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From "stack (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-13374) Small scanners (with particular configurations) do not return all rows
Date Wed, 01 Apr 2015 22:39:54 GMT

    [ https://issues.apache.org/jira/browse/HBASE-13374?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14391642#comment-14391642
] 

stack commented on HBASE-13374:
-------------------------------

I don't follow this:

      localStartKey = createClosestRowBefore(lastResult.getRow());

If lastResult is from previous region and I am in new region, how can I get a row from before?

I don't remember why the skipRowOfFirstResult was added but I do remember it was hacky. If
you can get away without it, sweet.

Where was the int overflow? In the int i count?

How did you find the issues? Especially int overflow one?

> Small scanners (with particular configurations) do not return all rows
> ----------------------------------------------------------------------
>
>                 Key: HBASE-13374
>                 URL: https://issues.apache.org/jira/browse/HBASE-13374
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 1.0.0, 2.0.0, 1.1.0, 0.98.13
>            Reporter: Jonathan Lawlor
>            Assignee: Jonathan Lawlor
>            Priority: Blocker
>             Fix For: 2.0.0, 1.0.1, 1.1.0, 0.98.13
>
>         Attachments: HBASE-13374-v1.patch, small-scanner-data-loss-tests-0.98.patch,
small-scanner-data-loss-tests-branch-1.0+.patch
>
>
> I recently ran into a couple data loss issues with small scans. Similar to HBASE-13262,
these issues only appear when scans are configured in such a way that the max result size
limit is reached before the caching limit is reached. As far as I can tell, this issue affects
branches 0.98+
> I should note that after investigation it looks like the root cause of these issues is
not the same as HBASE-13262. Rather, these issue are caused by errors in the small scanner
logic (I will explain in more depth below). 
> Furthermore, I do know that the solution from HBASE-13262 has not made its way into small
scanners (it is being addressed in HBASE-13335). As a result I made sure to test these issues
with the patch from HBASE-13335 applied and I saw that they were still present.
> The following two issues have been observed (both lead to data loss):
> 1. When a small scan is configured with a caching value of Integer.MAX_VALUE, and a maxResultSize
limit that is reached before the region is exhausted, integer overflow will occur. This eventually
leads to a preemptive skip of the regions.
> 2. When a small scan is configured with a maxResultSize that is smaller than the size
of a single row, the small scanner will jump between regions preemptively. This issue seems
to be because small scanners assume that, unless a region is exhausted, at least 2 rows will
be returned from the server. This assumption isn't clearly state in the small scanners but
is implied through the use of {{skipRowOfFirstResult}}.
> Again, I would like to stress that the root cause of these issues is *NOT* related to
the cause of HBASE-13262. These issues occur because of inappropriate assumption made in the
small scanner logic. The inappropriate assumptions are:
> 1. Integer overflow will not occur when incrementing caching
> 2. At least 2 rows will be returned from the server unless the region has been exhausted
> I am attaching a patch that contains tests to display these issues. If these issues should
be split into separate JIRAs please let me know.



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