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From "Enis Soztutar (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-16820) BulkLoad mvcc visibility only works accidentally
Date Thu, 13 Oct 2016 00:09:20 GMT
Enis Soztutar created HBASE-16820:

             Summary: BulkLoad mvcc visibility only works accidentally 
                 Key: HBASE-16820
                 URL: https://issues.apache.org/jira/browse/HBASE-16820
             Project: HBase
          Issue Type: Bug
            Reporter: Enis Soztutar

[~sergey.soldatov] has been debugging an issue with a 1.1 code base where the commit for HBASE-16721
broke the bulk load visibility. After bulk load, the bulk load files is not visible because
the sequence id assigned to the bulk load is not advanced in mvcc. 

Debugging further, we have noticed that bulk load behavior is wrong, but it works "accidentally"
in all code bases (but broken in 1.1 after HBASE-16721). Let me explain: 
 - BL request can optionally request a flush before hand (this should be the default) which
causes the flush to happen with some sequenceId. The flush sequence id is one past all the
cells' sequenceids. This flush sequence id is returned as a result to the flush operation.

 - BL then uses this particular sequenceId to mark the files, but itself does not get a new
sequenceid of its own, or advance the mvcc number. 
 - BL completes WITHOUT making sure that the sequence id is visible. 
 - BL itself though writes entries to the WAL for the BL event, which in 1.2 code bases goes
through the whole mvcc + seqId paths, which makes sure that earlier sequenceIds (the flush
sequenceId) are visible via mvcc. 

The problem with 1.1 is that the WAL entries only get sequence ids, but do not touch mvcc.
With the patch for HBASE-16721, we have made it so that the flushedSequenceId is not used
in mvcc as the highest read point (although all the data is still visible).

BL relying on the flush sequence id is wrong for two reasons: 
 - BL files are loaded with the flush sequence id from the memstore. This particular sequence
id is used twice for two different things and ends up being the sequence id for flushed file
as well as BL'ed files. 
 - BL should make sure that it gets a new sequence id and that sequence id is visible before
returning the results. 

[~ndimiduk] FYI. 

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