[jira] [Created] (CASSANDRA-7103) Very poor performance with simple setup

["Martin Bligh (JIRA)" <ji...@apache.org>]

Martin Bligh created CASSANDRA-7103:
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             Summary: 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:

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={};

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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