Should vector be maintaining open file handles to `ignore_older` files older than the cutoff?

I'm not sure if this is a bug or expected behavior, but it looks like, when using the ignore_older config for the file source, Vector still maintains an open file handle to the files with a modified time before the cutoff.

From gitter: https://gitter.im/timberio-vector/community?at=5f456c28c3aa024ef99e4907 . The user was trying to limit the number of open file handles, by using the ignore_older config.

If it is expected, we should probably call it out in the docs as I was not expecting that. It seemingly limits its usefulness in avoiding resource consumption.

Vector Version

vector 0.11.0 (g8b4ff32 x86_64-unknown-linux-gnu 2020-08-25)

Vector Configuration File

data_dir = "/tmp/vector"

[sources.in]
  type = "file" # required
  ignore_older = 10  # optional, no default, seconds
  include = ["/tmp/log/*.log"] # required

[sinks.http]
  type = "console"
  inputs = ["in"]
  encoding.codec = "json"

Debug Output

Aug 25 16:57:23.252  INFO vector: Log level "debug" is enabled.
Aug 25 16:57:23.256  INFO vector: Loading configs. path=["/tmp/test.toml"]
Aug 25 16:57:23.276  INFO vector::topology: Running healthchecks.
Aug 25 16:57:23.276  INFO vector::topology: Starting source "in"
Aug 25 16:57:23.277  INFO vector::topology::builder: Healthcheck: Passed.
Aug 25 16:57:23.277  INFO vector::topology: Starting sink "http"
Aug 25 16:57:23.277  INFO vector: Vector has started. version="0.11.0" git_version="v0.9.0-573-g8b4ff32" released="Tue, 25 Aug 2020 20:48:03 +0000" arch="x86_64"
Aug 25 16:57:23.277  INFO source{name=in type=file}: vector::sources::file: Starting file server. include=["/tmp/log/*.log"] exclude=[]
Aug 25 16:57:23.279  INFO source{name=in type=file}:file_server: vector::internal_events::file: found new file to watch. path="/tmp/log/a.log"
Aug 25 16:57:23.280 DEBUG source{name=in type=file}:file_server: vector::internal_events::file: files checkpointed. count=0
Aug 25 16:57:24.315 DEBUG source{name=in type=file}:file_server: vector::internal_events::file: files checkpointed. count=0
Aug 25 16:57:25.340 DEBUG source{name=in type=file}:file_server: vector::internal_events::file: files checkpointed. count=0
Aug 25 16:57:27.391 DEBUG source{name=in type=file}:file_server: vector::internal_events::file: files checkpointed. count=0
^CAug 25 16:57:28.368  INFO vector: Vector has stopped.
Aug 25 16:57:28.370  INFO vector::topology: Shutting down... Waiting on: in, http. 59 seconds left
Aug 25 16:57:28.370 DEBUG source{name=in type=file}: vector::topology::builder: Finished
Aug 25 16:57:28.370 DEBUG sink{name=http type=console}: vector::topology::builder: Finished

Expected Behavior

Vector does not open the file

Actual Behavior

Vector opens the file

Additional Context

$ lsof -p 27049 | grep a.log
vector  27049 CORP\jesse   15r      REG              259,3    104581 178538005 /tmp/log/a.log