Slow performance during tag updates with git-branchless

[Kimeiga]

Description of the bug

When running git fetch in a repository with git-branchless enabled, the operation takes an excessively long time when processing a large number of tag updates. The issue appears to be related to how git-branchless processes tag updates sequentially, with each tag being processed individually rather than in batches.

For each tag update, the following output is displayed:

branchless: processing 1 update: ref refs/tags/[tag-name]
 * [new tag]                 [tag-name]                                      -> [tag-name]

This pattern repeats for every single tag being fetched (potentially hundreds of tags), leading to significant performance degradation.

Steps to reproduce:

1. Set up a repository with git-branchless (git branchless init)
2. Configure a remote with many tags (100+)
3. Run git fetch
4. Observe the slow processing of each tag individually with timestamps showing several minutes elapsing

Expected behavior

Git fetch with git-branchless should process tag updates more efficiently, either by:

1. Batching tag updates together for processing instead of handling each one individually
2. Optimizing the processing of individual tags to be faster
3. Providing a configuration option to ignore or batch-process tag updates

The operation should complete in a time comparable to standard git fetch without git-branchless enabled (seconds rather than minutes).

Actual behavior

A simple git fetch operation that should complete in seconds takes several minutes (observed time: approximately 5 minutes based on terminal timestamps). Each tag update is processed individually with verbose output for every single tag.

In a repository with hundreds of tags (particularly in a monorepo with versioned component packages), this creates significant performance overhead. The terminal shows timestamps indicating that the fetch operation is taking much longer than expected (⇣ 4m 59s in the command prompt).

After fetch completes, git status shows the branch is behind by hundreds of commits, suggesting this is a common scenario in repositories with active development and many tags.

Version of rustc

rustc 1.78.0 (9b00956e5 2024-04-29)

Automated bug report

Software version

git-branchless 0.10.0

Operating system

macOS 15.4.1 (Darwin 24.4.0)

Command-line

/Users/hakan.alpay/.cargo/bin/git-branchless bug-report 

Environment variables

SHELL=/bin/zsh
EDITOR=nvim

Git version

> git version 
git version 2.48.1

Hooks

Hooks directory: /Users/hakan.alpay/Projects/web-next-2/.git/hooks

Show 7 hooks

Hook post-applypatch

#!/bin/sh
## START BRANCHLESS CONFIG

git branchless hook post-applypatch "$@"

## END BRANCHLESS CONFIG

Hook post-checkout

#!/bin/sh
## START BRANCHLESS CONFIG

git branchless hook post-checkout "$@"

## END BRANCHLESS CONFIG

Hook post-commit

#!/bin/sh
## START BRANCHLESS CONFIG

git branchless hook post-commit "$@"

## END BRANCHLESS CONFIG

Hook post-merge

#!/bin/sh
## START BRANCHLESS CONFIG

git branchless hook post-merge "$@"

## END BRANCHLESS CONFIG

Hook post-rewrite

#!/bin/sh
## START BRANCHLESS CONFIG

git branchless hook post-rewrite "$@"

## END BRANCHLESS CONFIG

Hook pre-auto-gc

#!/bin/sh
## START BRANCHLESS CONFIG

git branchless hook pre-auto-gc "$@"

## END BRANCHLESS CONFIG

Hook reference-transaction

#!/bin/sh
## START BRANCHLESS CONFIG

# Avoid canceling the reference transaction in the case that `branchless` fails
# for whatever reason.
git branchless hook reference-transaction "$@" || (
echo 'branchless: Failed to process reference transaction!'
echo 'branchless: Some events (e.g. branch updates) may have been lost.'
echo 'branchless: This is a bug. Please report it.'
)

## END BRANCHLESS CONFIG

Events

Show 5 events

Event ID: 78949, transaction ID: 61846 (message: post-merge)

1. CommitEvent { timestamp: 1745875674.0, event_tx_id: Id(61846), commit_oid: NonZeroOid(b132e74c63dfeb7c6e539d06e46e46ac142ffb66) }

:
@ b132e74 16m (> master) xxxxxx xxx xxxxxxxx xx xxxxx xxxxxxxx

Event ID: 78948, transaction ID: 61845 (message: reference-transaction)

1. RefUpdateEvent { timestamp: 1745875729.064352, event_tx_id: Id(61845), ref_name: ReferenceName("refs/heads/master"), old_oid: 244b3efdfc16de29c6a0ab58f81c0a658d188d32, new_oid: b132e74c63dfeb7c6e539d06e46e46ac142ffb66, message: None }

:
@ b132e74 16m (> master) xxxxxx xxx xxxxxxxx xx xxxxx xxxxxxxx

Event ID: 78947, transaction ID: 61843 (message: reference-transaction)

1. RefUpdateEvent { timestamp: 1745875724.979132, event_tx_id: Id(61843), ref_name: ReferenceName("redacted-ref-0"), old_oid: 0000000000000000000000000000000000000000, new_oid: 7bbf9849c56dcd8eacacf55228319ec7ab79018e, message: None }

:
@ b132e74 16m (> master) xxxxxx xxx xxxxxxxx xx xxxxx xxxxxxxx

Event ID: 78946, transaction ID: 61842 (message: reference-transaction)

1. RefUpdateEvent { timestamp: 1745875724.824497, event_tx_id: Id(61842), ref_name: ReferenceName("redacted-ref-1"), old_oid: 0000000000000000000000000000000000000000, new_oid: 54d74b6bfba0c094fa52704f2d4abad66bd7e8a4, message: None }

:
@ b132e74 16m (> master) xxxxxx xxx xxxxxxxx xx xxxxx xxxxxxxx

Event ID: 78945, transaction ID: 61841 (message: reference-transaction)

1. RefUpdateEvent { timestamp: 1745875724.661364, event_tx_id: Id(61841), ref_name: ReferenceName("redacted-ref-2"), old_oid: 0000000000000000000000000000000000000000, new_oid: 7bbf9849c56dcd8eacacf55228319ec7ab79018e, message: None }

:
@ b132e74 16m (> master) xxxxxx xxx xxxxxxxx xx xxxxx xxxxxxxx

Version of git-branchless

git-branchless-opts 0.10.0

Version of git

git version 2.48.1