-info.sh myrepos
---[ Transaction 19 ]-------------------------------------------
sally
2001-09-04 11:57:19 -0500 (Tue, 04 Sep 2001)
0
---[ Transaction 3a1 ]-------------------------------------------
harry
2001-09-10 16:50:30 -0500 (Mon, 10 Sep 2001)
39
Trying to commit over a faulty network.
---[ Transaction a45 ]-------------------------------------------
sally
2001-09-12 11:09:28 -0500 (Wed, 12 Sep 2001)
0
$

An long-abandoned transaction usually represents some sort of failed or interrupted commit. A transaction's datestamp can provide interesting information—for example, how likely is it that an operation begun nine months ago is still active?

In short, transaction cleanup decisions need not be made unwisely. Various sources of information—including Apache's error and access logs, the logs of successful Subversion commits, and so on—can be employed in the decision-making process. Finally, an administrator can often simply communicate with a seemingly dead transaction's owner (via email, for example) to verify that the transaction is, in fact, in a zombie state.


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Version Control with Subversion
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