hcoona / git-status-cache

High performance cache for git repository status. Clients can retrieve information via named pipe.

git-status-cache

High performance cache for git repository status. Clients can retrieve information via named pipe.

Useful for scenarios that frequently access status information (ex. shell prompts like posh-git) that don't want to pay the cost of a "git status" (significantly more expensive with large repositories) when nothing has changed.

Clients

• PowerShell: git-status-cache-posh-client

Communicating with the cache

Clients connect to the "GitStatusCache" named pipe hosted by GitStatusCache.exe. All messages sent over the pipe must be UTF-8 encoded JSON.

All requests must specify "Version" and "Action". The only currently available version is 1. Should the protocol change in the future the version number will be incremented to avoid breaking existing clients. The following operations may be specified in "Action".

GetStatus

Retrieves current status information for the requested "Path".

Sample request

{
	"Path": "D:\\git-status-cache-posh-client",
	"Version": 1,
	"Action": "GetStatus"
}

Sample response

{
	"Version": 1,
	"Path": "D:\\git-status-cache-posh-client",
	"RepoPath": "D:/git-status-cache-posh-client/.git/",
	"WorkingDir": "D:/git-status-cache-posh-client/",
	"State" : "",
	"Branch" : "master",
	"Upstream": "origin/master",
	"UpstreamGone": false,
	"AheadBy": 0,
	"BehindBy": 0,
	"IndexAdded": [],
	"IndexModified": [],
	"IndexDeleted": [],
	"IndexTypeChange": [],
	"IndexRenamed": [],
	"WorkingAdded": [],
	"WorkingModified": ["GitStatusCachePoshClient.ps1", "GitStatusCachePoshClient.psm1"],
	"WorkingDeleted": [],
	"WorkingTypeChange": [],
	"WorkingRenamed": [],
	"WorkingUnreadable": [],
	"Ignored": [],
	"Conflicted": []
	"Stashes" : [{
			"Name" : "stash@{0}",
			"Sha1Id" : "e24d59d0d03a3f680def647a7bb62f027d8671c",
			"Message" : "On master: Second stash!"
		}, {
			"Name" : "stash@{1}",
			"Sha1Id" : "0cbabd043bae55a76c3c041e6db2b129a0a4872",
			"Message" : "On master: My stash."
		}
	]
}

GetCacheStatistics

Reports information about the cache's performance.

Sample request

{
	"Version": 1,
	"Action": "GetCacheStatistics"
}

Sample response

{
	"Version": 1,
	"Uptime": "01:47:20",
	"TotalGetStatusRequests": 541,
	"AverageMillisecondsInGetStatus": 12.452925,
	"MinimumMillisecondsInGetStatus": 0.098923,
	"MaximumMillisecondsInGetStatus": 213.08858,
	"CacheHits": 383,
	"CacheMisses": 156,
	"EffectiveCachePrimes": 26,
	"TotalCachePrimes": 58,
	"EffectiveCacheInvalidations": 175,
	"TotalCacheInvalidations": 662,
	"FullCacheInvalidations": 0
}

Shutdown

Instructs the cache process to terminate itself.

Sample request

{
	"Version": 1,
	"Action": "Shutdown"
}

Sample response

{
	"Version": 1,
	"Result": "Shutting down."
}

Reporting errors

Any errors with the request will be reported back with a "Version" and a human-readable "Error" message. For example:

{
	"Version": 1,
	"Error": "Requested 'Path' is not part of a git repository."
}

Performance

Cost for serving a cache hit in the cache process is generally between 0.1-0.3 ms, but this metric doesn't include the overhead involved in a full request.

The following measurements were taken on git repositories containing the specified file count. Each file was a text file containing a single sentence of text. Each case was run 5 times and the numbers reported below are averages. Each individual measurement was taken with a high resolution timer at 1 ms precision.

Request from git-status-cache-posh-client

The measurements below capture:

• Serializing a request to JSON in PowerShell.
• Sending the JSON request over the named pipe.
• Compute the current git status (cache miss) or retrieving it from the cache (cache hit) int the cache process.
• Sending the JSON response over the named pipe back to the PowerShell client.
• Deserializing the JSON response into a PSCustomObject

No files modified

	cache miss	cache hit
10 file repository	3.0 ms	1.0 ms
100 file respository	3.0 ms	1.0 ms
1,000 file respository	5.2 ms	1.0 ms
10,000 file respository	22.4 ms	1.0 ms
100,000 file repository	176.6 ms	1.0 ms

10 files modified

	cache miss	cache hit
10 file repository	2.8 ms	1.0 ms
100 file respository	2.8 ms	1.0 ms
1,000 file respository	4.4 ms	1.0 ms
10,000 file respository	20.6 ms	1.0 ms
100,000 file repository	176.6 ms	1.0 ms

Using git-status-cache-posh-client to back posh-git

The measurements below capture all the steps from the git-status-cache-posh-client section as well as the cost for posh-git to render the prompt. This extra step has a fixed cost of around 7-10 ms.

Costs were gathered using timestamps from posh-git's debug output. Timings for posh-git without git-status-cache and git-status-cache-posh-client are included for in the "posh-git without cache" column for reference.

No files modified

	cache miss	cache hit	posh-git without cache
10 file repository	11.8 ms	8.6 ms	57.0 ms
100 file respository	11.8 ms	8.6 ms	62.2 ms
1,000 file respository	14.2 ms	8.6 ms	68.2 ms
10,000 file respository	30.8 ms	8.0 ms	133.8 ms
100,000 file repository	181.6 ms	9.6 ms	754.4 ms

10 files modified

	cache miss	cache hit	posh-git without cache
10 file repository	12.2 ms	9.4 ms	63.2 ms
100 file respository	12.2 ms	9.4 ms	65.0 ms
1,000 file respository	14.4 ms	9.4 ms	72.8 ms
10,000 file respository	31.0 ms	9.4 ms	134.0 ms
100,000 file repository	179.6 ms	9.0 ms	763.6 ms

Build

Need Visual Studio 2022 or higher version.

Need to bootstrap vcpkg before build anything.

cd vcpkg
./bootstrap-vcpkg.bat
cd ..

Then you can build with either Visual Studio 2022 DevEnv or just MSBuild.

start ide/GitStatusCache.sln

Or

msbuild /p:Configuration=Debug /p:Platform=x64
# or for release profile
msbuild /p:Configuration=Release /p:Platform=x64

You can found the artifact in src/GitStatusCache/ide/x64/(Debug|Release)/GitStatusCache.exe.

Verify the dependencies are linked statically:

dumpbin /dependents .\src\GitStatusCache\ide\x64\Debug\GitStatusCache.exe

It would produce as following:

Image has the following dependencies:

  KERNEL32.dll
  USER32.dll
  SHELL32.dll
  SHLWAPI.dll
  WS2_32.dll
  CRYPT32.dll
  RPCRT4.dll
  WINHTTP.dll
  ADVAPI32.dll
  ole32.dll