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https://issues.apache.org/jira/browse/CASSANDRA-7103?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Benedict resolved CASSANDRA-7103.
---------------------------------
Resolution: Fixed
Please consult the user list. You are updating the same row - certainly the
same storage row (anything sharing a partition key, in the case 'time_order' is
the same storage row)
It is helpful to understand the issues thoroughly before diving straight into
the bug tracker - this is what the user list and irc channels are for. The
developers and power users will be able to help you and indicate if a bug
really should be filed.
> Very poor performance with simple setup
> ---------------------------------------
>
> Key: CASSANDRA-7103
> URL: https://issues.apache.org/jira/browse/CASSANDRA-7103
> Project: Cassandra
> Issue Type: Bug
> Components: Core
> Environment: Fedora 19 (also happens on Ubuntu), Cassandra 2.0.7. dsc
> standard install
> Reporter: Martin Bligh
>
> Single node (this is just development, 32GB 20 core server), single disk
> array.
> Create the following table:
> {code}
> CREATE TABLE reut (
> time_order bigint,
> time_start bigint,
> ack_us map<int, int>,
> gc_strategy map<text, int>,
> gc_strategy_symbol map<text, int>,
> gc_symbol map<text, int>,
> ge_strategy map<text, int>,
> ge_strategy_symbol map<text, int>,
> ge_symbol map<text, int>,
> go_strategy map<text, int>,
> go_strategy_symbol map<text, int>,
> go_symbol map<text, int>,
> message_type map<text, int>,
> PRIMARY KEY (time_order, time_start)
> ) WITH
> bloom_filter_fp_chance=0.010000 AND
> caching='KEYS_ONLY' AND
> comment='' AND
> dclocal_read_repair_chance=0.000000 AND
> gc_grace_seconds=864000 AND
> index_interval=128 AND
> read_repair_chance=0.100000 AND
> replicate_on_write='true' AND
> populate_io_cache_on_flush='false' AND
> default_time_to_live=0 AND
> speculative_retry='99.0PERCENTILE' AND
> memtable_flush_period_in_ms=0 AND
> compaction={'class': 'SizeTieredCompactionStrategy'} AND
> compression={};
> {code}
> Now I just insert data into it (using python driver, async insert, prepared
> insert statement). Each row only fills out one of the gc_*, go_*, or ge_*
> columns, and there's something like 20-100 entries per map column,
> occasionally 1000, but it's nothing huge.
> First run 685 inserts in 1.004860 seconds (681.687053 Operations/s).
> OK, not great, but that's fine.
> Now throw 50,000 rows at it.
> Now run the first run again, and it takes 53s to do the same insert of 685
> rows - I'm getting about 10 rows per second.
> It's not IO bound - "iostat 1" shows quiescent for 9 seconds, then ~640KB
> write, then sleeps again - seems like the fflush sync.
> Run "nodetool flush" and performance goes back to as before!!!!
> Not sure why this gets so slow - I think it just builds huge commit logs and
> memtables, but never writes out to the data/ directory with sstables because
> I only have one table? That doesn't seem like a good situation.
> Worse ... if you let the python driver just throw stuff at it async (I think
> this allows up to 128 request if I understand the underlying protocol, then
> it gets so slow that a single write takes over 10s and times out). Seems to
> be some sort of synchronization problem in Java ... if I limit the concurrent
> async requests to the left column below, I get the number of seconds elapsed
> on the right:
> 1: 103 seconds
> 2: 63 seconds
> 8: 53 seconds
> 16: 53 seconds
> 32: 66 seconds
> 64: so slow it explodes in timeouts on write (over 10s each).
> I guess there's some thundering herd type locking issue in whatever Java
> primitive you are using to lock concurrent access to a single table. I know
> some of the Java concurrent.* stuff has this issue. So for the other tests
> above, I was limiting async writes to 16 pending.
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