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From "Andrew Purtell (JIRA)" <j...@apache.org>
Subject [jira] Created: (HBASE-1968) Give clients access to the write buffer
Date Tue, 10 Nov 2009 04:55:32 GMT
Give clients access to the write buffer

                 Key: HBASE-1968
                 URL: https://issues.apache.org/jira/browse/HBASE-1968
             Project: Hadoop HBase
          Issue Type: Improvement
            Reporter: Andrew Purtell
            Assignee: Andrew Purtell
            Priority: Trivial
             Fix For: 0.20.2

>From a Trend dev team:

When insert rows into one table by calling the method public synchronized void put(final Put
put), if the column family of one row does not exist, the insert operation will failed and
throw NoSuchColumnFamilyException.. We observed that all the following insert operation will
fails even though all of them have valid column family. That is one exception of insert operation
can cause failure of all the following insert operation.

Their further analysis explains in detail the scenario, which I will summarize here:

1) An invalid put is added to the writeBuffer by put(Put put). It will trigger a NoSuchColumnFamilyException
once it goes to the region server.

2) At some point, the buffer is flushed.

3) When the invalid put is processed, an exception is thrown. The finally clause of flushCommits()
removes all successful puts from the writebuffer list but the failed put remains at the top.
This entry becomes an immovable blocker which prevents any subsequent entry from being processed.

4) Subsequent puts will add more entries to the write buffer until the buffer limit is reached,
compounding the problem by allowing more edits to be queued which can never be processed.

A workaround could be for the client to call getWriteBuffer() -- on trunk -- and remove the
entry at the head of the list manually, but without the patch on this issue, the client cannot
get access to the list on branch. 

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