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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. -- This message was sent by Atlassian JIRA (v6.3.4#6332)