[jira] [Created] (ARROW-16928) [C++] Reconsider filesystem equality

["Antoine Pitrou (Jira)" <ji...@apache.org>]

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[Antoine
Pitrou](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=apitrou)
**created** an issue  
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[ARROW-16928](https://issues.apache.org/jira/browse/ARROW-16928)  
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[[C++] Reconsider filesystem
equality](https://issues.apache.org/jira/browse/ARROW-16928)  
| Issue Type: |  ![Task](cid:jira-generated-image-
avatar-88471a72-3446-49d0-a893-66aa2719cebe) Task  
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Assignee: |  Unassigned  
Components: |  C++  
Created: |  28/Jun/22 17:30  
Priority: |  ![Minor](cid:jira-generated-image-static-
minor-f6a7db0a-de21-4e3f-a157-c50b723f286c) Minor  
Reporter: |  [Antoine
Pitrou](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=apitrou)  
|

Filesystems support an equality method to compare filesystem instances. The
original idea is that all filesystem parameters should be transparent and
easily read back, so it should be possible to support equality (similarly, it
was envisioned to allow roundtripping filesystems through URIs, though the
filesystem-to-URI direction was never implemented).

However, along the way, filesystems like S3 grew increasingly complex and
opaque modes of configuration where equality can only be approximated. It can
also be costly to compute (for example, `S3Options::Equals` involves fetching
the actual secret key and session token, which can take some time: these mere
operations consume 5 seconds in the PyArrow test suite).

Right now, filesystem equality is merely used for testing on the Python side
(to try and validate filesystem pickling).

We should decide whether we want to continue supporting filesystem equality
and, if so, what the semantics are (is approximate equality useful?).  
  
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