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Accumulo >> mail # user >> tservers running out of heap space


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Re: tservers running out of heap space
On Thu, Nov 29, 2012 at 2:09 PM, Anthony Fox <[EMAIL PROTECTED]> wrote:

> We're not on 1.4 yet, unfortunately.  Are there any config params I can
> tweak to manipulate the compressor pool?
Not that I know of, but its been a while since I looked at that.
>
>
> On Thu, Nov 29, 2012 at 1:49 PM, Keith Turner <[EMAIL PROTECTED]> wrote:
>
>>
>>
>> On Thu, Nov 29, 2012 at 12:20 PM, Anthony Fox <[EMAIL PROTECTED]>wrote:
>>
>>> Compacting down to a single file is not feasible - there's about 70G in
>>> 255 tablets across 15 tablet servers.  Is there another way to tune the
>>> compressor pool or another mechanism to verify that this is the issue?
>>
>>
>> I suppose another way to test this would be to run a lot of concurrent
>> scans, but not enough to kill the tserver.  Then get a heap dump of the
>> tserver and see if it contains a lot of 128k or 256k (can not remember
>> exact size) byte arrays that are referenced by the compressor pool.
>>
>>
>>>
>>>
>>> On Thu, Nov 29, 2012 at 12:09 PM, Keith Turner <[EMAIL PROTECTED]> wrote:
>>>
>>>>
>>>>
>>>> On Thu, Nov 29, 2012 at 11:14 AM, Anthony Fox <[EMAIL PROTECTED]>wrote:
>>>>
>>>>> I am experiencing some issues running multiple parallel scans against
>>>>> Accumulo.  Running single scans works just fine but when I ramp up the
>>>>> number of simultaneous clients, my tablet servers die due to running out of
>>>>> heap space.  I've tried raising max heap to 4G which should be more than
>>>>> enough but I still see this error.  I've tried with
>>>>> table.cache.block.enable=false
>>>>> table.cache.index.enable=false, and table.scan.cache.enable=false and
>>>>> all combinations of caching enabled as well.
>>>>>
>>>>> My scans involve a custom intersecting iterator that maintains no more
>>>>> state than the top key and value.  The scans also do a bit of aggregation
>>>>> on column qualifiers but the result is small and the number of returned
>>>>> entries is only in the dozens.  The size of each returned value is only
>>>>> around 500 bytes.
>>>>>
>>>>> Any ideas why this may be happening or where to look for further info?
>>>>>
>>>>
>>>> One know issues is hadoops compressor pool.  If you have a tablet with
>>>> 8 files and you query 10 terms, you will allocate 80 decompressors.   Each
>>>> decompressor uses 128K.   If you have 10 concurrent queries, 10 terms, and
>>>> 10 files then you will allocate 1000 decompressors.    These decompressors
>>>> come from a pool that never shrinks.  So if you allocate 1000 at the same
>>>> time, they will stay around.
>>>>
>>>> Try compacting your table down to one file and rerun your query just to
>>>> see if that helps.   If it does, then thats an important clue.
>>>>
>>>>
>>>>
>>>>>
>>>>> Thanks,
>>>>> Anthony
>>>>>
>>>>
>>>>
>>>
>>
>