Apache Subversion 1.15 Release Notes

Background ¶

All Subversion working copies require extra storage space for the working copy administrative directory (.svn). By default, the storage space required for this administrative directory is slightly more than the total size of the checked out files. Subversion uses most of that extra space to cache a copy of each file's BASE revision ("pristine") so that operations such as diff and revert can work offline, and commit can send just the modified portions of a file to the repository server rather than the whole file.

This design optimises the speed and availability of these operations on the assumption that network connectivity to the repository may be a bottleneck (or unavailable at times) while local storage is assumed to be inexpensive.

However, in some use cases, it may be more sensible to fetch pristines from the repository server only when needed ("on demand"), rather than to cache all pristines all the time. Some example use cases:

• Very large files that change infrequently. In this case, the pristine is usually not needed but takes up space, doubling the storage requirement while providing little or no benefit.
• Working copies on storage-constrained devices with a fast, always-on connection to the repository server. In this case, network bandwidth is more readily available than local storage, inverting the original design assumption that local storage is inexpensive.
• Working copies on the same device as the repository.

When using Pristines On Demand, instead of caching pristines for all files all the time, Subversion will only fetch and cache those of individual files when needed, and will eliminate them when no longer needed.

Tradeoffs ¶

The space savings come with some tradeoffs:

A Subversion 1.15 or newer client is required to operate on the working copy. The working copy cannot be used interchangeably with Subversion 1.8 through 1.14 clients, as these will report an error.

A connection to the repository server is required for more operations as compared to a fully-cached working copy. Depending on network speeds and file sizes, the additional network communications may introduce a perceptible delay when a pristine is downloaded.

Checking Out a Pristines On Demand Working Copy ¶

As of Subversion 1.15, users can opt for Pristines On Demand at checkout time by giving the --store-pristine=no option. This applies to the entire working copy:

$ svn checkout --store-pristine=no $REPO $WC

Otherwise, the default is to check out a normal, fully cached working copy:

$ svn checkout $REPO $WC

Users may also write --store-pristine=yes to explicitly request a a normal, fully cached working copy. This may be useful in scripting scenarios:

$ svn checkout --store-pristine=yes $REPO $WC

Examining the Working Copy Pristines Type ¶

Users can check whether a working copy uses Pristines On Demand with the svn info command. This command shows several fields which are new in Subversion 1.15, shown in bold here:

$ svn info
Path: .
Working Copy Root Path: /ramdrive/svn-trunk
Working Copy Compatible With Version: 1.15
Working Copy Format: 32
Working Copy Store Pristine: no
URL: https://svn.apache.org/repos/asf/subversion/trunk
Relative URL: ^/subversion/trunk
Repository Root: https://svn.apache.org/repos/asf
Repository UUID: 13f79535-47bb-0310-9956-ffa450edef68
Revision: 1924024
Node Kind: directory
Schedule: normal
Last Changed Author: dsahlberg
Last Changed Rev: 1923965
Last Changed Date: 2025-02-21 11:08:37 -0500 (Fri, 21 Feb 2025)

The relevant one is Working Copy Store Pristine. This shows no when using Pristines On Demand (coinciding with the --store-pristine=no command line switch), yes when using a normal, fully cached working copy (coinciding with --store-pristine=yes).

Repository Access Comparison ¶

The following table lists the Subversion commands that behave differently when using Pristines On Demand. For each command, it shows the difference in how that command accesses the repository.

Legend:

• Never: Does not contact the repository server.
• Always: Always contacts the repository server.
• Hydrate: This operation downloads and keeps the pristine for each file that has a local content modification (i.e., when svn status shows M in the 1st column) when its pristine is not already stored in the working copy. See notes 1 and 2 below.
• Send-Delta: Sends just the locally modified parts of each file's content.
• Send-Full: Sends the complete content of each locally modified file.

Additional Details ¶

Once downloaded, Subversion keeps a file's pristine locally cached in the working copy administrative directory so that further operations on the file will not download it from the repository again. Subversion keeps the pristine until an operation either restores the file to an unmodified state or detects that the file is no longer modified. For example, commit and revert will immediately discard the pristine of each file they operated on, because that file will no longer be locally modified, whereas diff will discard the pristine only if it finds there are no differences.

Note 1: At the beginning of a given operation, Subversion will download missing pristines of at least the files that this particular operation will use. It may download those of other files too, that this particular operation will not use. For example, in the initial implementation of this feature, Subversion considers all potential files in the smallest subtree that spans all the target files of the operation. The details of this behaviour are subject to change before and after the feature is released.

Note 2: In evaluating differences between a file's working text and its BASE text, Subversion takes into account the "EOL style" and "keywords" settings. (See the svn:eol-style and svn:keywords properties.) Just as svn status does not show M in the first column for such differences, neither will these cause the pristine to be downloaded from the repository.

Limitations and Future Possibilities ¶

Currently, this feature applies to an entire working copy. That is, either all working files have their pristines cached (the default) or all working files use pristines on demand (--store-pristine=no). In the future, this feature may be enhanced to give users more granular control, such as by allowing the --store-pristine switch to apply to individual files.

TODO: Point to the "User Guide" in notes/i525/. Regenerate /docs/i525-user-guide.html from the source markdown.

Supported Working Copy Formats ¶

Subversion 1.15 supports working copies in two format versions:

Subversion 1.15 uses Format 31 by default, unless the user selects Format 32 explicitly or opts in to Pristines On Demand.

