[kudu-CR] schema: add is deleted virtual column

["Adar Dembo (Code Review)" <ge...@cloudera.org>]

Hello Tidy Bot, Mike Percy, Dan Burkert, Kudu Jenkins, Grant Henke, Todd Lipcon, 

I'd like you to reexamine a change. Please visit

    http://gerrit.cloudera.org:8080/10968

to look at the new patch set (#10).

Change subject: schema: add is_deleted virtual column
......................................................................

schema: add is_deleted virtual column

This patch introduces a very basic concept of a "virtual column". Virtual
columns borrow from other databases in that they are columns that, rather
than being backed by physical data, are instead backed by Kudu itself. They
may not be part of a schema during table creation/alteration, but may be
added to projections during a scan.

Kudu's virtual columns are defined as logical data types. As data types are
not user-defined, there's no danger of a "collision" between a virtual
column and a physical column as there would be if a virtual column occupied
a well-defined name.

A Kudu subsystem on the scan path that wishes to interact with a virtual
column needs to first figure out if the projection includes it. When
projected, the virtual column's data will be either some default or null
(depending on exactly how it was defined in the projection); it's the
subsystem's responsibility to fill in something meaningful afterwards.

Beyond the basic definition, this patch introduces an IS_DELETED virtual
column derived from BOOL. IS_DELETED will be used to support incremental
backups by describing whether a row was deleted between two timestamps.

Change-Id: I56eb1d44ba8bfbd76d8bb794b8076b695782939e
---
M src/kudu/common/common.proto
M src/kudu/common/schema.cc
M src/kudu/common/schema.h
M src/kudu/common/types.cc
M src/kudu/common/types.h
M src/kudu/master/catalog_manager.cc
M src/kudu/master/master-test.cc
7 files changed, 122 insertions(+), 27 deletions(-)


  git pull ssh://gerrit.cloudera.org:29418/kudu refs/changes/68/10968/10
-- 
To view, visit http://gerrit.cloudera.org:8080/10968
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Gerrit-Project: kudu
Gerrit-Branch: master
Gerrit-MessageType: newpatchset
Gerrit-Change-Id: I56eb1d44ba8bfbd76d8bb794b8076b695782939e
Gerrit-Change-Number: 10968
Gerrit-PatchSet: 10
Gerrit-Owner: Adar Dembo <ad...@cloudera.com>
Gerrit-Reviewer: Adar Dembo <ad...@cloudera.com>
Gerrit-Reviewer: Dan Burkert <da...@apache.org>
Gerrit-Reviewer: Grant Henke <gr...@apache.org>
Gerrit-Reviewer: Kudu Jenkins
Gerrit-Reviewer: Mike Percy <mp...@apache.org>
Gerrit-Reviewer: Tidy Bot
Gerrit-Reviewer: Todd Lipcon <to...@apache.org>