Andrew Wong has posted comments on this change. ( 
http://gerrit.cloudera.org:8080/11248 )

Change subject: KUDU-2469 pt 1: add an IOContext
......................................................................


Patch Set 1:

(1 comment)

http://gerrit.cloudera.org:8080/#/c/11248/1/src/kudu/fs/io_context.h
File src/kudu/fs/io_context.h:

http://gerrit.cloudera.org:8080/#/c/11248/1/src/kudu/fs/io_context.h@33
PS1, Line 33: // Utility class used to pass strings across many layers, 
avoiding excessive
            : // plumbing.
> You're right it's a one-time cost, though I leaned this way since the inten
I'd considered going through hte iters, but there are a couple paths to CFiles 
that weren't covered just going through the scan path:

- We also want the context when we Open() the Tablet; we need to read the 
min/max keys to populate the rowset tree, and open blooms (lazily).
- Whenever we insert, we check if the row is present.

If we did want to plumb the IOContext _only_ where we might do IO, these cases 
would need to be covered too. OTOH, these other cases (and scans via the iters) 
roughly go through the same call chain:

 Tablet-->DiskRowSet-->CFileSet-->{BloomFileReader/CFileReader}
               `->DeltaTracker-->DeltaFileReader-->CFileReader

We could plumb down the IOContext through the constructors of these classes. 
Less in the spirit of plumbing only when we do IO, but that's not really a 
requirement.



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Gerrit-Project: kudu
Gerrit-Branch: master
Gerrit-MessageType: comment
Gerrit-Change-Id: I645e10a2fda1f2564326b7052e6a0debc5ad738c
Gerrit-Change-Number: 11248
Gerrit-PatchSet: 1
Gerrit-Owner: Andrew Wong <[email protected]>
Gerrit-Reviewer: Adar Dembo <[email protected]>
Gerrit-Reviewer: Andrew Wong <[email protected]>
Gerrit-Reviewer: Grant Henke <[email protected]>
Gerrit-Reviewer: Kudu Jenkins
Gerrit-Reviewer: Todd Lipcon <[email protected]>
Gerrit-Comment-Date: Fri, 17 Aug 2018 01:30:19 +0000
Gerrit-HasComments: Yes

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