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From "James Estes (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-14177) Full GC on client may lead to missing scan results
Date Fri, 31 Jul 2015 19:06:04 GMT
James Estes created HBASE-14177:

             Summary: Full GC on client may lead to missing scan results
                 Key: HBASE-14177
                 URL: https://issues.apache.org/jira/browse/HBASE-14177
             Project: HBase
          Issue Type: Bug
          Components: Client
    Affects Versions: 0.98.13, 0.98.12, 1.1.0
            Reporter: James Estes

After adding a large row, scanning back that row winds up being empty. After a few attempts
it will succeed (all attempts over the same data on an hbase getting no other writes).

Looking at logs, it seems this happens when there is memory pressure on the client and there
are several Full GCs that happen. Then messages that indicate that region locations are being
removed from the local client cache:

2015-07-31 12:50:24,647 [main] DEBUG org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation
 - Removed as a location of big_row_1438368609944,,1438368610048.880c849594807bdc7412f4f982337d6c.
for tableName=big_row_1438368609944 from cache

Blaming the GC may sound crazy, but if the test is run with -Xms4g -Xmx4g then it always passes
on the first scan attempt. Maybe the pause is enough to remove something from the cache, or
the client is using weak references somewhere?

More info http://mail-archives.apache.org/mod_mbox/hbase-user/201507.mbox/%3CCAE8tVdnFf%3Dob569%3DfJkpw1ndVWOVTkihYj9eo6qt0FrzihYHgw%40mail.gmail.com%3E

Test used to reproduce:

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