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From Keith Turner <>
Subject Re: tservers running out of heap space
Date Thu, 29 Nov 2012 17:09:10 GMT
On Thu, Nov 29, 2012 at 11:14 AM, Anthony Fox <> 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

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