svnadmin rmtxns — Delete transactions from a repository.
Delete outstanding transactions from a repository. This is covered in detail in the section called “Repository Cleanup”.
Remove named transactions:
$ svnadmin rmtxns /usr/local/svn/repos/ 1w 1x
Fortunately, the output of svn lstxns works great as the input for rmtxns:
$ svnadmin rmtxns /usr/local/svn/repos/ `svnadmin lstxns /usr/local/svn/repos/`
Which will remove all uncommitted transactions from your repository.