Benchmark: Gitaly with OverlayFs

Objective

OverlayFS has been in experimentation phase. See !8033

Once that is ready, we should benchmark with and without the use overlayfs.

Scope

• Use the standard Ext4 system
• Workloads: The current mix of RPCs defined in master's k6-benchmark.js is a minimum workload that needs to be run. If additional workloads with different RPCs need to be run, start another report.
• Test with OverlayFS enabled vs Gitaly with Transactions enabled

It is configurable in the config.toml:

[Transactions]
Enabled = true
Driver = "overlayfs"

OverlayFS Matrix

• Kernel versions and overlayfs parameters: index=on/off, redirect_dir=on/off, metacopy=on/off, xino=on/off
• lowerdir/upperdir/workdir on same device

Documentation Requirements

• Mount options used for overlayfs

Deliverables

• Reproducible benchmark results using #6732 framework
• Performance comparison tables/plots
• Analysis of the benchmarks
• Post to this issue