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From Emmanuel Lécharny <elecha...@gmail.com>
Subject Re: [Mavibot] Journal in BTree and RecordManager
Date Sun, 11 Aug 2013 07:37:27 GMT
Le 8/10/13 5:19 PM, Kiran Ayyagari a écrit :
> On Sat, Aug 10, 2013 at 8:30 PM, Stefan Seelmann <mail@stefan-seelmann.de>wrote:
>
>> Thanks for the response Kiran.
>>
>> In the meantime I think I found some problems in the BTree journal
>> manager thread and the BTreeFlushTest.
>>
>> 1. On Jenkins Windows Build the BTreeFlushTest failed [1]. The failing
>> assertion checks if the length of the journal file is greater than 0. As
>> the journal manager runs in its own thread it is not guaranteed that the
>> thread run and the journal may not be written. I was able to reproduce
>> it also on Linux when using the MultiThreadedMultiInvoker. I wonder why
>> the journal uses its own thread at all, I thought each modification
>> should immediately written and flushed to the journal?
>>
> yes, agree, not sure what was the reason behind it, Emmanuel may have a
> better answer to this

Well, I decided to accept the idea that we may not save all the
modifications in case of a crash, but as much as we can. The
modifications are pushed into a blocking queue, and the journal thread
process them as soon as they are some entries in this queue. Doing so
allow the main thread to write fast.

t may bnot be  the best solution.
>
>> 2. I think there is a bug in the BTree's journal manager code. The
>> flushModification() method returns a boolean. It is true when a Addition
>> or a Deletion was added, but then the journal manager thread stops. I
>> guess the boolean value should be inverted?
>>
>> yeap, it is a bug, the return values need to be inverted

+1
> Emmanuel,
>
>    I think the journal be deleted every time we flush(by calling flush())
> the data to disk?
>    cause at line 245 we have the below assertion, but journal has data
> cause we are not
>    truncating it (I ran the testFlushBTree() after inverting the above said
> return values)
>             // The journal must be empty
>             assertEquals( 0, journal.length() );

When we flush the btree, the journal should be emptied.


-- 
Regards,
Cordialement,
Emmanuel Lécharny
www.iktek.com 


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