[kudu-CR] Don't output unobservable rows from the MemRowset

["David Ribeiro Alves (Code Review)" <ge...@cloudera.org>]

Hello Kudu Jenkins,

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

    http://gerrit.cloudera.org:8080/4994

to look at the new patch set (#6).

Change subject: Don't output unobservable rows from the MemRowset
......................................................................

Don't output unobservable rows from the MemRowset

In some rare cases we might have a row that is inserted and deleted
in the same operation, meaning the insert and delete have the same
timestamp. In this rare case we might run into trouble later on with
compactions as there is a sequence of operations that that produce
two ghost rows which are uncomparable in terms of recency.

The sequence is as follows:

Insert Row at 1
Delete Row at 3
Flush - Ghost 1 now lives in RS1
Insert Row at 3
Delete Row at 3
Flush - Ghost 2 now lives in RS2
Major delta compact RS1 - GC all before 3
Major delta compact RS2 - GC all before 3

If RS1 and RS2 now get compacted together there is no way to
distinguish Ghost 1 from Ghost 2 and to build a correct history
for the row.

This adds a small test to compaction-test that makes sure that
a row that is inserted and deleted in the same transaction doesn't
appear in the compaction input.

Change-Id: Ieab52a1aa68494218f91f3acd31ef8ddf352bd57
---
M src/kudu/tablet/compaction-test.cc
M src/kudu/tablet/compaction.cc
2 files changed, 147 insertions(+), 56 deletions(-)


  git pull ssh://gerrit.cloudera.org:29418/kudu refs/changes/94/4994/6
-- 
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Gerrit-MessageType: newpatchset
Gerrit-Change-Id: Ieab52a1aa68494218f91f3acd31ef8ddf352bd57
Gerrit-PatchSet: 6
Gerrit-Project: kudu
Gerrit-Branch: master
Gerrit-Owner: David Ribeiro Alves <dr...@apache.org>
Gerrit-Reviewer: Jean-Daniel Cryans <jd...@apache.org>
Gerrit-Reviewer: Kudu Jenkins
Gerrit-Reviewer: Mike Percy <mp...@apache.org>
Gerrit-Reviewer: Tidy Bot
Gerrit-Reviewer: Todd Lipcon <to...@apache.org>