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From "Philip Thompson (JIRA)" <>
Subject [jira] [Updated] (CASSANDRA-9323) Bulk loading is slow
Date Thu, 07 May 2015 15:09:02 GMT


Philip Thompson updated CASSANDRA-9323:
    Fix Version/s: 2.1.x

> Bulk loading is slow
> --------------------
>                 Key: CASSANDRA-9323
>                 URL:
>             Project: Cassandra
>          Issue Type: Bug
>            Reporter: Pierre N.
>             Fix For: 2.1.x
>         Attachments:
> When I bulk upload sstable created with CQLSSTableWriter, it's very slow. I tested on
a fresh cassandra node (nothing in keyspace, nor tables) with good hardware (8x2.8ghz, 32G
ram), but with classic hard disk (performance won't be improved with SSD in this case I think).

> When I upload from a different server an sstable using sstableloader I get an average
of 3 MB/sec, in the attached example I managed to get 5 MB/sec, which is still slow.
> During the streaming process  I noticed that one core of the server is full CPU, so I
think the operation is CPU bound server side. I quickly attached a sample profiler to the
cassandra instance and got the following output : 
> So, I think, but I may be wrong because it's inaccurate sampling, during streaming the
table is unserialized and reserialized to another sstable, and that's this unserialize/serialize
process which is taking a big amount of CPU, slowing down the insert speed.
> Can someone confirm the bulk load is slow ? I tested also on my computer and barely reach
> I don't understand the point of totally unserializing the table I just did build using
the CQLSStableWriter (because it's already a long process to build and sort the table), couldn't
it just copy the table from offset X to offset Y (using index information by example) without
unserializing/reserializing it ?

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