Add temporary way to configure amount of data prefetched per file handle #1021
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This can be removed at any time. Signed-off-by: Daniel Carl Jones <[email protected]>
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Sep 18, 2024
Signed-off-by: Daniel Carl Jones <[email protected]>
Signed-off-by: Daniel Carl Jones <[email protected]>
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Description of change
In some use cases (such as those in multi-tenant settings), a very large number of file handles may be opened concurrently. While the default prefetching works fine for environments with fewer open file handles, we see that Mountpoint can use far too much memory otherwise.
This change introduces a temporary way to scale down the maximum amount that Mountpoint will prefetch per file handle. Today, the default is 2GiB and the new parameter can be used to reduce that.
The end goal is to make this parameter obsolete through the work in #987 to make prefetching scale down when available memory is low.
Relevant issues: #502, #566, #630, #987
Does this change impact existing behavior?
No existing behavior is impacted. This allows a temporary way to override the prefetch window size.
When it is removed, it will not trigger any issue (so long as the root cause is solved on memory usage). We use an environment variable such that this can be removed without breaking deployments.
Does this change need a changelog entry in any of the crates?
This change does not add a changelog entry as we do not recommend using this override.
By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and I agree to the terms of the Developer Certificate of Origin (DCO).