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From "Enis Soztutar (JIRA)" <j...@apache.org>
Subject [jira] Updated: (NUTCH-893) DataStore.put() silently loses records when executed from multiple processes
Date Wed, 08 Sep 2010 13:23:32 GMT

     [ https://issues.apache.org/jira/browse/NUTCH-893?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Enis Soztutar updated NUTCH-893:
--------------------------------

    Attachment: NUTCH-893_v2.patch

Dogacan and I spent a fair amount of time to figure out the problem with this test. We have
checked and rechecked the code in gora-sql to make sure. However, the issue is that in TestGoraStorage#main(),
setup() is called, which issues a deleteByQuery() to delete all the data in the store. When
testMultiProcess() fires up lots of processes, some of the processes first start to write
data (only some of them are committed), but the newly started ones just delete those newly
written data. So this is a sync issue with the test itself. 

The uploaded new patch passes the test. So I am afraid, we need to update the test to cover
the issue in NUTCH-879. Andrzej, any suggestion for how to extend the test to reproduce NUTCH-879?

In the mean time, I will port this test to Gora as a part of http://github.com/enis/gora/issues#issue/50.
Thanks for the excellent patch. 
  



> DataStore.put() silently loses records when executed from multiple processes
> ----------------------------------------------------------------------------
>
>                 Key: NUTCH-893
>                 URL: https://issues.apache.org/jira/browse/NUTCH-893
>             Project: Nutch
>          Issue Type: Bug
>    Affects Versions: 2.0
>         Environment: Gora HEAD, SqlStore, MySQL 5.1, Ubuntu 10.4 x64, Sun JDK 1.6
>            Reporter: Andrzej Bialecki 
>            Priority: Blocker
>             Fix For: 2.0
>
>         Attachments: NUTCH-893.patch, NUTCH-893_v2.patch
>
>
> In order to debug the issue described in NUTCH-879 I created a test to simulate multiple
clients appending to webtable (please see the patch), which is the situation that we have
in distributed map-reduce jobs.
> There are two tests there: one that uses multiple threads within the same JVM, and another
that uses single thread in multiple JVMs. Each test first clears webtable (be careful!), and
then puts a bunch of pages, and finally counts that all are present and their values correspond
to keys. To make things more interesting each execution context (thread or process) closes
and reopens its instance of DataStore a few times.
> The multithreaded test passes just fine. However, the multi-process test fails with missing
keys, as many as 30%.

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