[ACCUMULO-3931] Repeated invocations of BatchScanner iterator().hasNext() causes MAC to become unresponsive

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Not A Problem
• Affects Version/s: 1.6.3, 1.7.0
• Component/s: mini
• Assignee: Eric C. Newton
• Reporter: Russ Weeks
• Created: 02/Jul/15 21:23
• Updated: 29/Jul/15 17:28
• Resolved: 07/Jul/15 16:23

Description

Steps to reproduce:

1. Instantiate a MiniAccumuloCluster with at least two tablet servers
2. Create a table; add splits to the table.
3. Add some mutations to the table distributed across the splits; flush the mutations.
4. Create a BatchScanner across the full range of the table.
5. Assert that the batch scanner has at least one KV pair by calling scanner.iterator().hasNext()
6. Repeat.

It doesn't seem to matter if you close the scanner and create a new one in between calls to hasNext, or if you re-seek the same scanner, or if the scanner is created in a static context and re-used by multiple tests or created by each test. Eventually you will see that the TabletServerBatchReaderIterator gets stuck polling its resultsQueue, preventing further tests from running.

This happens roughyl 20% of the time in 1.6 when I run mvn clean test -Dtest=org.apache.accumulo.minicluster.MultipleHasNextTest --projects minicluster, maybe less often in 1.7, and 100% of the time when I try to use the MAC in my company's product build environment, which uses gradle.

(I'll update with a link to a failing unit test as soon as I get an issue ID)

Sub-Tasks

• Improve documentation about multiple calls to iterator() sharing threads on single BatchScanner: Resolved