Pierre N. created CASSANDRA-9323:
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Summary: Bulk upload is slow
Key: CASSANDRA-9323
URL: https://issues.apache.org/jira/browse/CASSANDRA-9323
Project: Cassandra
Issue Type: Bug
Reporter: Pierre N.
Attachments: App.java
Hi,
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 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 :
https://i.imgur.com/IfLc2Ip.png
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 unserailize/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 1MB/sec
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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