Jonathan Lawlor created HBASE-13374:
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Summary: 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
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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