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From Denis Gabaydulin <gaba...@gmail.com>
Subject Re: [problem with OOM in nodes]
Date Fri, 21 Sep 2012 16:22:02 GMT
Found one more intersting fact.
As I can see in cfstats, compacted row maximum size: 386857368 !

On Fri, Sep 21, 2012 at 12:50 PM, Denis Gabaydulin <gabaden@gmail.com> wrote:
> Reports - is a SuperColumnFamily
>
> Each report has unique identifier (report_id). This is a key of
> SuperColumnFamily.
> And a report saved in separate row.
>
> A report is consisted of report rows (may vary between 1 and 500000,
> but most are small).
>
> Each report row is saved in separate super column. Hector based code:
>
> superCfMutator.addInsertion(
>   report_id,
>   "Reports",
>   HFactory.createSuperColumn(
>     report_row_id,
>     mapper.convertObject(object),
>     columnDefinition.getTopSerializer(),
>     columnDefinition.getSubSerializer(),
>     inferringSerializer
>   )
> );
>
> We have two frequent operation:
>
> 1. count report rows by report_id (calculate number of super columns
> in the row).
> 2. get report rows by report_id and range predicate (get super columns
> from the row with range predicate).
>
> I can't see here a big super columns :-(
>
> On Fri, Sep 21, 2012 at 3:10 AM, Tyler Hobbs <tyler@datastax.com> wrote:
>> I'm not 100% that I understand your data model and read patterns correctly,
>> but it sounds like you have large supercolumns and are requesting some of
>> the subcolumns from individual super columns.  If that's the case, the issue
>> is that Cassandra must deserialize the entire supercolumn in memory whenever
>> you read *any* of the subcolumns.  This is one of the reasons why composite
>> columns are recommended over supercolumns.
>>
>>
>> On Thu, Sep 20, 2012 at 6:45 AM, Denis Gabaydulin <gabaden@gmail.com> wrote:
>>>
>>> p.s. Cassandra 1.1.4
>>>
>>> On Thu, Sep 20, 2012 at 3:27 PM, Denis Gabaydulin <gabaden@gmail.com>
>>> wrote:
>>> > Hi, all!
>>> >
>>> > We have a cluster with virtual 7 nodes (disk storage is connected to
>>> > nodes with iSCSI). The storage schema is:
>>> >
>>> > Reports:{
>>> >     1:{
>>> >         1:{"value1":"some val", "value2":"some val"},
>>> >         2:{"value1":"some val", "value2":"some val"}
>>> >         ...
>>> >     },
>>> >     2:{
>>> >         1:{"value1":"some val", "value2":"some val"},
>>> >         2:{"value1":"some val", "value2":"some val"}
>>> >         ...
>>> >     }
>>> >     ...
>>> > }
>>> >
>>> > create keyspace osmp_reports
>>> >   with placement_strategy = 'SimpleStrategy'
>>> >   and strategy_options = {replication_factor : 4}
>>> >   and durable_writes = true;
>>> >
>>> > use osmp_reports;
>>> >
>>> > create column family QueryReportResult
>>> >   with column_type = 'Super'
>>> >   and comparator = 'BytesType'
>>> >   and subcomparator = 'BytesType'
>>> >   and default_validation_class = 'BytesType'
>>> >   and key_validation_class = 'BytesType'
>>> >   and read_repair_chance = 1.0
>>> >   and dclocal_read_repair_chance = 0.0
>>> >   and gc_grace = 432000
>>> >   and min_compaction_threshold = 4
>>> >   and max_compaction_threshold = 32
>>> >   and replicate_on_write = true
>>> >   and compaction_strategy =
>>> > 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy'
>>> >   and caching = 'KEYS_ONLY';
>>> >
>>> > =============================================
>>> >
>>> > Read/Write CL: 2
>>> >
>>> > Most of the reports are small, but some of them could have a half
>>> > mullion of rows (xml). Typical operations on this dataset is:
>>> >
>>> > count report rows by report_id (top level id of super column);
>>> > get columns (report_rows) by range predicate and limit for given
>>> > report_id.
>>> >
>>> > A data is written once and hasn't never been updated.
>>> >
>>> > So, time to time a couple of nodes crashes with OOM exception. Heap
>>> > dump says, that we have a lot of super columns in memory.
>>> > For example, I see one of the reports is in memory entirely. How it
>>> > could be possible? If we don't load the whole report, cassandra could
>>> > whether do this for some internal reasons?
>>> >
>>> > What should we do to avoid OOMs?
>>
>>
>>
>>
>> --
>> Tyler Hobbs
>> DataStax
>>

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