dotnet-monitor/documentation/api/gcdump.md

GC Dump - Get

Captures a GC dump of a specified process. These dumps are useful for several scenarios:

• comparing the number of objects on the heap at several points in time
• analyzing roots of objects (answering questions like, "what still has a reference to this type?")
• collecting general statistics about the counts of objects on the heap.

WARNING: To walk the GC heap, this route triggers a generation 2 (full) garbage collection, which can suspend the runtime for a long time, especially when the GC heap is large. Don't use this route in performance-sensitive environments when the GC heap is large.

HTTP Route

GET /gcdump?pid={pid}&uid={uid}&name={name}&egressProvider={egressProvider}&tags={tags} HTTP/1.1

[!NOTE] Process information (IDs, names, environment, etc) may change between invocations of these APIs. Processes may start or stop between API invocations, causing this information to change.

Host Address

The default host address for these routes is https://localhost:52323. This route is only available on the addresses configured via the --urls command line parameter and the DOTNETMONITOR_URLS environment variable.

URI Parameters

Name	In	Required	Type	Description
pid	query	false	int	The ID of the process.
uid	query	false	guid	A value that uniquely identifies a runtime instance within a process.
name	query	false	string	The name of the process.
egressProvider	query	false	string	If specified, uses the named egress provider for egressing the collected GC dump. When not specified, the GC dump is written to the HTTP response stream. See Egress Providers for more details.
tags	query	false	string	(7.1+) A comma-separated list of user-readable identifiers for the operation.

See ProcessIdentifier for more details about the pid, uid, and name parameters.

If none of pid, uid, or name are specified, a GC dump of the default process will be captured. Attempting to capture a GC dump of the default process when the default process cannot be resolved will fail.

Authentication

Authentication is enforced for this route. See Authentication for further information.

Allowed schemes:

• Bearer
• Negotiate (Windows only, running as unelevated)

Responses

Name	Type	Description	Content Type
200 OK	stream	A GC dump of the process when no egress provider is specified.	application/octet-stream
202 Accepted		When an egress provider is specified, the artifact has begun being collected.
400 Bad Request	ValidationProblemDetails	An error occurred due to invalid input. The response body describes the specific problem(s).	application/problem+json
401 Unauthorized		Authentication is required to complete the request. See Authentication for further information.
429 Too Many Requests		There are too many GC dump requests at this time. Try to request a GC dump at a later time.	application/problem+json

[!NOTE] (7.1+) Regardless if an egress provider is specified if the request was successful (response codes 200 or 202), the Location header contains the URI of the operation. This can be used to query the status of the operation or change its state.

Examples

Sample Request

GET /gcdump?pid=21632 HTTP/1.1
Host: localhost:52323
Authorization: Bearer fffffffffffffffffffffffffffffffffffffffffff=

or

GET /gcdump?uid=cd4da319-fa9e-4987-ac4e-e57b2aac248b HTTP/1.1
Host: localhost:52323
Authorization: Bearer fffffffffffffffffffffffffffffffffffffffffff=

Sample Response

The GC dump, chunk encoded, is returned as the response body.

HTTP/1.1 200 OK
Content-Type: application/octet-stream
Transfer-Encoding: chunked
Location: localhost:52323/operations/67f07e40-5cca-4709-9062-26302c484f18

Supported Runtimes

Operating System	Runtime Version
Windows	.NET Core 3.1, .NET 5+
Linux	.NET Core 3.1, .NET 5+
MacOS	.NET Core 3.1, .NET 5+

Additional Notes

When to use pid vs uid

See Process ID pid vs Unique ID uid for clarification on when it is best to use either parameter.

View the collected .gcdump file

On Windows, .gcdump files can be viewed in PerfView for analysis or in Visual Studio. Currently, there is no way of opening a .gcdump on non-Windows platforms.

You can collect multiple .gcdumps and open them simultaneously in Visual Studio to get a comparison experience.

Reports can be generated from .gcdump files using the dotnet-gcdump tool.