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https://issues.apache.org/jira/browse/HBASE-18066?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16018583#comment-16018583
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stack commented on HBASE-18066:
-------------------------------
bq. ... but I do not know the history of this method so let's wait for a while.
We have getClosestRowBefore because we did not have a reverse Scan. We have to
reverse Scan as part of 'normal' operation because we made a mistake doing the
schema for hbase;meta*.
* hbase:meta is made with keys that are the regioninfo serialized. The
regioninfo name includes the startrow of the region so in hbase:meta keys are
sorted first by table and then by region startkeys. Scans run in the sort
direction which means when looking for the region that hosts a key we scan
hbase:meta and have to keep going until we hit a key that is greater than the
one we are looking for. This key will be in a region-too-far; i.e. the start
row of region that follows the one we want. So, the Scan has gone to far and we
need to back up to find the region that hosts the key we are looking for. If
the hbase:meta were made of keys that had table name and region end key, then
when we found a key that was beyond the one we were looking for, the Scan would
be in the region hosting that wanted key; no need to back up.
We should have been smarter and realized our mistake sooner. It would have
saved a bunch of hackery like getRowClosestOrBefore.
> Get with closest_row_before on "hbase:meta" can return empty Cell during
> region merge/split
> -------------------------------------------------------------------------------------------
>
> Key: HBASE-18066
> URL: https://issues.apache.org/jira/browse/HBASE-18066
> Project: HBase
> Issue Type: Bug
> Components: hbase, regionserver
> Affects Versions: 1.3.1
> Environment: Linux (16.04.2), MacOS 10.11.6.
> Standalone and distributed HBase setup.
> Reporter: Andrey Elenskiy
> Attachments: TestGetWithClosestRowBeforeWhenSplit.java
>
>
> During region split/merge there's a brief period of time where doing a "Get"
> with "closest_row_before=true" on "hbase:meta" may return empty
> "GetResponse.result.cell" field even though parent, splitA and splitB regions
> are all in "hbase:meta". Both gohbase (https://github.com/tsuna/gohbase) and
> AsyncHBase (https://github.com/OpenTSDB/asynchbase) interprets this as
> "TableDoesNotExist", which is returned to the client.
> Here's a gist that reproduces this problem:
> https://gist.github.com/Timoha/c7a236b768be9220e85e53e1ca53bf96. Note that
> you have to use older HTable client (I used 1.2.4) as current versions ignore
> `Get.setClosestRowBefore(bool)` option.
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