[TieredStorage] HotStorageReader::get_account_offset

[yhchiang-sol]

Problem

HotStorageReader currently has get_account_meta_from_offset() as its
internal get account API for given its offset, but how to obtain the offset
of one account is missing.

Summary of Changes

This PR implements HotStorageReader::get_account_offset, which allows
the HotStorageReader to obtain the offset of one account.

Test Plan

A new test is included in this PR.

[codecov]

Codecov Report

Merging #33824 (baa8616) into master (bdfb644) will increase coverage by 0.0%.
Report is 4 commits behind head on master.
The diff coverage is 100.0%.

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##           master   #33824   +/-   ##
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  Coverage    81.8%    81.8%           
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  Files         809      809           
  Lines      217692   217720   +28     
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+ Hits       178276   178304   +28     
  Misses      39416    39416           

[brooksprumo]

Can you specify offset into what?

Consider also using a newtype to ensure this offset is only used in the correct contexts.

[yhchiang-sol]

Updated the comment. The offset to the account in the underlying TieredStorageFile.

As for creating a new type, does TieredStorageFileOffset or simply TieredStorageOffset look good?

[brooksprumo]

Can you help me remember, is this returned offset a raw byte-offset from the beginning of the file, or something else?

[yhchiang-sol]

It is a raw byte-offset from the beginning of the file (since the accounts block is located at the beginning of a tiered-storage file.)

As for a new type, I have created a #33872 that defines TieredStorageOffset.

[brooksprumo]

It is a raw byte-offset from the beginning of the file (since the accounts block is located at the beginning of a tiered-storage file.)

Is it an offset from the beginning of the file only because the accounts block is located at the beginning of the stored storage file? IOW, if the accounts storage block was not at the beginning, would the returned offset still be from the beginning of the file, or is it an offset from the beginning of the accounts block?

[yhchiang-sol]

Created #34031 based on the recent changes.