Future releases may introduce newer working copy formats while keeping support for existing formats.

New Command Line Options ¶

Two new command line options allow users to control the working copy format:

--store-pristine=ARG can be used with svn checkout:

• --store-pristine=no: requests a working copy with Pristines On Demand. This option implies working copy Format 32, supported by 1.15 and newer clients.
• --store-pristine=yes (default): requests a working copy with traditional fully-cached Pristines. By default, the working copy will use Format 31, supported by 1.8 and newer clients, unless overridden by --compatible-version=1.15; see below.

--compatible-version=ARG, where ARG is a version of Subversion, can be used with svn checkout and svn upgrade:

This requests the newest working copy format that is compatible with the specified Subversion client version.

When choosing ARG, specify the version of the oldest Subversion client that will be used with the working copy.

ARG may be in MAJOR.MINOR format, such as 1.9. ARG may also specify a patch version, such as 1.9.5 but the third component is ignored because Subversion does not introduce new working copy metadata formats in patch releases.

• --compatible-version=1.8 through --compatible-version=1.14 (default): requests a working copy in Format 31, supported by Subversion 1.8 and newer clients. Supports traditional fully-cached Pristines only.
• --compatible-version=1.15: requests a working copy in Format 32, supported by Subversion 1.15 and newer clients. Although this format supports Pristines On Demand, it will use traditional fully-cached Pristines by default, unless overridden by --store-pristine=no; see above.

The following table shows which format and pristine type is achieved by each combination of the --store-pristine and --compatible-version switches (including when omitting one or both of these):

New svn info Output ¶

Users can determine the working copy format and pristine storage type with the svn info command (new fields shown in bold):

$ svn info
Path: .
Working Copy Root Path: /ramdrive/svn-trunk
Working Copy Compatible With Version: 1.15
Working Copy Format: 32
Working Copy Store Pristine: no
URL: https://svn.apache.org/repos/asf/subversion/trunk
Relative URL: ^/subversion/trunk
Repository Root: https://svn.apache.org/repos/asf
Repository UUID: 13f79535-47bb-0310-9956-ffa450edef68
Revision: 1924024
Node Kind: directory
Schedule: normal
Last Changed Author: dsahlberg
Last Changed Rev: 1923965
Last Changed Date: 2025-02-21 11:08:37 -0500 (Fri, 21 Feb 2025)

Explanation of the new fields:

• Working Copy Compatible With Version shows the oldest Subversion client that can be used with this working copy. In this release, this field may show 1.8 or 1.15.
• Working Copy Format shows the working copy format version. In this release this field may show 31 or 32.
• Working Copy Store Pristine shows no when using Pristines On Demand, yes when using traditional fully-cached pristines.

Older Subversion Clients ¶

When using the newer Format 32, a Subversion 1.15 or newer client is required. Attempting to operate on such a working copy with an older client will result in an error, such as:

svn: E155021: This client is too old to work with the working copy at
'/path/to/working/copy' (format 32).
You need to get a newer Subversion client. For more details, see
  http://subversion.apache.org/faq.html#working-copy-format-change

Additional Notes ¶

The metadata format is a property of a particular working copy. Users may have multiple working copies on their machine, with some in Format 31 and others in Format 32.

Plaintext credential cache is supported by default on Unix-like systems ¶

Subversion supports several credential caches to prevent re-typing usernames and passwords repeatedly. Which credential cache(s) are used depends on the operating system, compile-time options, and the user's runtime configuration. On Windows and macOS, Subversion uses OS facilities to save passwords in encrypted form. Unix-like operating systems do not have a single standard facility to do this; on these systems, Subversion supports up to four credential caches: GNOME Keyring, KWallet, GPG Agent, and (as a fallback) the Plaintext cache.

The rest of this section discusses the Plaintext cache and is applicable only to Subversion clients running on Unix-like operating systems.

In Subversion 1.12 through 1.14, write access to the Plaintext cache was disabled by default at compile-time. Binaries compiled in the default configuration could not store new plaintext credentials, but would continue to use any that were already stored. Users and binary packagers could explicitly enable write access to the Plaintext cache by compiling Subversion with the --enable-plaintext-password-storage option to configure. (See r1845377.)

Unfortunately, this has caused a variety of problems for users, especially when using the svn client in unattended processes such as CI systems, or on remote machines through ssh (a GUI password prompt would display on the remote machine, inaccessible to the ssh user). Users reported that they had to employ workarounds that caused passwords to be stored in plaintext anyway, or refused to upgrade their Subversion installations to these releases. Some binary packagers built with --enable-plaintext-password-storage while others didn't, creating inconsistent experiences within the same release lines.

Based on the feedback received, Subversion 1.15 inverts the default. (See r1909351.) Binaries compiled in the default configuration can once again store new plaintext credentials (after warning and asking the user). Sites that wish to eliminate this possibility can do one or both of the following:

• Compile Subversion with the --disable-plaintext-password-storage option to configure or install a binary package that was compiled this way. Be aware that users can circumvent this by compiling or installing their own Subversion binaries and/or by creating a plaintext cache manually.
• Allow encrypted stores like GNOME Keyring and KWallet, but not the Plaintext cache, by setting store-plaintext-passwords = no in Subversion's run-time config settings. See the per user files at ~/.subversion/config and ~/.subversion/servers, and the systemwide files at /etc/subversion/config and /etc/subversion/servers.

For more on plaintext credentials, see the FAQ entry.