[FOR TESTING] sparse-checkout with new pattern set #342
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The sparse-checkout feature is mostly hidden to users, as its only documentation is supplementary information in the docs for 'git read-tree'. In addition, users need to know how to edit the .git/info/sparse-checkout file with the right patterns, then run the appropriate 'git read-tree -mu HEAD' command. Keeping the working directory in sync with the sparse-checkout file requires care. Begin an effort to make the sparse-checkout feature a porcelain feature by creating a new 'git sparse-checkout' builtin. This builtin will be the preferred mechanism for manipulating the sparse-checkout file and syncing the working directory. The `$GIT_DIR/info/sparse-checkout` file defines the skip- worktree reference bitmap. When Git updates the working directory, it updates the skip-worktree bits in the index based on this file and removes or restores files in the working copy to match. The documentation provided is adapted from the "git read-tree" documentation with a few edits for clarity in the new context. Extra sections are added to hint toward a future change to a more restricted pattern set. Helped-by: Elijah Newren <[email protected]> Signed-off-by: Derrick Stolee <[email protected]>
Getting started with a sparse-checkout file can be daunting. Help users start their sparse enlistment using 'git sparse-checkout init'. This will set 'core.sparseCheckout=true' in their config, write an initial set of patterns to the sparse-checkout file, and update their working directory. Using 'git read-tree' to clear directories does not work cleanly on Windows, so manually delete directories that are tracked by Git before running read-tree. The use of running another process for 'git read-tree' is likely suboptimal, but that can be improved in a later change, if valuable. Signed-off-by: Derrick Stolee <[email protected]>
When someone wants to clone a large repository, but plans to work using a sparse-checkout file, they either need to do a full checkout first and then reduce the patterns they included, or clone with --no-checkout, set up their patterns, and then run a checkout manually. This requires knowing a lot about the repo shape and how sparse-checkout works. Add a new '--sparse' option to 'git clone' that initializes the sparse-checkout file to include the following patterns: /* !/*/* These patterns include every file in the root directory, but no directories. This allows a repo to include files like a README or a bootstrapping script to grow enlistments from that point. During the 'git sparse-checkout init' call, we must first look to see if HEAD is valid, or else we will fail while trying to update the working directory. The first checkout will actually update the working directory correctly. Signed-off-by: Derrick Stolee <[email protected]>
The 'git sparse-checkout set' subcommand takes a list of patterns as arguments and writes them to the sparse-checkout file. Then, it updates the working directory using 'git read-tree -mu HEAD'. The 'set' subcommand will replace the entire contents of the sparse-checkout file. The write_patterns_and_update() method is extracted from cmd_sparse_checkout() to make it easier to implement 'add' and/or 'remove' subcommands in the future. Signed-off-by: Derrick Stolee <[email protected]>
The 'git sparse-checkout set' subcommand takes a list of patterns and places them in the sparse-checkout file. Then, it updates the working directory to match those patterns. For a large list of patterns, the command-line call can get very cumbersome. Add a '--stdin' option to instead read patterns over standard in. Signed-off-by: Derrick Stolee <[email protected]>
The instructions for disabling a sparse-checkout to a full working directory are complicated and non-intuitive. Add a subcommand, 'git sparse-checkout disable', to perform those steps for the user. Signed-off-by: Derrick Stolee <[email protected]>
When Git updates the working directory with the sparse-checkout feature enabled, the unpack_trees() method calls clear_ce_flags() to update the skip-wortree bits on the cache entries. This check can be expensive, depending on the patterns used. Add trace2 regions around the method, including some flag information, so we can get granular performance data during experiments. This data will be used to measure improvements to the pattern-matching algorithms for sparse-checkout. Signed-off-by: Jeff Hostetler <[email protected]> Signed-off-by: Derrick Stolee <[email protected]>
The sparse-checkout feature can have quadratic performance as the number of patterns and number of entries in the index grow. If there are 1,000 patterns and 1,000,000 entries, this time can be very significant. Create a new Boolean config option, core.sparseCheckoutCone, to indicate that we expect the sparse-checkout file to contain a more limited set of patterns. This is a separate config setting from core.sparseCheckout to avoid breaking older clients by introcuding a tri-state option. The config option does nothing right now, but will be expanded upon in a later commit. Signed-off-by: Derrick Stolee <[email protected]>
The parent and recursive patterns allowed by the "cone mode" option in sparse-checkout are restrictive enough that we can avoid using the regex parsing. Everything is based on prefix matches, so we can use hashsets to store the prefixes from the sparse-checkout file. When checking a path, we can strip path entries from the path and check the hashset for an exact match. As a test, I created a cone-mode sparse-checkout file for the Linux repository that actually includes every file. This was constructed by taking every folder in the Linux repo and creating the pattern pairs here: /$folder/* !/$folder/*/* This resulted in a sparse-checkout file sith 8,296 patterns. Running 'git read-tree -mu HEAD' on this file had the following performance: core.sparseCheckout=false: 0.21 s (0.00 s) core.sparseCheckout=true: 3.75 s (3.50 s) core.sparseCheckout=cone: 0.23 s (0.01 s) The times in parentheses above correspond to the time spent in the first clear_ce_flags() call, according to the trace2 performance traces. While this example is contrived, it demonstrates how these patterns can slow the sparse-checkout feature. Signed-off-by: Derrick Stolee <[email protected]>
To make the cone pattern set easy to use, update the behavior of 'git sparse-checkout [init|set]'. Add '--cone' flag to 'git sparse-checkout init' to set the config option 'core.sparseCheckoutCone=true'. When running 'git sparse-checkout set' in cone mode, a user only needs to supply a list of recursive folder matches. Git will automatically add the necessary parent matches for the leading directories. Signed-off-by: Derrick Stolee <[email protected]>
The sparse-checkout feature in "cone mode" can use the fact that the recursive patterns are "connected" to the root via parent patterns to decide if a directory is entirely contained in the sparse-checkout or entirely removed. In these cases, we can skip hashing the paths within those directories and simply set the skipworktree bit to the correct value. Signed-off-by: Derrick Stolee <[email protected]>
Signed-off-by: Derrick Stolee <[email protected]>
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