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HBase, mail # user - Custom preCompact RegionObserver crashes entire cluster on OOME: Heap Space


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Mesika, Asaf 2013-02-12, 05:46
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lars hofhansl 2013-02-12, 05:50
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Ted Yu 2013-02-12, 05:53
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Mesika, Asaf 2013-02-12, 07:22
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Anoop Sam John 2013-02-12, 06:44
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Mesika, Asaf 2013-02-12, 09:30
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Mesika, Asaf 2013-02-12, 09:13
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Anoop Sam John 2013-02-12, 09:22
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Mesika, Asaf 2013-02-12, 14:41
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Re: Custom preCompact RegionObserver crashes entire cluster on OOME: Heap Space
James Taylor 2013-02-12, 15:32
IMO, I don't think it's safe to change the KV in-place. We always create a new KV in our coprocessors.

James

On Feb 12, 2013, at 6:41 AM, "Mesika, Asaf" <[EMAIL PROTECTED]> wrote:

> I'm seeing a very strange behavior:
>
> If I run a scan during major compaction, I can see both the modified Delta Key Value (which contains the aggregated values - e.g. 9) and the other two delta columns that were used for this aggregated column (e.g, 3, 3) - as if Scan is exposed to the key values produced in mid scan.
> Could it be related to Cache somehow?
>
> I am modifying the KeyValue object received from the InternalScanner in preCompact (modifying its value).
>
> On Feb 12, 2013, at 11:22 AM, Anoop Sam John wrote:
>
>>> The question is: is it "legal" to change a KV I received from the InternalScanner before adding it the Result - i..e returning it from my own InternalScanner?
>>
>> You can change as per your need IMO
>>
>> -Anoop-
>>
>> ________________________________________
>> From: Mesika, Asaf [[EMAIL PROTECTED]]
>> Sent: Tuesday, February 12, 2013 2:43 PM
>> To: [EMAIL PROTECTED]
>> Subject: Re: Custom preCompact RegionObserver crashes entire cluster on OOME: Heap Space
>>
>> I am trying to reduce the amount of KeyValue generated during the preCompact, but I'm getting some weird behaviors.
>>
>> Let me describe what I am doing in short:
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>> We have a counters table, with the following structure:
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>> RowKey =  A combination of field values representing group by key.
>> CF = time span aggregate (Hour, Day, Month). Currently we have only for Hour.
>> CQ = Round-to-Hour timestamp (long).
>> Value = The count
>>
>> We collect raw data, and updates the counters table for the matched group by key, hour.
>> We tried using Increment, but discovered its very very slow.
>> Instead we've decided to update the counters upon compaction. We write the deltas into the same row-key, but a longer column qualifier: <RoundedToTheHourTS><Type><UniqueId>.
>> <Type> is: Delta or Aggregate.
>> Delta stands for a delta column qualifier we send from our client.
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>> in the preCompact, I create an InternalScanner which aggregates the delta column qualifier values and generates a new key value with Type Aggregate: <TS><A><UniqueID>
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>> The problem with this implementation that it consumes more memory.
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>> Now, I've tried avoiding the creation of the Aggregate type KV, by simply re-using the 1st delta column qualifier: simply changing its value in the KeyValue.
>> But from some reason, after a couple of minor / major compactions, I see data loss, when I count the values and compare them to the expected.
>>
>>
>> The question is: is it "legal" to change a KV I received from the InternalScanner before adding it the Result - i..e returning it from my own InternalScanner?
>>
>>
>>
>>
>>
>>
>> On Feb 12, 2013, at 8:44 AM, Anoop Sam John wrote:
>>
>>> Asaf,
>>>         You have created a wrapper around the original InternalScanner instance created by the compaction flow?
>>>
>>>> Where do the KV generated during the compaction process queue up before being written to the disk? Is this buffer configurable?
>>> When I wrote the Region Observer my assumption was the the compaction process works in Streaming fashion, thus even if I decide to generate a KV per KV I see, it still shouldn't be a problem memory wise.
>>>
>>> There is no queuing. Your assumption is correct only. It is written to the writer as and when. (Just like how memstore flush doing the HFile write) As Lars said a look at your code can tell if some thing is going wrong.  Do you have blooms being used?
>>>
>>> -Anoop-
>>> ________________________________________
>>> From: Mesika, Asaf [[EMAIL PROTECTED]]
>>> Sent: Tuesday, February 12, 2013 11:16 AM
>>> To: [EMAIL PROTECTED]
>>> Subject: Custom preCompact RegionObserver crashes entire cluster on OOME: Heap Space
>>>
>>> Hi,
>>>
>>> I wrote a RegionObserver which does preCompact.
>>> I activated in pre-production, and then entire cluster dropped dead: One RegionServer after another crashed on OutOfMemoryException: Heap Space.
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Ted Yu 2013-02-12, 16:00
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Anoop Sam John 2013-02-13, 05:29